DISCLAIMER. English language used here only for compatibility (ASCII only), so any suggestions about my bad grammar (and not only it) will be greatly appreciated.

четверг, 16 декабря 2010 г.

[bash] Move array elements

Here is the task:
    1. move all array elements to offset (index) 'off'. I.e. such, that first
       array element will be at index 'off'.
    2. make holes (sequences of unset elements) in the array by moving
       different array parts to different offsets (indexes) off1, off2,
       off3,.. .

This can't be done by

    arr=( [i]="${arr[@]}" )

because "${[@]}" expansion works not as it should: it treats assignment prefix
specially, and in such case works the same as "${[*]}".

So, we should use some workaround, like

    #!/bin/bash

    declare -a arr=(
        1
        2
        3
        4
        5
    )
    declare -i off=15
    declare -p arr
    b=${arr[0]}
    unset arr[0]
    arr=( [off]=$b "${arr[@]}" )
    declare -p arr

This can be done simplier, but i'm not sure which version of bash this
requires

    #!/bin/bash

    declare -a arr=(
        1
        2
        3
        4
        5
    )
    declare -i off=15
    declare -p arr
    arr=( [off]=${arr[0]} "${arr[@]:1}" )
    declare -p arr

Second task can be solved like this

    #!/bin/bash

    declare -a arr=(
        1
        2
        3
        4
        5
        6
        7
        8
        9
        10
        11
        12
        13
    )
    declare -i off1=15 len1=2 i1=0
    declare -i off2=21 len2=3 i2=$((i1 + len1))
    declare -i off3=40 len3=4 i3=$((i2 + len2))
    declare -i off4=70        i4=$((i3 + len3))
    declare -p arr
    arr=( 
        [off1]=${arr[i1]}   "${arr[@]:i1 + 1: len1 - 1}"
        [off2]=${arr[i2]}   "${arr[@]:i2 + 1: len2 - 1}"
        [off3]=${arr[i3]}   "${arr[@]:i3 + 1: len3 - 1}"
        [off4]=${arr[i4]}   "${arr[@]:i4 + 1}"
    )
    declare -p arr

Note, that all existed holes in the array after such operations would be lost.

[bash] Write filenames to array.

Here is two general tasks:
    1. Assign strings (e.g. filenames) separated by '\0' from some input
       stream to corresponding array elements.
    2. Convert array into stream consisting from strings separated by '\0'.

I.e we have some bash script, which somewhere get such stream, e.g. by `find`
    
    find $root -wholename "*/$project" -prune -print0

and then we want to place this filenames into array elements. But there is a
problem: we can't use '\0' in IFS, so we can't split find's output stream
using bash word splitting expansion. And we can't use any other character to
separate filenames, because filename may contain any character.

One possible method (i don't know other, though it may be) is to transform
stream to bash code and then `eval` it.
   
But here is another problem: we can't simply escape string with double or
single quotes, because string may contain un-escaped double or single quotes
inside (find does not escape characters in filenames, and hence we assume,
that string contain un-escpaed characters, i.e written "as is"). For example

     a"'      b.txt

than after escaping with double quotes

    "a"'      b.txt"

or with single quotes

    'a"'      b.txt'

In both cases some part of string remain unescaped and not-matched quote
appears. (Write anothre example with command).


So, we can't escape string by commands like sed or awk, which perfom text
editing without string parsing. But we can use bash itself to parse and escape
string properly, and then output escaped result, like this

    eval "$(find $root -wholename "*/$project" -prune -print0 \
            | sort -z -s \
            | xargs -0 -x bash -c '
                            arr=( "$@" );
                            declare -p arr
                        ' escape_filename)"

(the last argument 'escape_filename' is used as $0. It may be any, but
required for correct work. For details see chapter 7.4.2 from 'info find')

Script for bash instance, invoked by xargs, may do some other operations with
strings, like

    j=15;
    eval "$(find $root -wholename "*/$project" -prune -print0 \
            | sort -z -s \
            | xargs -0 -x bash -c "
                            set -- \"\${@#$root/}\"
                            set -- \"\${@%$project}\"
                            arr2=( [$j]=\"\$1\" \"\${@:2}\" );
                            declare -p arr2
                        " escape_filename)"

Here we delete leading ($root) and trailing ($project) portions of filename
and then assign resulted set of strings to array starting at index $j.
Variables $root, $project and $j are substituted by main bash process before
executing pipeline.

If you use in this script array name you want assign to in main script, no
further editing of output will be needed.


Here is another example to what incorrect quoting may lead to. If we have in
input stream string like this

     a' rm -rf ~ '

then quote it with single quotes and add assignment (with sed, for example)

    var='a' rm -rf ~ ''

when it will be eval-ed it execute command

    rm -rf ~

Here is sample script

    #!/bin/bash

    str="a' ls ~ '"
    to_eval="$(echo "$str" | sed -e"s/^/var='/;s/$/'/")"
    eval "$to_eval"

четверг, 7 октября 2010 г.

[bash][part][draft]Return values from bash function

DISCLAIMER. English language used here only for compatibility (ASCII only), so any suggestions about my bad grammar (and not only it) will be greatly appreciated.

UPD. 2010.09.07
If we need to return several values from function, we can return through 
    - either setting some global variables,
    - or through pipe ("stdout").
    - or use both.
      
1. Global variables.

    If we do not want to hardcode these global variable names into script, we
    can pass their names as arguments and then use `eval` to assign values in
    child function,

        f() {
            ..
            eval "$1=\"a    b\""
        }
        f g1
        declare -p g1

    but in this case there is possible name conflicts between local function's
    variables and global ones. If local variable has the same name as global,
    it replaces it and we no longer able to set global variable in this
    child function.
    
2. Pipe.

    If we use pipe, we'll first gather all values from local child function's
    variables and send them into pipe, but then, in caller function, we'll
    parse pipe content to separate these values again and assign to proper
    variables. This is waste. Also, order, in which results will be outputed
    into pipe, should be fixed since cutting of result into separate values
    again and assigning them to proper variables into caller function assumes
    certain order.  And if this order sometimes accidently will change,
    returned values will be messed.

        f3() {
            local l1='a   b'
            local l2='   c d'
            echo "\"$l1\""
            echo "\"$l2\""
            return 0
        }
        eval "$(echo "$(f3)" | sed -e'1s/^/g1=/;2s/^/g2=/')"
        declare -p g1 g2

3. Mixed.

    But we can use both those techniques at the same time to eliminate all
    listed above problems each of them have.

    Names of global variables to be set should be passed through arguments,
    but in the pipe we'll send not raw values, but assignment statements with
    already expanded values, and in caller function we should simply execute
    them (assignment statements) in `eval`.  In such case we get:
        - no name conflicts, since we're no longer need global variables into
          child function: we need only their names to generate proper output,
          but values to them will be assigned into `eval` in caller function.
        - no parsing of pipe by caller, since child function knows names of
          variables to which caller want to assign values, and send the output
          with already prepared assignment statements (values in this
          assignment statements must be expanded in child function, since
          child's local variables will be deleted upon it returns).
        - Order of variables in child function's output may be any (except,
          very special cases, where one variable use the value of previous
          ones), since all assignments already written and no parsing
          required.

        f() {
            local l1='local   1'
            local l2='local 2'
            echo "g1=\"$l1\""
            echo "g2=\"$l2\""
            return 0
        }
        declare g1=''
        declare g2=''
        eval "$(f g1 g2)"
        declare -p g1 g2

Note1:
    - when function is called through command substitution, then it'll be
      executed in the subshell (unlike, when it's called normally, it is
      executed in the main shell), so you can _not_ set any parent shell's
      variable inside it. Thus, all parent shell's variable, which should be
      set must be written into pipe in assignment statements form.
    - you can not reinitialize array in parent shell using 'arr=( ${arr[@]} )'
      syntax, when writing to pipe, if array elements contain shell
      'metacharacters' (not IFS characters!). This is because in `eval`-ed
      script all values will be already expanded (yet before it'll be written
      into pipe) and will not contain any quotes, so they'll be broken into
      tokens (words and operators) by shell 'metacharacters' far before any
      expansions (including word splitting by 'IFS' characters) will take
      place.
    - the only way to reinitialize array in parent shell is to write either
      'arr[index]=value' for each element or `declare -p arr` into pipe.

Here is example.

# ./t.sh {{{

#!/bin/bash

f() {
    echo "SUBSH=$BASH_SUBSHELL" >/dev/tty
    arr1[3]='    g h  '
    arr2[3]='i    k  l'
    IFS=" "
    echo "arr1=( ${arr1[*]} )"
    echo "$(declare -p arr2)"
    return 0
}
declare -a arr1=(
    'a   b'
    'c      '
)
declare -a arr2=(
    '    d'
    '   e  f   '
)
eval "$(f)"
declare -p arr1 arr2

# }}}

Note2:

Even if we don't need any results from function, which write result into pipe,
following considerations should be looked at:
    - such function should always be invoked in subshell, even if we don't
      need its results. Otherwise, it'll be executed in the same shell as
      parent function and its actions with FDs may result in unexpected FD
      table state for parent.
    - FD=1 of such function should always be connected to something like
      '/dev/null'. Otherwise, it can write results somewhere you don't expect
      them for.

Example-1.

Here both functions f() and f2() return result through pipe, but function f()
does not need what f2() returns, so f2() is called (before f() moves pipe)
without subshell and without pipe connected. This results in the following
problems:
    - f2() closes 'fd_t_stdout' in the parent function's FD table, though f()
      thinks it's still open. This resluts in "9: Bad file descriptor error",
      when f() tries to move pipe and f() loses correct value for stdout.
      Hence, f() writes into pipe both output intended for 'stdout' and
      intended for 'pipe'.
    - f2() writes its output intended for 'pipe' into the _same_ pipe, as f()
      uses, because it was invoked before f() moves its own pipe.

# cat ./t.sh {{{
#!/bin/bash

declare -r -i fd_t_stdout=9
declare -r -i fd_t_pipe=7
declare -r log_file='./2.tmp'
declare -r read_file='/dev/zero'
[ -f "$log_file" ] && rm -f "$log_file"
exec 2>>"$log_file" <"$read_file"

f2() {
    echo "f2(): start: \$\$: $$, BASH=$BASHPID, SUBSH=$BASH_SUBSHELL" >>"$log_file"
    lsof -a -p $BASHPID -d'^mem,^txt,^rtd,^cwd' >>"$log_file"
    read -rsn1

    echo "f2(): move pipe" >>"$log_file"
    eval "exec $fd_t_pipe>&1 1>&$fd_t_stdout-"
    lsof -a -p $BASHPID -d'^mem,^txt,^rtd,^cwd' >>"$log_file"
    read -rsn1

    echo "f2(): write to stdout"

    echo "f2(): restore pipe" >>"$log_file"
    exec 1>&$fd_t_pipe-
    lsof -a -p $BASHPID -d'^mem,^txt,^rtd,^cwd' >>"$log_file"
    read -rsn1

    echo "f2(): write to pipe"
}
f() {
    echo "f(): start: \$\$: $$, BASH=$BASHPID, SUBSH=$BASH_SUBSHELL" >>"$log_file"
    lsof -a -p $BASHPID -d'^mem,^txt,^rtd,^cwd' >>"$log_file"
    read -rsn1

    f2
    echo "f(): move pipe" >>"$log_file"
    eval "exec $fd_t_pipe>&1 1>&$fd_t_stdout"
    lsof -a -p $BASHPID -d'^mem,^txt,^rtd,^cwd' >>"$log_file"
    read -rsn1

    echo "f(): write to stdout"

    echo "f(): restore pipe" >>"$log_file"
    eval "exec 1>&$fd_t_pipe-"
    lsof -a -p $BASHPID -d'^mem,^txt,^rtd,^cwd' >>"$log_file"
    read -rsn1

    echo "f(): write to pipe"
}
eval "exec $fd_t_stdout>&1"
v="$(f)"
echo "v: '$v'"
eval "exec $fd_t_stdout>&-"

# }}}
# ./t.sh >|./1.tmp {{{
f(): start: $$: 12681, BASH=12683, SUBSH=1
COMMAND   PID USER   FD   TYPE DEVICE SIZE    NODE NAME
t.sh    12683 root    0r   CHR    1,5          920 /dev/zero
t.sh    12683 root    1w  FIFO    0,6        31967 pipe
t.sh    12683 root    2w   REG    8,7   43 1590776 /home/sgf/new_tree/src/send_sms/2.tmp
t.sh    12683 root    9w   REG    8,7    0 1121662 /home/sgf/new_tree/src/send_sms/1.tmp
f2(): start: $$: 12681, BASH=12683, SUBSH=1
COMMAND   PID USER   FD   TYPE DEVICE SIZE    NODE NAME
t.sh    12683 root    0r   CHR    1,5          920 /dev/zero
t.sh    12683 root    1w  FIFO    0,6        31967 pipe
t.sh    12683 root    2w   REG    8,7  438 1590776 /home/sgf/new_tree/src/send_sms/2.tmp
t.sh    12683 root    9w   REG    8,7    0 1121662 /home/sgf/new_tree/src/send_sms/1.tmp
f2(): move pipe
COMMAND   PID USER   FD   TYPE DEVICE SIZE    NODE NAME
t.sh    12683 root    0r   CHR    1,5          920 /dev/zero
t.sh    12683 root    1w   REG    8,7    0 1121662 /home/sgf/new_tree/src/send_sms/1.tmp
t.sh    12683 root    2w   REG    8,7  805 1590776 /home/sgf/new_tree/src/send_sms/2.tmp
t.sh    12683 root    7w  FIFO    0,6        31967 pipe
f2(): restore pipe
COMMAND   PID USER   FD   TYPE DEVICE SIZE    NODE NAME
t.sh    12683 root    0r   CHR    1,5          920 /dev/zero
t.sh    12683 root    1w  FIFO    0,6        31967 pipe
t.sh    12683 root    2w   REG    8,7 1175 1590776 /home/sgf/new_tree/src/send_sms/2.tmp
f(): move pipe
./t.sh: line 36: 9: Bad file descriptor
COMMAND   PID USER   FD   TYPE DEVICE SIZE    NODE NAME
t.sh    12683 root    0r   CHR    1,5          920 /dev/zero
t.sh    12683 root    1w  FIFO    0,6        31967 pipe
t.sh    12683 root    2w   REG    8,7 1492 1590776 /home/sgf/new_tree/src/send_sms/2.tmp
f(): restore pipe
./t.sh: line 43: 7: Bad file descriptor
COMMAND   PID USER   FD   TYPE DEVICE SIZE    NODE NAME
t.sh    12683 root    0r   CHR    1,5          920 /dev/zero
t.sh    12683 root    1w  FIFO    0,6        31967 pipe
t.sh    12683 root    2w   REG    8,7 1812 1590776 /home/sgf/new_tree/src/send_sms/2.tmp

# }}}
# cat ./1.tmp {{{
f2(): write to stdout
v: 'f2(): write to pipe
f(): write to stdout
f(): write to pipe'

# }}}

Example-2.

If f() moves its pipe before calling f2(), but calls it also without subshell,
this will not be better:
    - f2() will write its output intended for 'pipe' into 'stdout', since
      stdout instead of pipe will be opened at FD=1, when f2() starts.
    - f2() replaces FD='fd_t_pipe' value into parent function's FD table, so
      saved f()'s pipe will be replaced with 'stdout' (since 'stdout' will be
      at FD=1 in f2()). So, f() loses correct value for its pipe and writes
      into 'stdout' both output intended for pipe and intended for 'stdout'.

# cat ./t.sh {{{
#!/bin/bash

declare -r -i fd_t_stdout=9
declare -r -i fd_t_pipe=7
declare -r log_file='./2.tmp'
declare -r read_file='/dev/zero'
[ -f "$log_file" ] && rm -f "$log_file"
exec 2>>"$log_file" <"$read_file"

f2() {
    echo "f2(): start: \$\$: $$, BASH=$BASHPID, SUBSH=$BASH_SUBSHELL" >>"$log_file"
    lsof -a -p $BASHPID -d'^mem,^txt,^rtd,^cwd' >>"$log_file"
    read -rsn1

    echo "f2(): move pipe" >>"$log_file"
    eval "exec $fd_t_pipe>&1 1>&$fd_t_stdout-"
    lsof -a -p $BASHPID -d'^mem,^txt,^rtd,^cwd' >>"$log_file"
    read -rsn1

    echo "f2(): write to stdout"

    echo "f2(): restore pipe" >>"$log_file"
    exec 1>&$fd_t_pipe-
    lsof -a -p $BASHPID -d'^mem,^txt,^rtd,^cwd' >>"$log_file"
    read -rsn1

    echo "f2(): write to pipe"
}
f() {
    echo "f(): start: \$\$: $$, BASH=$BASHPID, SUBSH=$BASH_SUBSHELL" >>"$log_file"
    lsof -a -p $BASHPID -d'^mem,^txt,^rtd,^cwd' >>"$log_file"
    read -rsn1

    echo "f(): move pipe" >>"$log_file"
    eval "exec $fd_t_pipe>&1 1>&$fd_t_stdout"
    lsof -a -p $BASHPID -d'^mem,^txt,^rtd,^cwd' >>"$log_file"
    read -rsn1

    f2
    echo "f(): write to stdout"

    echo "f(): restore pipe" >>"$log_file"
    eval "exec 1>&$fd_t_pipe-"
    lsof -a -p $BASHPID -d'^mem,^txt,^rtd,^cwd' >>"$log_file"
    read -rsn1

    echo "f(): write to pipe"
}
eval "exec $fd_t_stdout>&1"
v="$(f)"
echo "v: '$v'"
eval "exec $fd_t_stdout>&-"

# }}}
# ./t.sh >|./1.tmp {{{
f(): start: $$: 12713, BASH=12715, SUBSH=1
COMMAND   PID USER   FD   TYPE DEVICE SIZE    NODE NAME
t.sh    12715 root    0r   CHR    1,5          920 /dev/zero
t.sh    12715 root    1w  FIFO    0,6        32160 pipe
t.sh    12715 root    2w   REG    8,7   43 1590776 /home/sgf/new_tree/src/send_sms/2.tmp
t.sh    12715 root    9w   REG    8,7    0 1121662 /home/sgf/new_tree/src/send_sms/1.tmp
f(): move pipe
COMMAND   PID USER   FD   TYPE DEVICE SIZE    NODE NAME
t.sh    12715 root    0r   CHR    1,5          920 /dev/zero
t.sh    12715 root    1w   REG    8,7    0 1121662 /home/sgf/new_tree/src/send_sms/1.tmp
t.sh    12715 root    2w   REG    8,7  409 1590776 /home/sgf/new_tree/src/send_sms/2.tmp
t.sh    12715 root    7w  FIFO    0,6        32160 pipe
t.sh    12715 root    9w   REG    8,7    0 1121662 /home/sgf/new_tree/src/send_sms/1.tmp
f2(): start: $$: 12713, BASH=12715, SUBSH=1
COMMAND   PID USER   FD   TYPE DEVICE SIZE    NODE NAME
t.sh    12715 root    0r   CHR    1,5          920 /dev/zero
t.sh    12715 root    1w   REG    8,7    0 1121662 /home/sgf/new_tree/src/send_sms/1.tmp
t.sh    12715 root    2w   REG    8,7  893 1590776 /home/sgf/new_tree/src/send_sms/2.tmp
t.sh    12715 root    7w  FIFO    0,6        32160 pipe
t.sh    12715 root    9w   REG    8,7    0 1121662 /home/sgf/new_tree/src/send_sms/1.tmp
f2(): move pipe
COMMAND   PID USER   FD   TYPE DEVICE SIZE    NODE NAME
t.sh    12715 root    0r   CHR    1,5          920 /dev/zero
t.sh    12715 root    1w   REG    8,7    0 1121662 /home/sgf/new_tree/src/send_sms/1.tmp
t.sh    12715 root    2w   REG    8,7 1349 1590776 /home/sgf/new_tree/src/send_sms/2.tmp
t.sh    12715 root    7w   REG    8,7    0 1121662 /home/sgf/new_tree/src/send_sms/1.tmp
f2(): restore pipe
COMMAND   PID USER   FD   TYPE DEVICE SIZE    NODE NAME
t.sh    12715 root    0r   CHR    1,5          920 /dev/zero
t.sh    12715 root    1w   REG    8,7   22 1121662 /home/sgf/new_tree/src/send_sms/1.tmp
t.sh    12715 root    2w   REG    8,7 1752 1590776 /home/sgf/new_tree/src/send_sms/2.tmp
f(): restore pipe
./t.sh: line 43: 7: Bad file descriptor
COMMAND   PID USER   FD   TYPE DEVICE SIZE    NODE NAME
t.sh    12715 root    0r   CHR    1,5          920 /dev/zero
t.sh    12715 root    1w   REG    8,7   63 1121662 /home/sgf/new_tree/src/send_sms/1.tmp
t.sh    12715 root    2w   REG    8,7 2105 1590776 /home/sgf/new_tree/src/send_sms/2.tmp

# }}}
# cat ./1.tmp {{{
f2(): write to stdout
f2(): write to pipe
f(): write to stdout
f(): write to pipe
v: ''

# }}}

Example-3.

And here is how this can be done correctly. Shortly, we should call f2() like

    ( f2 >/dev/null )

In this case, f2() result will be discarded (but we do not need it, right?), but
f() will output its result as expected.

# cat ./t.sh {{{
#!/bin/bash

declare -r -i fd_t_stdout=9
declare -r -i fd_t_pipe=7
declare -r log_file='./2.tmp'
declare -r read_file='/dev/zero'
[ -f "$log_file" ] && rm -f "$log_file"
exec 2>>"$log_file" <"$read_file"

f2() {
    echo "f2(): start: \$\$: $$, BASH=$BASHPID, SUBSH=$BASH_SUBSHELL" >>"$log_file"
    lsof -a -p $BASHPID -d'^mem,^txt,^rtd,^cwd' >>"$log_file"
    read -rsn1

    echo "f2(): move pipe" >>"$log_file"
    eval "exec $fd_t_pipe>&1 1>&$fd_t_stdout-"
    lsof -a -p $BASHPID -d'^mem,^txt,^rtd,^cwd' >>"$log_file"
    read -rsn1

    echo "f2(): write to stdout"

    echo "f2(): restore pipe" >>"$log_file"
    exec 1>&$fd_t_pipe-
    lsof -a -p $BASHPID -d'^mem,^txt,^rtd,^cwd' >>"$log_file"
    read -rsn1

    echo "f2(): write to pipe"
}
f() {
    echo "f(): start: \$\$: $$, BASH=$BASHPID, SUBSH=$BASH_SUBSHELL" >>"$log_file"
    lsof -a -p $BASHPID -d'^mem,^txt,^rtd,^cwd' >>"$log_file"
    read -rsn1

    echo "f(): move pipe" >>"$log_file"
    eval "exec $fd_t_pipe>&1 1>&$fd_t_stdout"
    lsof -a -p $BASHPID -d'^mem,^txt,^rtd,^cwd' >>"$log_file"
    read -rsn1

    ( f2 >/dev/null )
    echo "f(): write to stdout"

    echo "f(): restore pipe" >>"$log_file"
    eval "exec 1>&$fd_t_pipe-"
    lsof -a -p $BASHPID -d'^mem,^txt,^rtd,^cwd' >>"$log_file"
    read -rsn1

    echo "f(): write to pipe"
}
eval "exec $fd_t_stdout>&1"
v="$(f)"
echo "v: '$v'"
eval "exec $fd_t_stdout>&-"

# }}}
# ./t.sh >|./1.tmp {{{
f(): start: $$: 12777, BASH=12779, SUBSH=1
COMMAND   PID USER   FD   TYPE DEVICE SIZE    NODE NAME
t.sh    12779 root    0r   CHR    1,5          920 /dev/zero
t.sh    12779 root    1w  FIFO    0,6        32627 pipe
t.sh    12779 root    2w   REG    8,7   43 1590776 /home/sgf/new_tree/src/send_sms/2.tmp
t.sh    12779 root    9w   REG    8,7    0 1121662 /home/sgf/new_tree/src/send_sms/1.tmp
f(): move pipe
COMMAND   PID USER   FD   TYPE DEVICE SIZE    NODE NAME
t.sh    12779 root    0r   CHR    1,5          920 /dev/zero
t.sh    12779 root    1w   REG    8,7    0 1121662 /home/sgf/new_tree/src/send_sms/1.tmp
t.sh    12779 root    2w   REG    8,7  409 1590776 /home/sgf/new_tree/src/send_sms/2.tmp
t.sh    12779 root    7w  FIFO    0,6        32627 pipe
t.sh    12779 root    9w   REG    8,7    0 1121662 /home/sgf/new_tree/src/send_sms/1.tmp
f2(): start: $$: 12777, BASH=12784, SUBSH=2
COMMAND   PID USER   FD   TYPE DEVICE SIZE    NODE NAME
t.sh    12784 root    0r   CHR    1,5          920 /dev/zero
t.sh    12784 root    1w   CHR    1,3          898 /dev/null
t.sh    12784 root    2w   REG    8,7  893 1590776 /home/sgf/new_tree/src/send_sms/2.tmp
t.sh    12784 root    7w  FIFO    0,6        32627 pipe
t.sh    12784 root    9w   REG    8,7    0 1121662 /home/sgf/new_tree/src/send_sms/1.tmp
t.sh    12784 root   10w   REG    8,7    0 1121662 /home/sgf/new_tree/src/send_sms/1.tmp
f2(): move pipe
COMMAND   PID USER   FD   TYPE DEVICE SIZE    NODE NAME
t.sh    12784 root    0r   CHR    1,5          920 /dev/zero
t.sh    12784 root    1w   REG    8,7    0 1121662 /home/sgf/new_tree/src/send_sms/1.tmp
t.sh    12784 root    2w   REG    8,7 1410 1590776 /home/sgf/new_tree/src/send_sms/2.tmp
t.sh    12784 root    7w   CHR    1,3          898 /dev/null
t.sh    12784 root   10w   REG    8,7    0 1121662 /home/sgf/new_tree/src/send_sms/1.tmp
f2(): restore pipe
COMMAND   PID USER   FD   TYPE DEVICE SIZE    NODE NAME
t.sh    12784 root    0r   CHR    1,5          920 /dev/zero
t.sh    12784 root    1w   CHR    1,3          898 /dev/null
t.sh    12784 root    2w   REG    8,7 1874 1590776 /home/sgf/new_tree/src/send_sms/2.tmp
t.sh    12784 root   10w   REG    8,7   22 1121662 /home/sgf/new_tree/src/send_sms/1.tmp
f(): restore pipe
COMMAND   PID USER   FD   TYPE DEVICE SIZE    NODE NAME
t.sh    12779 root    0r   CHR    1,5          920 /dev/zero
t.sh    12779 root    1w  FIFO    0,6        32627 pipe
t.sh    12779 root    2w   REG    8,7 2248 1590776 /home/sgf/new_tree/src/send_sms/2.tmp
t.sh    12779 root    9w   REG    8,7   43 1121662 /home/sgf/new_tree/src/send_sms/1.tmp

# }}}
# cat ./1.tmp {{{
f2(): write to stdout
f(): write to stdout
v: 'f(): write to pipe'

# }}}

четверг, 30 сентября 2010 г.

[draft][part] Shell I/O redirection

DISCLAIMER. English language used here only for compatibility (ASCII only), so any suggestions about my bad grammar (and not only it) will be greatly appreciated.

1. Open file descriptors table maps number (file descriptor - FD) into actual
   file to which output will be written.

    +----+------------+
    | FD | File       |
    +----+------------+
    | 0  |  /dev/vc/1 |
    +----+------------+
    | 1  |  /dev/vc/1 |
    +----+------------+
    | 2  |  /dev/vc/1 |
    +----+------------+
    | ...             |

2. Redirection operators (shell) affect (change) only 'File' column of the
   table. So, if program writes to FD=5 (write(5,..); call) you can _not_
   force it to write to another FD with shell redirection - you can only
   change the content of 'File' column in the FD=5 row (i.e to what file FD=5
   is mapped) and through that change to where output arrives at the end (to
   which file).

3. '/dev/stdout' and '/dev/stderr' are _not_ an actual files, they're _links_
   to what is _now_ opened at FD=1 and FD=2 correspondingly. I.e links to
   file specified in 'File' column of FD=1 and FD=2 rows.

# ls -l /dev/stdout /dev/stderr
lrwxrwxrwx 1 root root 15 Sep 30 07:56 /dev/stderr -> /proc/self/fd/2
lrwxrwxrwx 1 root root 15 Sep 30 07:56 /dev/stdout -> /proc/self/fd/1

4. In construction like 

        f() {
            echo "abc"
            return 0
        }
        res=$(f)

   function f() result are sent through pipe to the caller. I think, this is
   not clear to say, that result are sent through "stdout", though it's
   correct, since "stdout" is _not_ an actual file - it's a link to what is
   now opened at file descriptor 1, and now there will be pipe. By default,
   when function invoked through command substitution (function will be
   executed in a subshell), pipe is opened for writing at FD=1 for child
   process (function) and for reading at FD=3 for caller process.  So, if you
   use something like

        echo "abc"

   "abc" will be written into pipe (because `echo` always writes to FD=1). But
   if you want, that the way how we send result does not affect function's
   code, we should move 'pipe' from FD=1 into some unused FD and restore
   original FD=1 content. 

        exec 7>&1 1>&2
   
   When result will be ready, we move 'pipe' back to FD=1 and `echo` result
   into it.

        exec 1>&7-
        echo "result"

   Note, that for all child subshells pipe will be opened as well.


Example. Illustrates complete implementation, with several stacked functions
returning result through pipe.


#!/bin/bash

log='./t.log'
read_f='/dev/null'
rm -f $log

f2() {
    echo "f2(): SUBSH=$BASH_SUBSHELL" >>$log
    echo "f2(): BASHPID[$BASHPID]:" >>$log
    lsof -a -p $BASHPID -d '^mem,^cwd,^rtd,^txt' >>$log

    echo "f2(): stdout-1: ghi"
    echo "f2(): stderr-1: klm" >/dev/stderr

    echo "f2(): Before moving pipe somewhere" >>$log && read -n1 < $read_f
    eval "exec $save_pipe>&1 1>&$save_stdout-"
    echo "f2(): BASHPID[$BASHPID]:" >>$log
    lsof -a -p $BASHPID -d '^mem,^cwd,^rtd,^txt' >>$log

    echo "f2(): stdout-2: ghi"
    echo "f2(): stderr-2: klm" >/dev/stderr
    echo "f2(): Before exit f2()" >>$log && read -n1 < $read_f
    return 0
}
f() {
    echo "f(): SUBSH=$BASH_SUBSHELL" >>$log
    echo "f(): \$\$[$$]:" >>$log
    lsof -a -p $$ -d '^mem,^cwd,^rtd,^txt' >>$log
    echo "f(): BASHPID[$BASHPID]:" >>$log
    lsof -a -p $BASHPID -d '^mem,^cwd,^rtd,^txt' >>$log

    echo 'f(): stdout-1: abc'
    echo 'f(): stderr-1: def' >/dev/stderr

    echo "f(): Before moving pipe somewhere" >>$log && read -n1 < $read_f
    eval "exec $save_pipe>&1 1>&$save_stdout-"
    echo "f(): BASHPID[$BASHPID]:" >>$log
    lsof -a -p $BASHPID -d '^mem,^cwd,^rtd,^txt' >>$log

    echo 'f(): stdout-2: abc'
    echo 'f(): stderr-2: def' >/dev/stderr

    echo "f(): Before calling f2()" >>$log && read -n1 < $read_f
    eval "exec $save_stdout>&1"
    v=$(f2)
    echo "-$v-"
    eval "exec $save_stdout>&-"

    echo "f(): BASHPID[$BASHPID]:" >>$log
    lsof -a -p $BASHPID -d '^mem,^cwd,^rtd,^txt' >>$log

    echo "f(): Before restoring pipe" >>$log && read -n1 < $read_f
    exec >&$save_pipe-

    echo 'f(): stdout-3: abc'
    echo 'f(): stderr-3: def' >/dev/stderr

    echo "f(): BASHPID[$BASHPID]:" >>$log
    lsof -a -p $BASHPID -d '^mem,^cwd,^rtd,^txt' >>$log
    echo "f(): Before exit f()" >>$log && read -n1 < $read_f
    return 0
}
declare -r -i save_stdout=9
declare -r -i save_pipe=7
eval "exec $save_stdout>&1"
v=$(f)
eval "exec $save_stdout>&-"
echo "in main()"
echo "\$\$[$$]:" >>$log
lsof -a -p $$ -d '^mem,^cwd,^rtd,^txt' >>$log
echo "-$v-"



Here is illustration:

                             (subshell)
  main()                   ....................
 +--------------+          .   f()            .
 | 3r  pipe     | call f() . +--------------+ .
 | 9u  "stdout" |----------->| 1w  pipe(f)  | .
 +--------------+          . | 9u  "stdout" | .
                           . +--------------+ .
                           .     |            .
                           .     | move pipe(f)
                           .     |            .
                           .     v            .           (subshell)
                           . +--------------+ .         ....................
                           . | 1w  "stdout" | .         .   f2()           .
                           . | 7w  pipe(f)  | call f2() . +--------------+ .
                           . | 9-  (closed) |------------>| 1w  pipe(f2) | .
                           . +--------------+ .         . | 7w  pipe(f)  | .
                           .                  .         . | 9u  "stdout" | .
                           .                  .         . +--------------+ .
                           .                  .         .     |            .
                           .                  .         .     | move pipe(f2)
                           .                  .         .     | over pipe(f)
                           .                  .         .     |            .
                           .                  .         .     v            .
                           .                  .         . +--------------+ .
                           . +--------------+ . return  . | 1w  "stdout" | .
                           . | 1w  "stdout" |<------------| 7w  pipe(f2) | .
                           . | 7w  pipe(f)  | .         . | 9-  (closed) | .
                           . +--------------+ .         . +--------------+ .
                           .     |            .         ....................
                           .     | restore pipe(f)
                           .     |            .
                           .     v            .
                           . +--------------+ .
 +--------------+  return  . | 1w  pipe(f)  | .
 | 1u  "stdout" |------------| 7-  (closed) | .
 +--------------+          . +--------------+ .
                           ....................


And here is log (slightly edited)

# ./t.sh >|./1.tmp

f(): SUBSH=1
f(): $$[4794]:
COMMAND  PID USER   FD   TYPE DEVICE SIZE    NODE NAME
t.sh    4794 root    0u   CHR    4,1         5466 /dev/vc/1
t.sh    4794 root    1w   REG    8,7    0 1121662 .../1.tmp
t.sh    4794 root    2u   CHR    4,1         5466 /dev/vc/1
t.sh    4794 root    3r  FIFO    0,6        14132 pipe
t.sh    4794 root    9w   REG    8,7    0 1121662 .../1.tmp
t.sh    4794 root  255r   REG    8,7 2075 1121653 .../t.sh
f(): BASHPID[4796]:
COMMAND  PID USER   FD   TYPE DEVICE SIZE    NODE NAME
t.sh    4796 root    0u   CHR    4,1         5466 /dev/vc/1
t.sh    4796 root    1w  FIFO    0,6        14132 pipe
t.sh    4796 root    2u   CHR    4,1         5466 /dev/vc/1
t.sh    4796 root    9w   REG    8,7    0 1121662 .../1.tmp
f(): Before moving pipe somewhere
f(): BASHPID[4796]:
COMMAND  PID USER   FD   TYPE DEVICE SIZE    NODE NAME
t.sh    4796 root    0u   CHR    4,1         5466 /dev/vc/1
t.sh    4796 root    1w   REG    8,7    0 1121662 .../1.tmp
t.sh    4796 root    2u   CHR    4,1         5466 /dev/vc/1
t.sh    4796 root    7w  FIFO    0,6        14132 pipe
f(): Before calling f2()
f2(): SUBSH=2
f2(): BASHPID[4803]:
COMMAND  PID USER   FD   TYPE DEVICE SIZE    NODE NAME
t.sh    4803 root    0u   CHR    4,1         5466 /dev/vc/1
t.sh    4803 root    1w  FIFO    0,6        14194 pipe
t.sh    4803 root    2u   CHR    4,1         5466 /dev/vc/1
t.sh    4803 root    7w  FIFO    0,6        14132 pipe
t.sh    4803 root    9w   REG    8,7   19 1121662 .../1.tmp
f2(): Before moving pipe somewhere
f2(): BASHPID[4803]:
COMMAND  PID USER   FD   TYPE DEVICE SIZE    NODE NAME
t.sh    4803 root    0u   CHR    4,1         5466 /dev/vc/1
t.sh    4803 root    1w   REG    8,7   19 1121662 .../1.tmp
t.sh    4803 root    2u   CHR    4,1         5466 /dev/vc/1
t.sh    4803 root    7w  FIFO    0,6        14194 pipe
f2(): Before exit f2()
f(): BASHPID[4796]:
COMMAND  PID USER   FD   TYPE DEVICE SIZE    NODE NAME
t.sh    4796 root    0u   CHR    4,1         5466 /dev/vc/1
t.sh    4796 root    1w   REG    8,7   61 1121662 .../1.tmp
t.sh    4796 root    2u   CHR    4,1         5466 /dev/vc/1
t.sh    4796 root    7w  FIFO    0,6        14132 pipe
f(): Before restoring pipe
f(): BASHPID[4796]:
COMMAND  PID USER   FD   TYPE DEVICE SIZE  NODE NAME
t.sh    4796 root    0u   CHR    4,1       5466 /dev/vc/1
t.sh    4796 root    1w  FIFO    0,6      14132 pipe
t.sh    4796 root    2u   CHR    4,1       5466 /dev/vc/1
f(): Before exit f()
$$[4794]:
COMMAND  PID USER   FD   TYPE DEVICE SIZE    NODE NAME
t.sh    4794 root    0u   CHR    4,1         5466 /dev/vc/1
t.sh    4794 root    1w   REG    8,7   71 1121662 .../1.tmp
t.sh    4794 root    2u   CHR    4,1         5466 /dev/vc/1
t.sh    4794 root  255r   REG    8,7 2075 1121653 .../t.sh

четверг, 20 мая 2010 г.

[summary][draft][part] Tabs in vim

DISCLAIMER. English language used here only for compatibility (ASCII only), so any suggestions about my bad grammar (and not only it) will be greatly appreciated.

Status: summary.
State: draft,part.
Detailed description: Some tables for illustrate <Tab>'s handling in vim. See vim help for details.

Tabs in vim {{{

    'sts' and 'sta' options {{{

        Following options affect <Tab>s and indents:

            'tabstop'       'ts'
            'shiftwidth'    'sw'
            'softtabstop'   'sts'
            'smarttab'      'sta'
            'expandtab'     'et'

        'sw' and 'ts' define standard vim operations behavior, they are not
        switches for some features (hence they're always set and always used).
        But 'sts' and 'sta' enables additional features, which affect (change)
        some vim operations behavior (hence, they can be unset to turn feature
        off).

        Table below shows what option will be used to determine how many
        positions insert or delete during some editing operations depending on
        activated modes: both 'sts' and 'sta' are off (default), 'sts' set,
        'sta' set and both 'sts' and 'sta' set. When editing operation insert
        less (or more) positions, than real <Tab> counts for, mix from spaces
        and real <Tab>s are used.


    +--------------------------+-------------------------------------------+
    |    Operation             |   Will be inserted .. positions           |
    |                          +------+-----------+-----------+------------+
    |                          |      | +sts      | +sta      | +sts +sta  |
    +--------------------------+------+-----------+-----------+------------+
    | Use >> , etc             |  sw  | sw        |  sw       |  sw        |
    +--------------------------+------+-----------+-----------+------------+
    | Type <Tab> or <BS>       |  ts  | sts (mix) |           |            |
    |                          +      +           +-----------+------------+
    |     at the start of line |      |           |  sw (mix) |  sw (mix)  |
    |                          +      +           +-----------+------------+
    |     in other places      |      |           |  ts       |  sts (mix) |
    +--------------------------+------+-----------+-----------+------------+
    | Real <Tab> length        |  ts  | ts        |  ts       |  ts        |
    +--------------------------+------+-----------+-----------+------------+

    }}}
    ':retab' and changing 'ts' option value {{{

        'ts' option changes real tabstop, but does not change text. Hence,
        indents, which made according to old tabstop, probably will be messed
        (i.e there will be visible changes in text), but actual file remains
        untouched. So, using 'undo' after changing 'ts' has no sense.

        :retab command changes both 'ts' option and text according to new 'ts'
        value in such way, that all indents remain the same (there will be no
        visible changes), though actual file will be changed (to preserve
        visible indents :retab pads them, if necessary, with spaces). So,
        using 'undo' after :retab recover text to previous state, but not
        recover 'ts' to previous value, hence indents may be messed (like
        after you change only 'ts') and to recover visible text state you need
        set 'ts' to previous value. Table below summarizes that.


        +-------------------+---------------+-----------+
        |                   | Change 'ts'   | :retab    |
        +-------------------+---------------+-----------+
        | 'ts' changed?     | yes           | yes       |
        +-------------------+---------------+-----------+
        | File changed?     | no            | yes       |
        +-------------------+---------------+-----------+
        | Visible changes?  | yes           | no        |
        +-------------------+---------------+-----------+

    }}}

}}}


вторник, 4 мая 2010 г.

[method][draft][part][need_check] (bash) passing arguments to function

DISCLAIMER. English language used here only for compatibility (ASCII only), so any suggestions about my bad grammar (and not only it) will be greatly appreciated.

Status: method.
State: suggestion,draft,part,need_check.
Detailed description: One more method for passing arguments to bash function.

Outline: below under 'passing argument as pointer' i mean passing argument by name:
function f() {
}

declare var='abc'
f var  # not f "$var"
This may be considered as analogy for pointers (in C), i think :-)

1. Passing argument as pointer to function sometimes may require redefinition
   it as local variable in order to preserve referred data. Though, generally
   pointer used to provide to function ability to modify caller's environment,
   in bash it may be used, to skip unnecessary copying of big argument, if we
   want to redefine all positional parameters to local variables (names
   1, 2, 3,.. is bad whenever, and also positional parameters may be used for
   some tricks, so it's better, when they do not contain useful data).

        eval "
                $(declare -p $2 | sed -e's/^[^=]\+=/local -a shortopts=/' );
                $(declare -p $3 | sed -e's/^[^=]\+=/local -a longopts=/');
        "

   Above construction is, seemingly, the only way. To correctly redefine
   pointer to local variable we should honour several contraints:
        1. we should not define any local variable before all pointers will be
           expanded, because otherwise there is a chance, that defined local
           variable name is match with some pointed to variable's name and we
           lose access to it.
        2. we should preserve all special characters inside pointed data.

   To handle first constraint, we need `eval`.

   To handle second, we should properly quote expanded pointed to variable's
   value:

        ${[@]} - split elements correctly only during first expand, but in the
        second (done in `eval`) these boundaries will be lost and bash splits
        elements by 'metacharacters', not by IFS or anything else (info bash,
        ch-2).
        ${[*]} - my be used, perhaps, with IFS=',', and then.. something
        artificial to set up quoting by brace expansion. But this rarely works,
        though (i don't know working example).
        `declare` - seems, only way to obtain correct quoting without many
        evals and artificial tricks. But its output, perhaps, should be
        processed by some program to replace variable name to desired one.


[summary][draft][part] Bash script parsing

DISCLAIMER. English language used here only for compatibility (ASCII only), so any suggestions about my bad grammar (and not only it) will be greatly appreciated.

Status: summary.
State: draft,part.
Detailed description: illustration for info bash ch-2.

Bash script parsing units:

                    token = single unit
                   /     \
                 /         \
               /             \
             /                 \
          word                operator
         / | \                /     \
       /   |   \             /       \
     /     |     \          /         \
reserved  name    ..     control     redirection
word                     operator     operator


              metacharacter - separate words (or tokens?)
              /     \   
            /         \ 
          /             \
       blank           some (why not all?)
                       control operators

пятница, 23 апреля 2010 г.

[additions][done][unmaintained] Дополнение к инструкции по рациям Joker/Kenwood TK/JK-450S.

Status: additions.
State: done,unmaintained.
Detailed description: ...

TODO: [dropped] про набор номера канала.
TODO: [dropped] что включает функция F+0 ?


Таблица настроек субтонов CTCSS/DCS.

        +-----------------------+--------------------------------------+
        | Действие              |             Настройка                |
        |                       +------------------+-------------------+
        |                       | CTCSS            | DCS               |
        +-----------------------+------------------+-------------------+
        | Вкл/выкл CTCSS/DCS    |             (20) CT.DCS              |
        +-----------------------+--------+---------+---------+---------+
        | Уст. тон приема       | (7) RC | (21) CT | (9)  RD | (22) DC |
        +-----------------------+--------+         +---------+         |
        | Уст. тон передачи     | (8) TC |         | (10) TD |         |
        +-----------------------+--------+---------+---------+---------+

        Примечания.
                1. настройки (21) CT и (22) DC устанавливают и тон приема, и
                   тон передачи в одинаковые значения. Поэтому, если тон
                   приема и передачи будут одинаковые, то ими пользоваться
                   удобнее, чем двумя разными настройками (7)/(8) или
                   (9)/(10).

Настройка разных субтонов на прием/передачу и сдвиг частот приема/передачи.

        Сдвиг (как частот, так и субтонов) будет работать только при разговоре
        двух раций: третья (R-3) рация сможет либо общаться только с первой
        (R-1), либо только со второй (R-2). Для разговора c первой надо
        настроить третью, как вторую (см. схему ниже). В этом случае, третья
        не будет слышать вторую, а вторая не будет слышать третью.  Для
        разговора со второй надо настроить третью, как первую.

                    +-----------------------+ 
                    v                       | 
                    Rx                 +-------------------->  Rx 
              [Ch=B, DCS=Ab]           |    |            [Ch=A, DCS=Ad]
                +-----+                |    |                +-----+
                | R-1 |       Tx ------+    +------ Tx       | R-2 |
                |     | [Ch=A, DCS=Ad]        [Ch=B, DCS=Ab] |     |
                +-----+                                      +-----+

        Обозначения:
                Ch      - канал (частота);
                DCS     - тон DCS;

        Последовательность настройки:

                A=433.265, Ad=025I, B=433.255, Bd=023N

                1. Настраиваем рации на частоту приема.
                   R-1: ставим частоту 433.255;
                   R-2: ставим частоту 433.265;
                2. Установить сдвиг частот.
                   R-1: (6) OFFSET ставим на 0.010;
                   R-2: (6) OFFSET ставим на 0.010;
                3. Включить сдвиг частот.
                   R-1: (5) SFT ставим на '+';
                   R-2: (5) SFT ставим на '-';

                Сдвиг частот включен. Проверяем, что связь между рациями
                работает.

                4. Настраиваем DCS тон передачи.
                   R-1: (10) Td ставим на '025I';
                   R-2: (10) Td ставим на '023N';
                5. Настраиваем DCS тон приема.
                   R-1: (9) Rd ставим на '023N';
                   R-2: (9) Rd ставим на '025I';
                6. Включаем использование DCS тонов.
                   R-1: (20) CT.DCS ставим на 'DCS';
                   R-2: (20) CT.DCS ставим на 'DCS';

                DCS тона включены. Проверяем, что связь между рациями
                работает.

Режимы сканирование:
        (1) SCAN=  TO - остановка на найденном сигнале и продолжение 
                        через 5 секунд;
                   CO - остановка на найденном сигнале и продолжение через 5
                        секунд после пропадания сигнала;
                   SE - остановка на первом найденном сигнале;

Другие настройки:
        (2) TOT - Tx timeout Timer
                время (в секундах), после которого передача отключится даже
                при нажатой PTT (на случай залипшей PTT).
        (11) APO - Automatic Power-off
                автоматическое отключение рации через заданное время (в
                минутах).

В этой заметке использованы материалы с форумов 
tucson-club.ru (tucson-club.ru/forum/...)
и
lpd.radioscanner.ru (lpd.radioscanner.ru/topic...).

четверг, 4 февраля 2010 г.

LVM notes [draft]

DISCLAIMER. English language used here only for compatibility (ASCII only), so any suggestions about my bad grammar (and not only it) will be greatly appreciated.

Status: Many chapters missed and not posted here yet. Formatting may contain errors and missed entries.

UPD-01-03-10_14-32:
+ Title changed.
+ Metadata circular buffer description (draft) added.
+ LVM extent and stripe difference (in russian yet)
UPD:[2010.02.10]: небольшие улучшения в форматировании.

FIXME: длина строка >= 80.
FIXME: отступы.
FIXME: <> как обозначения, а не как html-тэги.
FIXME: расстояние между словами (см. вывод `od`).
FIXME: и шрифт дурацкий: нули почему-то меньше остальных букв :D

Text below may look much better in vim with folding enabled ('fdm=marker', 'fmr={{{,}}}'). Though indents are probably remain incorrect. Perhaps, someday i'll fix this :-)

Draft of metadata sectors layout:
  1. LVM label sector (0-r1) {{{

     Location: {{{
     - By default, `pvcreate` places the physical volume label
       in the sector 1 (2nd 512-byte block).
     - This label can optionally be placed in any of the first
       four sectors ('--labelsector' option). And due to LVM
       tools scan this first four sector for PV label, zeroing
       of them ('-Zy' option) is recommended.

     }}}
     Format: {{{
     Let consider on example:

> `pvcreate -vvv -Zy -M2 --metadatacopies=[012] --uuid=.. /dev/sdb4` {{{
> 
> /dev/sdb4: size is 58589055 sectors
> with mcopies=0: 58588927 available sectors
> with mcopies=1: 58588671 available sectors
>   metadata area at sector 8 size 376 sectors
> with mcopies=2: 58588416 available sectors
>   metadata area at sector 8 size 376 sectors
>   metadata area at sector 58588800 size 255 sectors
> 
> Area sizes (available sectors) in hex:
> data area size = 
>   (with mcopies=0) = 58588927 sectors = 0x37dfeff sectors = 0x06fbfdfe00 bytes
>   (with mcopies=1) = 58588671 sectors = 0x37dfdff sectors = 0x06fbfbfe00 bytes
>   (with mcopies=2) = 58588416 sectors = 0x37dfd00 sectors = 0x06fbfa0000 bytes
> meta area size =
>   (1st meta area) = 376 sectors = 192512 bytes = 0x02f000 bytes
>   (2nd meta area) = 255 sectors = 130560 bytes = 0x01fe00 bytes
> 
> Area offsets in hex:
> data area offset =
>   (with mcopies=0)   = 128 sectors = 65536 bytes = 0x010000 bytes
>   (with mcopies=1,2) = 384 sectors = 196608 bytes = 0x030000 bytes
> meta area offset =
>   (1st meta area) = 8 sectors = 4096 bytes = 0x1000 bytes
>   (2nd meta area) = 58588800 sectors = 0x37dfe80 sectors = 0x06fbfd0000 bytes
> 
> PV UUID = 'pesv0I-D0Ok-cVts-73Pg-vIaN-IRz2-LSldOn'
> 
> Sector 1 dump: {{{
> 
> Below for each 16 bytes row 1st line is for mcopies=0, 2nd - mcopies=1, 3rd -
> mcopies=2.
> 
> 000200 4c 41 42 45 4c 4f 4e 45 01 00 00 00 00 00 00 00
>          L   A   B   E   L   O   N   E soh nul nul nul nul nul nul nul
> 000200 4c 41 42 45 4c 4f 4e 45 01 00 00 00 00 00 00 00
>          L   A   B   E   L   O   N   E soh nul nul nul nul nul nul nul
> 000200 4c 41 42 45 4c 4f 4e 45 01 00 00 00 00 00 00 00
>          L   A   B   E   L   O   N   E soh nul nul nul nul nul nul nul
> --
> 000210 e3 bb 4a cb 20 00 00 00 4c 56 4d 32 20 30 30 31
>          c   ;   J   K  sp nul nul nul   L   V   M   2  sp   0   0   1
> 000210 3c a9 89 2c 20 00 00 00 4c 56 4d 32 20 30 30 31
>          <   )  ht   ,  sp nul nul nul   L   V   M   2  sp   0   0   1
> 000210 76 4b 22 d4 20 00 00 00 4c 56 4d 32 20 30 30 31
>          v   K   "   T  sp nul nul nul   L   V   M   2  sp   0   0   1
> --
> 000220 70 65 73 76 30 49 44 30 4f 6b 63 56 74 73 37 33
>          p   e   s   v   0   I   D   0   O   k   c   V   t   s   7   3
> 000220 70 65 73 76 30 49 44 30 4f 6b 63 56 74 73 37 33
>          p   e   s   v   0   I   D   0   O   k   c   V   t   s   7   3
> 000220 70 65 73 76 30 49 44 30 4f 6b 63 56 74 73 37 33
>          p   e   s   v   0   I   D   0   O   k   c   V   t   s   7   3
> --
> 000230 50 67 76 49 61 4e 49 52 7a 32 4c 53 6c 64 4f 6e
>          P   g   v   I   a   N   I   R   z   2   L   S   l   d   O   n
> 000230 50 67 76 49 61 4e 49 52 7a 32 4c 53 6c 64 4f 6e
>          P   g   v   I   a   N   I   R   z   2   L   S   l   d   O   n
> 000230 50 67 76 49 61 4e 49 52 7a 32 4c 53 6c 64 4f 6e
>          P   g   v   I   a   N   I   R   z   2   L   S   l   d   O   n
> --
> 000240 00 fe fd fb 06 00 00 00 00 00 01 00 00 00 00 00
>        nul   ~   }   { ack nul nul nul nul nul soh nul nul nul nul nul
> 000240 00 fe fb fb 06 00 00 00 00 00 03 00 00 00 00 00
>        nul   ~   {   { ack nul nul nul nul nul etx nul nul nul nul nul
> 000240 00 00 fa fb 06 00 00 00 00 00 03 00 00 00 00 00
>        nul nul   z   { ack nul nul nul nul nul etx nul nul nul nul nul
> --
> 000250 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>        nul nul nul nul nul nul nul nul nul nul nul nul nul nul nul nul
> 000250 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>        nul nul nul nul nul nul nul nul nul nul nul nul nul nul nul nul
> 000250 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>        nul nul nul nul nul nul nul nul nul nul nul nul nul nul nul nul
> --
> 000260 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>        nul nul nul nul nul nul nul nul nul nul nul nul nul nul nul nul
> 000260 00 00 00 00 00 00 00 00 00 10 00 00 00 00 00 00
>        nul nul nul nul nul nul nul nul nul dle nul nul nul nul nul nul
>        +0 +1 +2 +3 +4 +5 +6 +7 +8 +9 +a +b +c +d +e +f  
> 000260 00 00 00 00 00 00 00 00 00 10 00 00 00 00 00 00
>        nul nul nul nul nul nul nul nul nul dle nul nul nul nul nul nul
> --
> 000270 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>        nul nul nul nul nul nul nul nul nul nul nul nul nul nul nul nul
> 000270 00 f0 02 00 00 00 00 00 00 00 00 00 00 00 00 00
>        nul   p stx nul nul nul nul nul nul nul nul nul nul nul nul nul
> 000270 00 f0 02 00 00 00 00 00 00 00 fd fb 06 00 00 00
>        nul   p stx nul nul nul nul nul nul nul   }   { ack nul nul nul
> --
> 000280 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>        nul nul nul nul nul nul nul nul nul nul nul nul nul nul nul nul
> 000280 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>        nul nul nul nul nul nul nul nul nul nul nul nul nul nul nul nul
>        +0 +1 +2 +3 +4 +5 +6 +7 +8 +9 +a +b +c +d +e +f  
> 000280 00 fe 01 00 00 00 00 00 00 00 00 00 00 00 00 00
>        nul   ~ soh nul nul nul nul nul nul nul nul nul nul nul nul nul
> --
> 000290 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>        nul nul nul nul nul nul nul nul nul nul nul nul nul nul nul nul
> 000290 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>        nul nul nul nul nul nul nul nul nul nul nul nul nul nul nul nul
> 000290 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>        nul nul nul nul nul nul nul nul nul nul nul nul nul nul nul nul
> --
> (last NULL line repeated up to sector end)
> 
> }}}
> 
> }}}
     Notes: {{{
     - Size and offset below is in bytes.
     - All ranges below includes their boundaries.
     - Numbers (like size and offset) written on disk with least
       significant byte first. I.e least significant byte of
       number on disk will has less offset from disk beginning,
       than most significant.
     - All areas location rounded by sector boundary (512 bytes
       block), hence all size and offset values will be
       divisible by 512 (0x200), hence in hex them will always
       has NULL least significant byte (0x00).
     - I don't know for sure, is this NULL least significant
       byte actually written on disk or not, but rather is, than
       not. The most confusing place with this byte is beginning
       of data area size after UUID: NULL-byte at 0x240+0 may be
       NULL-termination byte after UUID as well as least
       significant byte of data area size value. I assume, that
       this is NULL least significant byte (see below).

     }}}
     Assumption: {{{
     - NULL least significant byte written on disk as is.
     - size value always occupy +0 -> +7 range of row.
     - offset value always occupy +8 -> +f range of row.
     - so, size and offset can be up to 16-digit hex number and
       occupy exactly one row.

     }}}
     Some sort of prove for assumptions: {{{
     - Throwing out part of number (NULL least significant byte)
       and not writing it to disk will not save space allocated
       for metadata, but may cause problems in future, when this
       least significant byte may become not NULL. So i don't
       see any sane reason for this.
     - Not writing NULL-termination byte after UUID looks
       possible, because UUID size is fixed (i think).
     - If offset and size regions on disk occupy different
       number of bytes, we either can not provide a method to
       address all allocated size (through offset) or will have
       offset values, which never be used - both is only
       introduces future incompatibilities. Hence, offset and
       size maximum allowed value should be the same and them
       should occupy the same number of bytes on disk.
     - Splitting one 16 bytes row on two equal parts by 8 bytes
       for size (fisrt) and offset (second) seems to be very
       reasonable: we have size and offset disk regions occupy
       the same number of bytes and also, as example shows,
       entire values (including NULL least significant byte)
       written into this regions.
     - Eventually, i do not find any conflict with any of my
       assumptions :-)

     }}}
     Short Physical Volume label sector format: {{{
     0x200  <LVM_magic_string>
     0x210  <smth_unknown_and_LVM_version>
     0x220  <PV_UUID>
     0x230  <PV_UUID(continue)>
     0x240  <data_size(8b)>      <data_offset(8b)>
     0x250  <NULL>
     0x260  <NULL(8b)>           <1st_meta_offset(8b)>
     0x270  <1st_meta_size(8b)>  <2nd_meta_offset(8b)>
     0x280  <2nd_meta_size(8b)>  <NULL(8b)>
     0x290  <NULL_(up_to_0x400)>

     }}}
     Detailed Physical Volume label sector format: {{{
     0x200+0 -> 0x200+f: LVM magic string. Identical for all
        three PVs.
     0x210+0 -> 0x210+7: Unknown.
     0x210+8 -> 0x210+b:  LVM version (i suppose).
     0x210+c -> 0x210+c:  Simply a separator (i suppose).
     0x210+d -> 0x210+f: LVM PV label sector (this sector)
        format version (i suppose).
     0x220+0 -> 0x230+f: PV UUID.
     0x240+0 -> 0x240+7: Data area size (number of available
        bytes).  Always present.
     0x240+8 -> 0x240+f: Data area offset. Always present.
     0x250+0 -> 0x250+f: NULL. Why?
     0x260+0 -> 0x260+7: NULL. Why?
     0x260+8 -> 0x260+f: 1st metadata circular buffer offset.
        Only for mcopies=1,2.
     0x270+0 -> 0x270+7: 1st metadata circular buffer size.
        Only for mcopies=1,2.
     0x270+8 -> 0x270+f: 2nd metadata circular buffer offset.
        Only for mcopies=2.
     0x280+0 -> 0x280+7: 2nd metadata circular buffer size
        Only for mcopies=2.
     0x280+8 -> 0x3f0+f: NULL and seems not used.

     }}}
     Last notes: {{{
     - metadata area size and location (sector number, where
       metadata circular buffer begins) can be obtained from
       `pvcreate -vvv` output. If no metadata areas (circular
       buffer) selected during PV creation (`pvcreate
       --metadatacopies=0`), than metadata buffer area size will
       be set to 120 sectors (it seems, that this is the lowest
       size), though will not be used (no pointers to metadata
       buffer will be in label sector and sector 8 remains
       unchanged as well). This can be determined by
       substraction count of available sectors from entire count
       of sectors on disk (you get 128 = 120 + 8).

     }}}

     }}}

  }}}
  2. LVM circular buffer (0-r1) {{{

     Short sector 8 format: {{{

     0x1000  <Unknown>
     0x1010  <Unknown(8b)>            <1st_meta_offset(8b)>
     0x1020  <1st_meta_size(8b)>      <latest_entry_offset(8b)>
     0x1030  <latest_entry_size(8b)>  <Unknown(8b)>
     0x1040  <NULLs_(up_to_0x1200)>

     }}}
     Detailed sector 8 format: {{{

     0x1000+0 -> 0x1000+f:  Unknown (2).
     0x1010+0 -> 0x1010+7:  Unknown (2).
     0x1010+8 -> 0x1010+f:  1st metadata circular buffer (this
          buffer) offset.
     0x1020+0 -> 0x1020+7:  1st metadata circular buffer (this
          buffer) size.
     0x1020+8 -> 0x1020+f:  Latest metadata entry in 1st circular
          buffer (this buffer) offset. Offset
       from beginning of the buffer, but
       NOT from beginning of the PV.
     0x1030+0 -> 0x1030+7:  Latest metadata entry in 1st
          circular buffer (this buffer) size,
       including null-terminator.
     0x1030+8 -> 0x1030+f:  Unknown (1).
     0x1040+0 -> 0x11f0+f:  NULLs and seems not used.

     (1): This number rather is not:
   - first unallocated PE (checked by value on example).
   - PE size (checked by value on example).
   - PV size (checked by value on example).
   - 2nd metadata buffer offset (it presents even in PVs
     with single metadata buffer).
   - latest metadata entry timestamp or smth else related
     to latest metadata entry (it differs for different
     PVs in the same VG, but latest metadata entry are
     the same for all PVs of the same VG).

   Also:
   - this value does not divisible without remainder by
     1024 or 512.
      (2): Notes:
       - range 0x1000+4 -> 0x1010+7 seems to be the same for
     all PVs (even from different VGs).

     }}}
     Metadata entries location: {{{
     - lvm metadata entry on disk location aligned roughly by
       sector boundary (512 bytes block). I.e words such 

   vg_mp3 {
   id = "YWvzHx-M1X5-TWtl-vCD1-w2zn-y0da-qui6PK"
   seqno = 50
   status = ["RESIZEABLE", "READ", "WRITE"]

       will be placed only at sector's boundary (beginning).
     - lvm metadata entry can occupy several sectors, though, if
       last occupied sector not fully filled, all trailing
       sector's part will not be cleared and, hence, it can
       contain some garbage (exactly, some part of data from
       previous record, occuping this sector).
       
     }}}
     Metadata entries format: {{{
     - Each metadata entry on disk ends with null-terminator.
     - On disk metadata timestamp (information about how and
       when metadata entry was created) written after VG
       description (information about volume group structure,
       see below) to which it relates (in contrast with metadata
       backup file, produced by `vgcfgbackup`, where timestamps
       written first).
     - On disk in metadata timestamp 'description' field is
       empty (but in metadata backup file, produced by
       `vgcfgbackup`, is not). (why?)

     }}}
     Last notes: {{{

     - When PV contain no metadata circular buffer areas
       ('--metadatacopies=0' by `pvcreate`), than restoring VG
       does not change anything in the PV metadata.
     - To obtain offset from beginning of PV to latest metadata
       entry in circular buffer, sum up '0x1010+8 -> 0x1010+f'
       value with '0x1020+8 -> 0x1020+f' value.
     - In order to locate latest metadata entry in raw 'on disk'
       metadata copy, you should look up metadata circular
       buffer (mostly, starting from sector 9, but if not, exact
       offsets you can obtained from PV label sector) dump
       splitted be sectors (512 bytes block) for sectors,
       beginning like

   vg_mp3 {
   id = "YWvzHx-M1X5-TWtl-vCD1-w2zn-y0da-qui6PK"
   seqno = 50
   status = ["RESIZEABLE", "READ", "WRITE"]

       This is the beginning of correct metadata entry.
       Afterwards, you should choose one with latest 'seqno'
       field.  As explained above, simply search by word 'seqno'
       may match with some garbage data after end of correct
       metadata entry. Though, because we look up for entry with
       latest 'seqno', anyway we'll select correct one. Also,
       note, that 'seqno' word may appear as garbage only in few
       first bytes of sector.

     }}}

  }}}


LVM extent and stripe:

(копия письма :-)
<...>
А под stripe-ами я имел в виду логический том LVM с stripe mapping, те,
например, вот такая команда

`lvcreate -vvv -i3 -I32 -l32000 -n striped_lv_3x32k test_vg`

И непонятно мне было почему LVM использует два вида блоков - extent и stripe,
и почему нельзя было реализовать все виды отображения (mapping) - и линейное,
и stripe mapping, - используя только один вид блоков. Но я тут еще посмотрел
логи `lvcreate -vvv` и в части, относящейся к активации логического раздела,
мне кажется, я нашел ответ. Хотя не уверен, что полностью правильный :-) Вот,
например:

--- Volume group ---
VG Name vg_4k
PE Size 4.00 KB
VG UUID M7TWGx-Rggp-Okru-nWGY-c7Mh-MaLi-LhYxFm

теперь если создать логический том (размером 32000 extent-ов) с stripe
mapping, разделенный на 3 физических тома и с размером stripe-а в 4КБайта
получится:

`lvcreate -vvv -i3 -I4 -l32000 -n s_lv_3x16k vg_4k`

<..>
Creating vg_4k-s_lv_3x16k
dm create vg_4k-s_lv_3x16k
LVM-M7TWGxRggpOkrunWGYc7MhMaLiLhYxFm0YvE0mFyjZS7Q103PbM4efKUb2lUXnR8
NF [16384]
Loading vg_4k-s_lv_3x16k table
Adding target: 0 256008 striped 3 8 7:1 384 7:2 384 7:0 384
dm table (253:0) OF [16384]
dm reload (253:0) NF [16384]
Resuming vg_4k-s_lv_3x16k (253:0)
dm resume (253:0) NF [16384]
<..>

Хотя это, конечно, и без лога известно было, но все же. Т.е вся
функциональность LVM реализована через device-mapper, но device-mapper ничего
не знает об extent-ах и не использует их. В своих таблицах он (`dmsetup
table`) для всех размеров и смещений использует дисковые блоки (512байт). А
для striped таблиц он также использует stripe - блок данных, который будет
записан на одно физическое устройство (т.е стандартное определение stripe-а).
Т.е получается, что device-mapper как раз и использует всего один тип блоков -
только stripe. И получается, что extent - блок, используемый только для
удобства управления LVM томами, а при работе LVM (I/O) он не используется. Т.е
блок, используемый только LVM тулсетом. Тогда становится понятно вот это
замечание из описания опции '-s' в `man vgcreate`:

-s, --physicalextentsize PhysicalExtentSize[kKmMgGtT]

<..>
If the volume group metadata uses lvm2 format those restrictions
do not apply, but having a large number of extents will slow
down the tools but have no impact on I/O performance to the log-
ical volume. The smallest PE is 1KB.

А ограничения на размеры stripe и extent, видимо, сделаны для того, чтобы все
они друг в друге помещались: 512байт - дисковый блок - степень двойки,
поэтому, наверно, stripe и extent тоже должны быть степенью двойки, чтобы
содержали целое число дисковых блоков. Кроме того, т.к и stripe, и extent
степень двойки, extent всегда будет содержать целое количество stripe-ов.
Правда, не очень понятно, почему device-mapper не позволяет устанавливать
размер stripe-а меньше 4Кбайт.
<...>