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=head1 NAME |
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|
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Sys::FreezeThaw - stop and start all user processes on a machine |
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|
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=head1 SYNOPSIS |
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|
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use Sys::FreezeThaw; |
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|
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Sys::FreezeThaw::freezethaw { |
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# run code while system is frozen |
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}; |
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|
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my $token = Sys::FreezeThaw::freeze; |
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... do something ... |
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Sys::FreezeThaw::thaw $token; |
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|
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=head1 DESCRIPTION |
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|
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Operating Systems/Kernels current supported: Linux-2.6/3.0 with F</proc>. |
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|
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This module implements a very specific feature: stopping(freezing and |
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thawing/continuing all userspace processes on the machine. It works by |
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sending SIGSTOP to all processes, parent-process first, so that the wait |
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syscall will not trigger on stopped children. Restarting is done in |
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reverse order. |
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|
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Using the combined function Sys::FreezeThaw::freezethaw is recommended as |
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it will catch runtime errors, but stopping and restarting can be dine via |
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separate function calls. |
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|
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=head2 What could it possibly be sueful for?? |
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|
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Possible uses include: doing atomic file system operations (such as |
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replacing files while they are guaranteed not to be in use), or quieting |
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down a system to investigate suspicious behaviour. |
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|
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=over 4 |
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|
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=cut |
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|
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package Sys::FreezeThaw; |
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|
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use Carp; |
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|
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$VERSION = '0.02'; |
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|
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=item Sys::FreezeThaw::freezethaw { BLOCK } |
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|
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First tries to stop all processes. If successful, runs the given code block |
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(or code reference), then restarts all processes again. As the system is |
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basically frozen during the code block execution, it should be as fast as |
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possible. |
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|
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Runtime errors will be caught with C<eval>. If an exception occurs it will |
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be re-thrown after processes are restarted. If processes cannot be frozen |
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or restarted, this function will throw an exception. |
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|
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Signal handlers for SIGPIPE, SIGHUP, SIGALRM, SIGUSR1 and SIGUSR2 will |
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temporarily be installed, so if you want to catch these, you have to do so |
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yourself within the executed code block. |
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|
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Try to do as few things as possible. For example, outputting text might |
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cause a deadlock, as the terminal emulator on the other side of STDOUT |
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might be stopped, etc. |
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|
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The return value of the code block is ignored right now, and the function |
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doesn't yet return anything sensible. |
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|
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=item $token = Sys::FreezeThaw::freeze; |
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|
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Send SIGSTOP to all processes, and return a token that allows them to be |
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thawed again. |
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|
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If an error occurs, an exception will be thrown and all stopped processes |
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will automatically be thawed. |
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|
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=item Sys::FreezeThaw::thaw $token |
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|
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Take a token returned by Sys::FreezeThaw::freeze and send all processes |
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a CONT signal, in the order required for them not to receive child STOP |
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notifications. |
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|
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=cut |
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|
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# this is laughably broken, but... |
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sub yield { |
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select undef, undef, undef, 1/1000; |
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} |
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|
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# the maximum number of iterations per stop/cont etc. loop |
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# used to shield against catastrophic events (or bugs :) |
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# on current linux systems it can take an enourmous amount of |
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# time for some processes to stop, but usually it only takes |
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# one or two iterations. |
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sub MAX_WAIT() { 1000 } |
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|
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# return a list o fall pid's in the system, |
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# topologically sorted parent-first |
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# skips, keys %$exclude_pid, zombies and stopped processes |
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sub enum_pids($) { |
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my ($exclude_pid) = @_; |
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|
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opendir my $proc, "/proc" |
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or die "/proc: $!"; |
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my @pid = sort { $b <=> $a } |
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grep /^\d+/, |
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readdir $proc; |
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closedir $proc; |
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|
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my %ppid; |
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for (@pid) { |
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next if exists $exclude_pid->{$_}; |
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|
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open my $stat, "<", "/proc/$_/stat" |
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or next; |
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my ($state, $ppid, $vsize, $rss) = (split /\s+/, scalar <$stat>)[2,3,22,23]; |
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|
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next if $state =~ /^[TZX]/i; # stopped, zombies, dead |
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next unless $vsize || $rss; # skip kernel threads or other nasties |
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|
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$ppid{$_} = $ppid; |
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} |
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|
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# now topologically sort by parent-id |
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my @res; |
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while (scalar %ppid) { |
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my @pass; |
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|
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for my $pid (keys %ppid) { |
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if (!exists $ppid{$ppid{$pid}}) { |
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push @pass, $pid; |
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} |
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} |
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|
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delete $ppid{$_} for @pass; |
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|
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push @res, \@pass; |
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} |
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|
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\@res |
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} |
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|
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sub process_stopped($) { |
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open my $stat, "</proc/$_[0]/stat" |
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or return 1; |
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|
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return +(split /\s+/, <$stat>)[2] =~ /^[TZX]/i; |
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} |
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|
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sub thaw($) { |
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local $@; |
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|
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my $token = shift; |
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|
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for (reverse @$token) { |
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my @pids = @$_; |
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kill CONT => @pids; |
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|
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# now wait till processes actually run again before the next round |
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for (1..MAX_WAIT) { |
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@pids = grep process_stopped $_, @pids; |
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last unless @pids; |
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|
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yield; |
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} |
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} |
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} |
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|
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sub freeze() { |
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local $@; |
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|
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my @procs; |
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|
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eval { |
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for (1..MAX_WAIT) { |
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my $passes = enum_pids { 1 => 1, $$ => 1 }; |
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last unless @$passes; |
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|
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for (@$passes) { |
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my @pids = @$_; |
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push @procs, $_; |
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kill STOP => @pids; |
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|
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for (1..MAX_WAIT) { |
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@pids = grep !process_stopped $_, @pids; |
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last unless @pids; |
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|
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# wait till processes are really stopped |
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yield; |
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} |
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|
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die "unable to stop some processes: @pids" if @pids; |
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} |
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} |
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}; |
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|
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if ($@) { |
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thaw \@procs; |
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die $@; |
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} |
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|
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\@procs |
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} |
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|
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sub freezethaw(&) { |
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my ($code) = @_; |
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|
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my $token = freeze; |
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|
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eval { |
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local $SIG{HUP} = sub { die "ERROR: caught SIGHUP while system frozen" }; |
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local $SIG{PIPE} = sub { die "ERROR: caught SIGPIPE while system frozen" }; |
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local $SIG{ALRM} = sub { die "ERROR: caught SIGALRM while system frozen" }; |
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local $SIG{USR1} = sub { die "ERROR: caught SIGUSR1 while system frozen" }; |
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local $SIG{USR2} = sub { die "ERROR: caught SIGUSR2 while system frozen" }; |
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|
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$code->(); |
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}; |
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|
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thaw $token; |
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|
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die $@ if $@; |
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|
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() |
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} |
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|
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1; |
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|
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=back |
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|
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=head1 BUGS |
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|
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SIGCONT is not unnoticed by processes. Some programs (such as irssi-text) |
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respond by flickering (IMHO a bug in irssi-text). Other programs might |
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have other problems, but actual problems should be rare. However, one |
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shouldn't overuse this module. |
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|
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=head1 AUTHOR |
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|
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Marc Lehmann <schmorp@schmorp.de> |
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http://home.schmorp.de/ |
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|
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=cut |
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|
