[pve-devel] [PATCH installer v2 4/6] sys: command: allow terminating the process early from log subroutine

[Christoph Heiss <c.heiss@proxmox.com>]

If the logging subroutine $func returns CMD_FINISHED after processing a
line, the running subprocess is killed early.
This mechanism can be used when e.g. only a certain part of the output
of a (long-running) command is needed, avoiding the extra time it would
take the command to finish properly.

This is done in a entirely backwards-compatible way, i.e. existing
usages don't need any modification.

Signed-off-by: Christoph Heiss <c.heiss@proxmox.com>
---
Changes since v1:
  * introduced constant for return value (thanks Thomas!)
  * added documentation

 Proxmox/Sys/Command.pm | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/Proxmox/Sys/Command.pm b/Proxmox/Sys/Command.pm
index 6389b17..36e99c1 100644
--- a/Proxmox/Sys/Command.pm
+++ b/Proxmox/Sys/Command.pm
@@ -15,7 +15,9 @@ use Proxmox::Log;
 use Proxmox::UI;

 use base qw(Exporter);
-our @EXPORT_OK = qw(run_command syscmd);
+our @EXPORT_OK = qw(run_command syscmd CMD_FINISHED);
+
+use constant CMD_FINISHED => 1;

 my sub shellquote {
     my $str = shift;
@@ -79,7 +81,8 @@ sub syscmd {
 #
 # Arguments:
 # * $cmd - The command to run, either a single string or array with individual arguments
-# * $func - Logging subroutine to call, receives both stdout and stderr
+# * $func - Logging subroutine to call, receives both stdout and stderr. Might return CMD_FINISHED
+#           to exit early and ignore the rest of the process output.
 # * $input - Stdin contents for the spawned subprocess
 # * $noout - Whether to append any process output to the return value
 sub run_command {
@@ -163,7 +166,13 @@ sub run_command {
 		$logout .= $buf;
 		while ($logout =~ s/^([^\010\r\n]*)(\r|\n|(\010)+|\r\n)//s) {
 		    my $line = $1;
-		    $func->($line) if $func;
+		    if ($func) {
+			my $ret = $func->($line);
+			if (defined($ret) && $ret == CMD_FINISHED) {
+			    wait_for_process($pid, kill => 1);
+			    return $ostream;
+			}
+		    };
 		}

 	    } elsif ($h eq $error) {
--
2.43.0