Re: [pve-devel] [PATCH/RFC v2 qemu-server 3/3] restore_vma_archive: remove timeout for reading the device map

[Fabian Ebner <f.ebner@proxmox.com>]

Am 20.08.20 um 10:53 schrieb Thomas Lamprecht:
> On 12.08.20 12:01, Fabian Ebner wrote:
>> If there is no serious problem, it shouldn't be possible to run into
>> this timeout anyways. It's just (extracting and) reading the header of
>> the (compressed) vma file. And if there is a serious problem, then the
>> commands will most likely fail for a different reason, e.g. unable to open,
>> corrupt vma, etc.
>>
>> Signed-off-by: Fabian Ebner <f.ebner@proxmox.com>
>> ---
>>
>> New in v2
>>
>> Hope I'm not missing anything important.
> 
> the process doing the read can hang on IO for a long time, that can be pretty normal,
> especially on network attached storage and some IO load.
> Not saying that this isn't OK at all, but your commit message suggests misleadingly
> that this would either be very short or an immediate error, which isn't exactly true.
> 

True, so this timeout can trigger in such cases. The question is if we 
want to die after 5 seconds in that case (current behavior) or if we 
just give it as much time as it needs and let the user cancel if 
something hangs completely.

>>
>>   PVE/QemuServer.pm | 8 --------
>>   1 file changed, 8 deletions(-)
>>
>> diff --git a/PVE/QemuServer.pm b/PVE/QemuServer.pm
>> index 794819b..342114d 100644
>> --- a/PVE/QemuServer.pm
>> +++ b/PVE/QemuServer.pm
>> @@ -6162,8 +6162,6 @@ sub restore_vma_archive {
>>   
>>       $add_pipe->(['vma', 'extract', '-v', '-r', $mapfifo, $readfrom, $tmpdir]);
>>   
>> -    my $timeout = 5;
>> -
>>       my $devinfo = {};
>>   
>>       my $rpcenv = PVE::RPCEnvironment::get();
>> @@ -6260,9 +6258,6 @@ sub restore_vma_archive {
>>   	    local $SIG{QUIT} =
>>   	    local $SIG{HUP} =
>>   	    local $SIG{PIPE} = sub { die "interrupted by signal\n"; };
>> -	local $SIG{ALRM} = sub { die "got timeout reading device map\n"; };
>> -
>> -	alarm($timeout);
>>   
>>   	my $parser = sub {
>>   	    my $line = shift;
>> @@ -6273,7 +6268,6 @@ sub restore_vma_archive {
>>   		my ($dev_id, $size, $devname) = ($1, $2, $3);
>>   		$devinfo->{$devname} = { size => $size, dev_id => $dev_id };
>>   	    } elsif ($line =~ m/^CTIME: /) {
>> -		alarm(0);
>>   		&$print_devmap();
>>   		print $fifofh "done\n";
>>   		close($fifofh);
>> @@ -6285,8 +6279,6 @@ sub restore_vma_archive {
>>       };
>>       my $err = $@;
>>   
>> -    alarm(0);
>> -
>>       $restore_deactivate_volumes->($cfg, $devinfo);
>>   
>>       unlink $mapfifo;
>>
>