[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [Qemu-devel] active block commit bug?
From: |
Jeff Cody |
Subject: |
Re: [Qemu-devel] active block commit bug? |
Date: |
Wed, 4 Jun 2014 20:12:14 -0400 |
User-agent: |
Mutt/1.5.21 (2010-09-15) |
On Wed, Jun 04, 2014 at 04:55:04PM -0600, Eric Blake wrote:
> Testing on Fedora 20 (JSON output slightly modified for legibility):
>
> $ qemu-kvm --version
> QEMU emulator version 2.0.0, Copyright (c) 2003-2008 Fabrice Bellard
> $ touch f
> $ qemu-kvm -qmp stdio -drive file=f
> <= {"QMP": {"version": {"qemu": {"micro": 0, "minor": 0, "major": 2},
> "package": ""}, "capabilities": []}}
>
> {"execute":"qmp_capabilities"}
> <= {"return": {}}
>
> {"execute":"blockdev-snapshot-sync","arguments":{"device":"ide0-hd0","snapshot-file":"g"}}
> Formatting 'g', fmt=qcow2 size=0 backing_file='f' backing_fmt='raw'
> encryption=off cluster_size=65536 lazy_refcounts=off
> <= {"return": {}}
>
> {"execute":"block-commit","arguments":{"device":"ide0-hd0","top":"g"}}
> {"timestamp": {"seconds": 1401921011, "microseconds": 498888}, "event":
> "BLOCK_JOB_COMPLETED", "data": {"device": "ide0-hd0", "len": 0,
> "offset": 0, "speed": 0, "type": "commit"}}
> <= {"return": {}}
>
> {"execute":"query-block-jobs"}
> <= {"return": []}
>
> Huh? I thought that an active commit was not supposed to complete
> automatically, but that the job would remain around until I either
> 'block-job-cancel' or 'block-job-complete' it. That is, I should have
> gotten a BLOCK_JOB_READY event and still see the job when I query for
> it. Where am I going wrong, or did I uncover a bug in active commit?
>
I tried repeating your findings, but I couldn't, until I noticed that
'f' was just a 0-length raw image in your test.
The snapshot file will be the same size, 0. So when we go to perform
the active commit, we short-circuit at the beginning, since we are
committing a zero-length image:
from block/mirror.c (active commit is a special mirror case):
static void coroutine_fn mirror_run(void *opaque)
{
MirrorBlockJob *s = opaque;
BlockDriverState *bs = s->common.bs;
int64_t sector_num, end, sectors_per_chunk, length;
uint64_t last_pause_ns;
BlockDriverInfo bdi;
char backing_filename[1024];
int ret = 0;
int n;
if (block_job_is_cancelled(&s->common)) {
goto immediate_exit;
}
s->common.len = bdrv_getlength(bs);
if (s->common.len <= 0) {
block_job_completed(&s->common, s->common.len);
return;
}
^^^^^
we exit early here, with a completed message, since there is
nothing to do.
If 'g' had increased to non-zero size, then you would have received a
BLOCK_JOB_READY instead.
-Jeff
- [Qemu-devel] active block commit bug?, Eric Blake, 2014/06/04
- Re: [Qemu-devel] active block commit bug?,
Jeff Cody <=
- Re: [Qemu-devel] active block commit bug?, Eric Blake, 2014/06/04
- Re: [Qemu-devel] active block commit bug?, Fam Zheng, 2014/06/04
- Re: [Qemu-devel] active block commit bug?, Eric Blake, 2014/06/04
- Re: [Qemu-devel] active block commit bug?, Fam Zheng, 2014/06/04
- Re: [Qemu-devel] active block commit bug?, Markus Armbruster, 2014/06/05
- Re: [Qemu-devel] active block commit bug?, Kevin Wolf, 2014/06/05
- Re: [Qemu-devel] active block commit bug?, Markus Armbruster, 2014/06/05
- Re: [Qemu-devel] active block commit bug?, Amos Kong, 2014/06/06