Re: [Qemu-devel] [PATCH] refresh filename after the node is replaced

[Max Reitz]

On 26.06.2015 16:27, Wen Congyang wrote:
> At 2015/6/26 21:47, Max Reitz Wrote:
> > On 25.06.2015 08:41, Wen Congyang wrote:
> > > We can use block job mirror to repair broken quorum files. But the
> > > command
> > > 'info block' doesn't output correct filename after block job mirror
> > > finishes.
> >
> > Which filename? The quorum filename is broken after this patch, too. In
>
> In my test, quorum has two children, s->common.bs->drv is quorum, and 
> s->to_replace
> is one of his child. Without this patch, info block will output 
> obsolete information.
> With this patch, the quorum's filename is right. I don't know why 
> quorum filename
> is broken.

Oh, yes, you are right, I forgot to execute block-job-complete. However, 
this patch relies on the Quorum BDS being the mirror source, which is 
the intentional use case but certainly not the only one:

$ x86_64-softmmu/qemu-system-x86_64 -drive 
if=none,id=quorum,driver=quorum,children.0.file.filename=test1.qcow2,children.1.file.filename=test2.qcow2,children.1.node-name=ch1,vote-threshold=1 
-drive if=none,id=drv,file=test2.qcow2 -qmp stdio
{"QMP": {"version": {"qemu": {"micro": 50, "minor": 3, "major": 2}, 
"package": ""}, "capabilities": []}}
{'execute':'qmp_capabilities'}
{"return": {}}
{'execute':'drive-mirror','arguments':{'device':'drv','target':'tmp.qcow2','format':'qcow2','node-name':'nch1','replaces':'ch1','sync':'full'}}
Formatting 'tmp.qcow2', fmt=qcow2 size=67108864 encryption=off 
cluster_size=65536 lazy_refcounts=off refcount_bits=16
{"return": {}}
{"timestamp": {"seconds": 1435331363, "microseconds": 217707}, "event": 
"BLOCK_JOB_READY", "data": {"device": "drv", "len": 0, "offset": 0, 
"speed": 0, "type": "mirror"}}
{'execute':'block-job-complete','arguments':{'device':'drv'}}
{"return": {}}
{"timestamp": {"seconds": 1435331373, "microseconds": 152945}, "event": 
"BLOCK_JOB_COMPLETED", "data": {"device": "drv", "len": 0, "offset": 0, 
"speed": 0, "type": "mirror"}}
{'execute':'query-block'}
{"return": [{"device": "quorum", "locked": false, "removable": true, 
"inserted": {"iops_rd": 0, "detect_zeroes": "off", "image": 
{"virtual-size": 67108864, "filename": "json:{\"children\": 
[{\"driver\": \"qcow2\", \"file\": {\"driver\": \"file\", \"filename\": 
\"test1.qcow2\"}}, {\"driver\": \"qcow2\", \"file\": {\"driver\": 
\"file\", \"filename\": \"test2.qcow2\"}}], \"driver\": \"quorum\", 
\"blkverify\": false, \"rewrite-corrupted\": false, \"vote-threshold\": 
1}", "format": "quorum"}, "iops_wr": 0, "ro": false, 
"backing_file_depth": 0, "drv": "quorum", "iops": 0, "bps_wr": 0, 
"write_threshold": 0, "encrypted": false, "bps": 0, "bps_rd": 0, 
"cache": {"no-flush": false, "direct": false, "writeback": true}, 
"file": "json:{\"children\": [{\"driver\": \"qcow2\", \"file\": 
{\"driver\": \"file\", \"filename\": \"test1.qcow2\"}}, {\"driver\": 
\"qcow2\", \"file\": {\"driver\": \"file\", \"filename\": 
\"test2.qcow2\"}}], \"driver\": \"quorum\", \"blkverify\": false, 
\"rewrite-corrupted\": false, \"vote-threshold\": 1}", 
"encryption_key_missing": false}, "tray_open": false, "type": 
"unknown"}, {"device": "drv", "locked": false, "removable": true, 
"inserted": {"iops_rd": 0, "detect_zeroes": "off", "image": 
{"virtual-size": 67108864, "filename": "test2.qcow2", "cluster-size": 
65536, "format": "qcow2", "actual-size": 200704, "format-specific": 
{"type": "qcow2", "data": {"compat": "1.1", "lazy-refcounts": false, 
"refcount-bits": 16, "corrupt": false}}, "dirty-flag": false}, 
"iops_wr": 0, "ro": false, "backing_file_depth": 0, "drv": "qcow2", 
"iops": 0, "bps_wr": 0, "write_threshold": 0, "encrypted": false, "bps": 
0, "bps_rd": 0, "cache": {"no-flush": false, "direct": false, 
"writeback": true}, "file": "test2.qcow2", "encryption_key_missing": 
false}, "tray_open": false, "type": "unknown"}, {"io-status": "ok", 
"device": "ide1-cd0", "locked": false, "removable": true, "tray_open": 
false, "type": "unknown"}, {"device": "floppy0", "locked": false, 
"removable": true, "tray_open": false, "type": "unknown"}, {"device": 
"sd0", "locked": false, "removable": true, "tray_open": false, "type": 
"unknown"}]}

This patch makes mirror_exit() refresh the name of the block job's 
device (in this case "drv"), which is not necessarily a parent of the 
node being replaced. Even if it were, imagine a configuration where 
there are two nested quorums, with the inner one being repaired using 
the "replaces" parameter for drive-mirror. In this case, this patch 
would fix the inner Quorum's file name, but not the outer one's.

I see two solutions to this issue: Either, we do it right and that 
means, if there is a change in the BDS graph (e.g. because of 
bdrv_swap()), we have to call bdrv_refresh_filename() on all of the 
changed BDS's parents. In order to be able to enumerate a BDS's parents, 
we need Kevin's series, as said before.

Or we revive my series "block: Drop BDS.filename" which drops the 
BDS.filename field completely and always rebuilds it if it is queried. 
This would fix the issue as well, however, there is a reason it has been 
lying around for nine months now, and that reason is that we did not yet 
fully examine the impacts of dropping that field, especially concerning 
libvirt.

Max

> Thanks
> Wen Congyang
>
> > order to fix this, we need to call bdrv_refresh_filename() after
> > bdrv_swap() on all BDSs which reference one of the swapped BDSs. I think
> > this will not be reasonably possible until Kevin's "bdrv_reopen()
> > overhaul" series is merged which introduces a generic parent-child
> > relationship for BDSs.
> >
> > Max
> >
> > > Signed-off-by: Wen Congyang <address@hidden>
> > > ---
> > >   block/mirror.c | 3 +++
> > >   1 file changed, 3 insertions(+)
> > >
> > > diff --git a/block/mirror.c b/block/mirror.c
> > > index 8aa2b21..2ca2c21 100644
> > > --- a/block/mirror.c
> > > +++ b/block/mirror.c
> > > @@ -351,6 +351,9 @@ static void mirror_exit(BlockJob *job, void 
> > > *opaque)
> > >               bdrv_set_backing_hd(s->base, NULL);
> > >               bdrv_unref(p);
> > >           }
> > > +        if (s->to_replace != s->common.bs) {
> > > +            bdrv_refresh_filename(s->common.bs);
> > > +        }
> > >       }
> > >       if (s->to_replace) {
> > >           bdrv_op_unblock_all(s->to_replace, s->replace_blocker);