Re: [Qemu-devel] [PATCH 13/47] block: introduce block job error

[Paolo Bonzini]

Il 06/08/2012 11:29, Kevin Wolf ha scritto:
>>> >> Block jobs aren't really different from guests in that respect. Maybe
>>> >> the BB needs a second iostatus field that must explicitly be reset, and
>>> >> the old one keeps doing the stupid thing for compatibility's sake.
>> > 
>> > Or the iostatus for the target can just reside in the BlockJob... :)
> That wouldn't fix the problem in more than a single instance...

Even if you have problems in more than one device, you can still fix
them one at a time.

I think that we're fine with the current information.  In the long term
we will add the failing blockdev name to the blockjob iostatus.

>> > As much as I hate to invoke shortcuts, management may proceed without
>> > human help only in the ENOSPC case, and ENOSPC can only happens on the
>> > target.  Humans usually look at dmesg to find the source.
> dmesg doesn't contain information about corrupted qcow2 images, Sheepdog
> error codes from the server, etc.

True, guest dmesg doesn't help for block jobs.  (But network glitches
could be in dmesg or other sources of monitoring information).

But for block jobs your margins are small because you cannot take the VM
offline.  So if you get an EIO you can just do three things: first,
retry and see if it goes away (transient glitch); second, throw away the
target and see if it goes away; third, raise white flag and ask the VM
admin to cooperate, because the problem is likely in the source.

Paolo