[libvirt] [PATCH] storage: Ignore block devices that fail format detection

[John Ferlan]

On 11/23/2015 09:13 AM, Ján Tomko wrote:
> On Fri, Oct 30, 2015 at 11:13:21AM -0400, John Ferlan wrote:
>> https://bugzilla.redhat.com/show_bug.cgi?id=1276198
>>
>> Prior to commit id '98322052' failure to saferead the block device would
>> cause an error to be logged and the device to be skipped while attempting
>> to discover/create a stable target path for a new LUN (NPIV).
>>
>> This was because virStorageBackendSCSIFindLUs ignored errors from
>> processLU and virStorageBackendSCSINewLun.
>>
>> Ignoring the failure allowed a multipath device with an "active" and
>> "ghost" to be present on the host with the "ghost" block device being
>> ignored. This patch will return a -2 to the caller indicating the desire
>> to ignore the block device since it cannot be used directly rather than
>> fail the pool startup.
>>
>> Additionally, it was found during some debugging that it was possible
>> for the virStorageBackendDetectBlockVolFormatFD to not detect a format,
>> which while not a probably - we probably should at least add some sort
>> of warning message.
>>
>> Signed-off-by: John Ferlan <jferlan at redhat.com>
>> ---
>>  src/storage/storage_backend.c      | 4 ++++
>>  src/storage/storage_backend_scsi.c | 7 ++++++-
>>  2 files changed, 10 insertions(+), 1 deletion(-)
>>
>> diff --git a/src/storage/storage_backend.c b/src/storage/storage_backend.c
>> index a375fe0..2de606f 100644
>> --- a/src/storage/storage_backend.c
>> +++ b/src/storage/storage_backend.c
>> @@ -1393,6 +1393,10 @@ virStorageBackendDetectBlockVolFormatFD(virStorageSourcePtr target,
>>          }
>>      }
>>  
>> +    if (target->format == VIR_STORAGE_POOL_DISK_UNKNOWN)
>> +        VIR_WARN("cannot determine the target format for '%s'",
>> +                 target->path);
>> +
>>      return 0;
>>  }
>>  
> 
> This change is unrelated to the other one. Also, is this warning really
> needed? I think leaving the format as 'unknown' is visible enough.
> 

No not needed - I can remove it or change to VIR_DEBUG - it was
certainly useful when debugging.

>> diff --git a/src/storage/storage_backend_scsi.c b/src/storage/storage_backend_scsi.c
>> index a593a2b..d60473d 100644
>> --- a/src/storage/storage_backend_scsi.c
>> +++ b/src/storage/storage_backend_scsi.c
>> @@ -224,9 +224,14 @@ virStorageBackendSCSINewLun(virStoragePoolObjPtr pool,
>>          goto cleanup;
>>      }
>>  
>> +    /* Failing to process the format is not fatal - we'll just skip
>> +     * this volume.
>> +     */
>>      if (virStorageBackendUpdateVolInfo(vol, true,
>> -                                       VIR_STORAGE_VOL_OPEN_DEFAULT) < 0)
>> +                                       VIR_STORAGE_VOL_OPEN_DEFAULT) < 0) {
>> +        retval = -2;
>>          goto cleanup;
> 
> Adding the VIR_STORAGE_VOL_OPEN_NOERROR flag and propagating it down to
> virStorageBackendDetectBlockVolFormatFD would be nicer.

So it's not an OPEN failure rather this a READ failure. The volume could
be opened and passing OPEN_NOERROR along in the "more general" is
probably not what should be done as that opens up a new classification
of errors that could get by.

I'll work on adding a similar read noerror setting

John

> 
> That way it can return -2 on EIO if the flag is present without spamming
> the logs. The other functions called by virStorageBackendUpdateVolInfo
> can also return -1 on a fatal error that way (although there do not seem
> to be any functions that could fail with NOERROR at the moment).
> 
> Jan
>