Re: [Qemu-devel] [PATCH v2 1/1] quorum: Change vote rules for 64 bits hash

[Alberto Garcia]

On Tue 16 Feb 2016 03:15:44 AM CET, Changlong Xie <address@hidden> wrote:
> If quorum has two children(A, B). A do flush sucessfully, but B flush
> failed.  We MUST choice A as winner rather than just pick anyone of
> them. Otherwise the filesystem of guest will become read-only with
> following errors:
>
> end_request: I/O error, dev vda, sector 11159960
> Aborting journal on device vda3-8
> EXT4-fs error (device vda3): ext4_journal_start_sb:327: Detected abort journal
> EXT4-fs (vda3): Remounting filesystem read-only

Hi Xie,

Let's see if I'm getting this right:

- When Quorum flushes to disk, there's a vote among the return values of
  the flush operations of its members, and the one that wins is the one
  that Quorum returns.

- If there's a tie then Quorum choses the first result from the list of
  winners.

- With your patch you want to give priority to the vote with result == 0
  if there's any, so Quorum would return 0 (and succeed).

This seems to me like an ad-hoc fix for a particular use case. What if
you have 3 members and two of them fail with the same error code? Would
you still return 0 or the error code from the other two?

Also, is this only supposed to be used in FIFO mode? Your patch doesn't
seem to make any distinction.

Thanks!

Berto