Re: [Qemu-devel] [PATCH v2 06/16] block: do not parse BDRV_O_CACHE_WB in raw block drivers

[Paolo Bonzini]

Il 13/09/2012 19:17, Jeff Cody ha scritto:
>> > 
>> > Why does this matter?  If raw-posix was opened directly (i.e. without
>> > the bs->file indirection) this would cause a writethrough file to be
>> > incorrectly opened as writeback.
>> > 
>> > Paolo
>> > 
> The problem this patch was trying to work around is that
> bdrv_open_common() forces BDRV_O_CACHE_WB (commit e1e9b0ac), but that
> setting is not preserved in bs->open_flags, so it is lost on a reopen.

Perhaps we _should_ preserve that in bs->open_flags, while still using
the initial value of BDRV_O_CACHE_WB to initialize bs->enable_write_cache.

> Is there a scenario currently that has raw-posix opened directly as a
> writethrough file, or were you more concerned with future use?

Not for raw-posix, but IIRC some other protocol is opened directly
without a format on top.  rbd perhaps?  I'm concerned of having to work
around what seems like a bug elsewhere, in multiple protocols.

Paolo