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 21:44, Paolo Bonzini ha scritto:
> Il 13/09/2012 21:04, Jeff Cody ha scritto:
>>>> 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.
>> That would work.  Part of the problem is that BDRV_O_CACHE_WB seems
>> overloaded; maybe bdrv_parse_cache_flags() should set a new flag, called
>> BDRV_O_CACHE_WCE, which can be used in lieu of enable_write_cache
>> (similar to getting rid of keep_read_only in favor of
>>  BDRV_O_ALLOW_RDWR).  And then bdrv_parse_cache_flags() would just not
>> set BDRV_O_CACHE_WB, which can then be used exclusively by the lower
>> layers for their parsing (and bdrv_open_common would just set
>> bs->open_flags to always have BDRV_O_CACHE_WB).
>>
>> Then patch 2/16 would change to having bdrv_set_enable_write_cache()
>> toggle BDRV_O_CACHE_WCE.
>>
> 
> Yeah, that would work.
> 
> Alternatively, we can keep this patch and leave bdrv_open_common as is;
> but then I would also prefer if raw-{posix,win32} took care of setting
> BDRV_O_CACHE_WB in bs->open_flags, so that the flags are consistent.
> This setting of BDRV_O_CACHE_WB can be extended later to other formats.

Hmm, no, what was I thinking...

But there is a very simple thing we can do:

- patch 2 can be left as is

- in patch 3 bdrv_reopen_queue, always add BDRV_O_CACHE_WB to
bs_entry->state.flags

- in patch 3 bdrv_reopen_commit, always leave BDRV_O_CACHE_WB aside:

    reopen_state->bs->open_flags         =
         (bs->open_flags & BDRV_O_CACHE_WB) |
         (reopen_state->flags & ~BDRV_O_CACHE_WB);

- this patch can be dropped completely.

Paolo