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Re: [Qemu-devel] [PATCH v2 06/16] block: do not parse BDRV_O_CACHE_WB in
From: |
Jeff Cody |
Subject: |
Re: [Qemu-devel] [PATCH v2 06/16] block: do not parse BDRV_O_CACHE_WB in raw block drivers |
Date: |
Thu, 13 Sep 2012 15:04:18 -0400 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:15.0) Gecko/20120828 Thunderbird/15.0 |
On 09/13/2012 02:56 PM, Paolo Bonzini wrote:
> 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.
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.
>
>> 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
>
- [Qemu-devel] [PATCH v2 02/16] block: make bdrv_set_enable_write_cache() modify open_flags, (continued)
- [Qemu-devel] [PATCH v2 02/16] block: make bdrv_set_enable_write_cache() modify open_flags, Jeff Cody, 2012/09/13
- [Qemu-devel] [PATCH v2 03/16] block: Framework for reopening files safely, Jeff Cody, 2012/09/13
- [Qemu-devel] [PATCH v2 04/16] block: move aio initialization into a helper function, Jeff Cody, 2012/09/13
- [Qemu-devel] [PATCH v2 06/16] block: do not parse BDRV_O_CACHE_WB in raw block drivers, Jeff Cody, 2012/09/13
- Re: [Qemu-devel] [PATCH v2 06/16] block: do not parse BDRV_O_CACHE_WB in raw block drivers, Paolo Bonzini, 2012/09/13
- Re: [Qemu-devel] [PATCH v2 06/16] block: do not parse BDRV_O_CACHE_WB in raw block drivers, Jeff Cody, 2012/09/13
- Re: [Qemu-devel] [PATCH v2 06/16] block: do not parse BDRV_O_CACHE_WB in raw block drivers, Paolo Bonzini, 2012/09/13
- Re: [Qemu-devel] [PATCH v2 06/16] block: do not parse BDRV_O_CACHE_WB in raw block drivers,
Jeff Cody <=
- Re: [Qemu-devel] [PATCH v2 06/16] block: do not parse BDRV_O_CACHE_WB in raw block drivers, Paolo Bonzini, 2012/09/13
- Re: [Qemu-devel] [PATCH v2 06/16] block: do not parse BDRV_O_CACHE_WB in raw block drivers, Paolo Bonzini, 2012/09/13
- Re: [Qemu-devel] [PATCH v2 06/16] block: do not parse BDRV_O_CACHE_WB in raw block drivers, Jeff Cody, 2012/09/13
- Re: [Qemu-devel] [PATCH v2 06/16] block: do not parse BDRV_O_CACHE_WB in raw block drivers, Paolo Bonzini, 2012/09/14
- Re: [Qemu-devel] [PATCH v2 06/16] block: do not parse BDRV_O_CACHE_WB in raw block drivers, Kevin Wolf, 2012/09/14
- Re: [Qemu-devel] [PATCH v2 06/16] block: do not parse BDRV_O_CACHE_WB in raw block drivers, Kevin Wolf, 2012/09/14
- Re: [Qemu-devel] [PATCH v2 06/16] block: do not parse BDRV_O_CACHE_WB in raw block drivers, Paolo Bonzini, 2012/09/14
- Re: [Qemu-devel] [PATCH v2 06/16] block: do not parse BDRV_O_CACHE_WB in raw block drivers, Kevin Wolf, 2012/09/14
- Re: [Qemu-devel] [PATCH v2 06/16] block: do not parse BDRV_O_CACHE_WB in raw block drivers, Paolo Bonzini, 2012/09/14
[Qemu-devel] [PATCH v2 10/16] block: qed image file reopen, Jeff Cody, 2012/09/13