[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [Qemu-devel] [PATCH 4/4] qemu-img: conditionally discard target on c
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-devel] [PATCH 4/4] qemu-img: conditionally discard target on convert |
Date: |
Thu, 18 Jul 2013 14:31:49 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130625 Thunderbird/17.0.7 |
Il 18/07/2013 13:04, Peter Lieven ha scritto:
>> But if you set BDRV_DISCARD_WRITE_ZEROES, then you always need a
>> fallback to bdrv_write_zeroes. Why not just call bdrv_write_zeroes to
>> begin with? That's why extending bdrv_write_zeroes is preferable.
> In this case wo do not need a flag to the function at all. If the
> driver sets bdi->write_zeroes_w_discard = 1 then bdrv_write_zeroes
> can use bdrv_discard to write zeroes and the driver has to
> ensure that all is zero afterwards.
Peter, you removed exactly the part of the email where I explained the
wrong part of your reasoning:
you cannot do that [discard in bdrv_write_zeroes] unconditionally.
Some operations can use it, some cannot. Think of SCSI disk
emulation: it must not discard is WRITE SAME is sent without the
UNMAP bit!
> If the driver would have a better method of writing zeroes than
> discard it simply should not set bdi->write_zeroes_w_discard = 1.
If the driver had a better method of writing zeroes than discard, it
simply should ignore the BDRV_MAY_UNMAP (or BDRV_MAY_DISCARD) flag in
its bdrv_write_zeros implementation.
With Kevin's proposal, there is no reason to add a flag to bdi. (Sorry
it took a few iterations to get it right).
Paolo
- Re: [Qemu-devel] [PATCH 4/4] qemu-img: conditionally discard target on convert, (continued)
- Re: [Qemu-devel] [PATCH 4/4] qemu-img: conditionally discard target on convert, Peter Lieven, 2013/07/17
- Re: [Qemu-devel] [PATCH 4/4] qemu-img: conditionally discard target on convert, Paolo Bonzini, 2013/07/17
- Re: [Qemu-devel] [PATCH 4/4] qemu-img: conditionally discard target on convert, Peter Lieven, 2013/07/17
- Re: [Qemu-devel] [PATCH 4/4] qemu-img: conditionally discard target on convert, Paolo Bonzini, 2013/07/17
- Re: [Qemu-devel] [PATCH 4/4] qemu-img: conditionally discard target on convert, Kevin Wolf, 2013/07/18
- Re: [Qemu-devel] [PATCH 4/4] qemu-img: conditionally discard target on convert, Paolo Bonzini, 2013/07/18
- Re: [Qemu-devel] [PATCH 4/4] qemu-img: conditionally discard target on convert, Kevin Wolf, 2013/07/18
- Re: [Qemu-devel] [PATCH 4/4] qemu-img: conditionally discard target on convert, Peter Lieven, 2013/07/18
- Re: [Qemu-devel] [PATCH 4/4] qemu-img: conditionally discard target on convert, Paolo Bonzini, 2013/07/18
- Re: [Qemu-devel] [PATCH 4/4] qemu-img: conditionally discard target on convert, Peter Lieven, 2013/07/18
- Re: [Qemu-devel] [PATCH 4/4] qemu-img: conditionally discard target on convert,
Paolo Bonzini <=
- Re: [Qemu-devel] [PATCH 4/4] qemu-img: conditionally discard target on convert, Peter Lieven, 2013/07/18
- Re: [Qemu-devel] [PATCH 4/4] qemu-img: conditionally discard target on convert, Paolo Bonzini, 2013/07/18
- Re: [Qemu-devel] [PATCH 4/4] qemu-img: conditionally discard target on convert, Peter Lieven, 2013/07/18
- Re: [Qemu-devel] [PATCH 4/4] qemu-img: conditionally discard target on convert, Paolo Bonzini, 2013/07/18
- Re: [Qemu-devel] [PATCH 4/4] qemu-img: conditionally discard target on convert, Peter Lieven, 2013/07/18
- Re: [Qemu-devel] [PATCH 4/4] qemu-img: conditionally discard target on convert, Paolo Bonzini, 2013/07/18
- Re: [Qemu-devel] [PATCH 4/4] qemu-img: conditionally discard target on convert, Peter Lieven, 2013/07/18
- Re: [Qemu-devel] [PATCH 4/4] qemu-img: conditionally discard target on convert, ronnie sahlberg, 2013/07/18
- Re: [Qemu-devel] [PATCH 4/4] qemu-img: conditionally discard target on convert, Peter Lieven, 2013/07/18
- Re: [Qemu-devel] [PATCH 4/4] qemu-img: conditionally discard target on convert, Paolo Bonzini, 2013/07/19