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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 15:52:50 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130625 Thunderbird/17.0.7 |
Il 18/07/2013 15:29, Peter Lieven ha scritto:
>>> 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.
>
> ok, but this would require an individual patch in every driver, wouldn't
> it. i am ok with that.
Yes (making the drivers return the flag in the BDI would also require
per-driver patches).
BDRV_MAY_UNMAP is an advisory flag, that the driver is free to ignore
(just like bdrv_discard can be ignored altogether).
block.c probably should avoid passing down BDRV_MAY_UNMAP altogether if
the BDRV_O_UNMAP flag is not set.
> the BDRV_MAY_DISCARD flag is at the end a hint if the driver can optimize
> writing zeroes by a discard or if real zeroes should be written e.g. to
> sanitize the device?
>
> talking for iscsi:
> bdrv->discard can remain to use UNMAP and silently fail if lbpu == 0.
> bdrv->write_zeroes will use writesame16 and set the unmap flag only if
> BDRV_MAY_DISCARD == 1 and BDRV_O_UNMAP == 1 and lbprz == 1.
> in case lbpws == 0 it will return -ENOSUP.
Almost: for LBPWS == 0 it can use WRITE SAME(16) without the unmap flag.
If that doesn't work either it can return -ENOTSUP.
Paolo
>
> Correct?
>
> Peter
>
- 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, 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, 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, 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
- Re: [Qemu-devel] [PATCH 4/4] qemu-img: conditionally discard target on convert, Peter Lieven, 2013/07/19
- Re: [Qemu-devel] [PATCH 4/4] qemu-img: conditionally discard target on convert, ronnie sahlberg, 2013/07/19