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Re: [Qemu-devel] [PATCH 4/4] qemu-img: conditionally discard target on c
From: |
Peter Lieven |
Subject: |
Re: [Qemu-devel] [PATCH 4/4] qemu-img: conditionally discard target on convert |
Date: |
Wed, 17 Jul 2013 16:21:24 +0200 |
Am 17.07.2013 um 12:45 schrieb Paolo Bonzini <address@hidden>:
> Il 17/07/2013 12:21, Peter Lieven ha scritto:
>>>> BTW, Peter and Ronnie: we were assuming that UNMAP with LBPRZ=1 always
>>>> zeroes blocks, but is that true for unaligned operations?
>> Good question, I will pass it to ronnie. My guess is that the command will
>> fail with
>> a check condition if it failed to unmap the data. From what Ronnie sent
>> earlier
>> it should be guaranteed that the blocks are at least zero after the unmap
>> command.
>
> I'm not so sure about that, SBC says explicitly that a misaligned unmap
> request "may result in unmap operations on fewer LBAs than requested".
>
> Perhaps it's better to do this:
>
> - if LBPWS=1, use WRITE SAME(16). For WRITE SAME it is explicit that
> "if the device server does not deallocate or anchor the LBA, then the
> device server shall perform the specified write operation". Expose the
> value of LBPRZ in the "discard zeroes" field of BlockDriverInfo.
>
> - if LBPWS=0, you can still support discard iff LBPU=1 and use UNMAP.
> But if LBPRZ=1 and LBPWS=0, you should not expose the "discard zeroes"
> field of BlockDriverInfo.
>
>> As for the qemu-img patch this shouldn't matter. It uses always blocks of
>> bdi->max_unmap
>> which should be a multiple of the alignment.
>
> Also, the remainder itself (which SBC calls "UNMAP GRANULARITY
> ALIGNMENT") may not be 0. I think the above trick (only exposing LBPRZ
> if you'll use WRITE SAME) will sidestep the problem. It may also remove
> the need to fall back to has_zero_init=1.
You mean has_zero_init = 0?
What is if the max write same size and max unmap differ?
Peter
>
> Paolo
- [Qemu-devel] [PATCH 2/4] iscsi: add .bdrv_get_info, (continued)
- [Qemu-devel] [PATCH 2/4] iscsi: add .bdrv_get_info, Peter Lieven, 2013/07/15
- [Qemu-devel] [PATCH 4/4] qemu-img: conditionally discard target on convert, Peter Lieven, 2013/07/15
- Re: [Qemu-devel] [PATCH 4/4] qemu-img: conditionally discard target on convert, Kevin Wolf, 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, Kevin Wolf, 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, 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 <=
- 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, 2013/07/17
- Re: [Qemu-devel] [PATCH 4/4] qemu-img: conditionally discard target on convert, ronnie sahlberg, 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, ronnie sahlberg, 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, 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