From: Christoph Hellwig <hch@lst.de>
To: Paul Brook <paul@codesourcery.com>
Cc: Kevin Wolf <kwolf@redhat.com>,
qemu-devel@nongnu.org, Christoph Hellwig <hch@lst.de>
Subject: Re: [Qemu-devel] [PATCH 1/5] block: add discard support
Date: Mon, 13 Dec 2010 16:43:57 +0100 [thread overview]
Message-ID: <20101213154357.GA5730@lst.de> (raw)
In-Reply-To: <201012111250.20905.paul@codesourcery.com>
On Sat, Dec 11, 2010 at 12:50:20PM +0000, Paul Brook wrote:
> > It's guest visible state, so it must not change due to migrations. For
> > the current implementation all values for it work anyway - if it's
> > smaller than the block size we'll zero out the remainder of the block.
>
> That sounds wrong. Surely we should leave partial blocks untouched.
While zeroing them is not required for qemu, the general semantics of
the XFS ioctl require it. It punches a hole, which means it's makes the
new area equivalent to a hole create by truncating a file to a larger
size and then only writing at the larger offset. The semantics for a
hole in all Unix filesystems is that we read back zeroes from them.
If we write into a sparse file at a not block aligned offset the
zeroing of the partial block also happens.
next prev parent reply other threads:[~2010-12-13 15:44 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-11-25 13:56 [Qemu-devel] [PATCH 0/5] add TRIM/UNMAP support Christoph Hellwig
2010-11-25 13:57 ` [Qemu-devel] [PATCH 1/5] block: add discard support Christoph Hellwig
2010-11-25 14:09 ` malc
2010-11-25 14:45 ` Stefan Hajnoczi
2010-11-25 13:57 ` [Qemu-devel] [PATCH 2/5] scsi-disk: support WRITE SAME (16) with unmap bit Christoph Hellwig
2010-11-25 14:10 ` malc
2010-11-25 13:57 ` [Qemu-devel] [PATCH 3/5] make dma_bdrv_io available to drivers Christoph Hellwig
2010-11-25 13:57 ` [Qemu-devel] [PATCH 4/5] ide: add TRIM support Christoph Hellwig
2010-11-25 14:10 ` malc
2010-11-25 13:57 ` [Qemu-devel] [PATCH 5/5] raw-posix: add discard support Christoph Hellwig
2010-12-01 15:35 ` [Qemu-devel] PATCH 0/5] add TRIM/UNMAP support, v2 Christoph Hellwig
2010-12-01 15:35 ` [Qemu-devel] [PATCH 1/5] block: add discard support Christoph Hellwig
2010-12-02 12:12 ` Kevin Wolf
2010-12-10 13:38 ` Christoph Hellwig
2010-12-11 12:50 ` Paul Brook
2010-12-13 15:43 ` Christoph Hellwig [this message]
2010-12-13 16:17 ` Paul Brook
2010-12-13 16:07 ` [Qemu-devel] " Paolo Bonzini
2010-12-13 16:15 ` Christoph Hellwig
2010-12-13 16:24 ` Paolo Bonzini
2010-12-01 15:35 ` [Qemu-devel] [PATCH 2/5] scsi-disk: support WRITE SAME (16) with unmap bit Christoph Hellwig
2010-12-01 15:35 ` [Qemu-devel] [PATCH 3/5] make dma_bdrv_io available to drivers Christoph Hellwig
2010-12-01 15:35 ` [Qemu-devel] [PATCH 4/5] ide: add TRIM support Christoph Hellwig
2010-12-02 14:07 ` Kevin Wolf
2010-12-10 13:39 ` Christoph Hellwig
2010-12-01 15:35 ` [Qemu-devel] [PATCH 5/5] raw-posix: add discard support Christoph Hellwig
2010-12-02 12:04 ` Kevin Wolf
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