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Re: [Qemu-devel] [PATCH/RFC] block: Ensure that block size constraints a
From: |
Kevin Wolf |
Subject: |
Re: [Qemu-devel] [PATCH/RFC] block: Ensure that block size constraints are considered |
Date: |
Wed, 21 Nov 2012 10:15:02 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:13.0) Gecko/20120605 Thunderbird/13.0 |
Am 21.11.2012 09:58, schrieb Christian Borntraeger:
> From: Heinz Graalfs <address@hidden>
>
> While testing IPL code (booting) for s390x we faced some problems
> with cache=none on dasds (4k block size) on bdrv_preads with length
> values != block size.
>
> This patch makes sure that bdrv_pread and friends work fine with
> unaligned access even with cache=none
> - propagate alignment value also into bs->file struct
> - modify the size in case of no cache to avoid EINVAL on
> pread() etc. (file was opened with O_DIRECT).
>
> This patch seems to cure the problems.
>
> CC: Kevin Wolf <address@hidden>
> CC: Stefan Hajnoczi <address@hidden>
> Signed-off-by: Heinz Graalfs <address@hidden>
> Signed-off-by: Christian Borntraeger <address@hidden>
> ---
> block.c | 3 +++
> block/raw-posix.c | 6 ++++++
> 2 files changed, 9 insertions(+)
>
> diff --git a/block.c b/block.c
> index 854ebd6..f23c562 100644
> --- a/block.c
> +++ b/block.c
> @@ -4242,6 +4242,9 @@ BlockDriverAIOCB *bdrv_aio_ioctl(BlockDriverState *bs,
> void bdrv_set_buffer_alignment(BlockDriverState *bs, int align)
> {
> bs->buffer_alignment = align;
> + if ((bs->open_flags & BDRV_O_NOCACHE)) {
> + bs->file->buffer_alignment = align;
> + }
Any reason to restrict this to BDRV_O_NOCACHE?
There have been patches to change the BDRV_O_NOCACHE flag from the
monitor, in which case bdrv_set_buffer_alignment() wouldn't be called
anew and O_DIRECT requests start to fail again.
> }
>
> void *qemu_blockalign(BlockDriverState *bs, size_t size)
> diff --git a/block/raw-posix.c b/block/raw-posix.c
> index f2f0404..baebf1d 100644
> --- a/block/raw-posix.c
> +++ b/block/raw-posix.c
> @@ -700,6 +700,12 @@ static BlockDriverAIOCB *paio_submit(BlockDriverState
> *bs, int fd,
> acb->aio_nbytes = nb_sectors * 512;
> acb->aio_offset = sector_num * 512;
>
> + /* O_DIRECT also requires an aligned length */
> + if (bs->open_flags & BDRV_O_NOCACHE) {
> + acb->aio_nbytes += acb->bs->buffer_alignment - 1;
> + acb->aio_nbytes &= ~(acb->bs->buffer_alignment - 1);
> + }
Modifying aio_nbytes, but not the iov looks wrong to me. This may work
in the handle_aiocb_rw_linear() code path, but not with actual vectored I/O.
Kevin