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Re: [Qemu-devel] [PATCH 1/7] block: only force IO completion in .bdrv_tr
From: |
Peter Lieven |
Subject: |
Re: [Qemu-devel] [PATCH 1/7] block: only force IO completion in .bdrv_truncate if we are shrinking |
Date: |
Wed, 06 Mar 2013 18:50:56 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:15.0) Gecko/20120827 Thunderbird/15.0 |
Am 06.03.2013 15:47, schrieb Jeff Cody:
> Commit 9a665b2b made bdrv_truncate() call bdrv_drain_all(), but this breaks
> QCOW images, as well other future image formats (such as VHDX) that may call
> bdrv_truncate(bs->file) from within a read/write operation. For example, QCOW
> will cause an assert, due to tracked_requests not being empty (since the
> read/write that called bdrv_truncate() is still in progress).
>
> This modifies the check to only force the bdrv_drain_all() call if the BDS to
> be truncated is not growable, or if we are shrinking the BDS. Otherwise, if
> we
> are just growing the file, allow it to happen without forcing a call to
> bdrv_drain_all().
This will actually break iscsi_truncate(). Paolo requested that the
iscsi_tuncate command
should use sync I/O for rereading the LUN capacity. Using sync I/O is only
possible if
there are no async requests in-flight.
Looking at the source I have not found a place where bs->growable is set to 0
for any
block driver, maybe I miss something. Having bs->growable for iSCSI would also
be ok.
Shouldn't it be possible to call bdrv_drain_all() any time? There are other
places
where this is called. One I have in mind is e.g. if you cancel an ongoing block
migration.
Peter
>
> Signed-off-by: Jeff Cody <address@hidden>
> ---
> block.c | 10 ++++++++--
> 1 file changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/block.c b/block.c
> index 124a9eb..dce844c 100644
> --- a/block.c
> +++ b/block.c
> @@ -2450,8 +2450,14 @@ int bdrv_truncate(BlockDriverState *bs, int64_t offset)
> if (bdrv_in_use(bs))
> return -EBUSY;
>
> - /* There better not be any in-flight IOs when we truncate the device. */
> - bdrv_drain_all();
> + /* Don't force a drain if we are just growing the file - otherwise,
> + * using bdrv_truncate() from within a block driver in a read/write
> + * operation will cause an assert, because bdrv_drain_all() will assert
> if
> + * a tracked_request is still in progress. */
> + if (!bs->growable || offset < bdrv_getlength(bs)) {
> + /* There better not be any in-flight IOs when we truncate the
> device. */
> + bdrv_drain_all();
> + }
>
> ret = drv->bdrv_truncate(bs, offset);
> if (ret == 0) {
>
- [Qemu-devel] [PATCH 0/7] Initial VHDX support (and a bug fix for QCOW), Jeff Cody, 2013/03/06
- [Qemu-devel] [PATCH 1/7] block: only force IO completion in .bdrv_truncate if we are shrinking, Jeff Cody, 2013/03/06
- Re: [Qemu-devel] [PATCH 1/7] block: only force IO completion in .bdrv_truncate if we are shrinking,
Peter Lieven <=
- Re: [Qemu-devel] [PATCH 1/7] block: only force IO completion in .bdrv_truncate if we are shrinking, Paolo Bonzini, 2013/03/06
- Re: [Qemu-devel] [PATCH 1/7] block: only force IO completion in .bdrv_truncate if we are shrinking, Jeff Cody, 2013/03/06
- Re: [Qemu-devel] [PATCH 1/7] block: only force IO completion in .bdrv_truncate if we are shrinking, Paolo Bonzini, 2013/03/06
- Re: [Qemu-devel] [PATCH 1/7] block: only force IO completion in .bdrv_truncate if we are shrinking, Jeff Cody, 2013/03/06
- Re: [Qemu-devel] [PATCH 1/7] block: only force IO completion in .bdrv_truncate if we are shrinking, Peter Lieven, 2013/03/06
- Re: [Qemu-devel] [PATCH 1/7] block: only force IO completion in .bdrv_truncate if we are shrinking, Paolo Bonzini, 2013/03/06
- Re: [Qemu-devel] [PATCH 1/7] block: only force IO completion in .bdrv_truncate if we are shrinking, Kevin Wolf, 2013/03/07
- Re: [Qemu-devel] [PATCH 1/7] block: only force IO completion in .bdrv_truncate if we are shrinking, Peter Lieven, 2013/03/07