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Re: [Qemu-devel] [PATCH 1/7] block: only force IO completion in .bdrv_tr
From: |
Jeff Cody |
Subject: |
Re: [Qemu-devel] [PATCH 1/7] block: only force IO completion in .bdrv_truncate if we are shrinking |
Date: |
Wed, 6 Mar 2013 13:32:47 -0500 |
User-agent: |
Mutt/1.5.21 (2010-09-15) |
On Wed, Mar 06, 2013 at 06:50:56PM +0100, Peter Lieven wrote:
> 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.
>
That is a good point - what happens to QCOW now, if there is a block
job in progress (e.g. block-commit, block-stream, etc...)? I would
imagine -EBUSY gets thrown, since bdrv_truncate() checks
bdrv_in_use().
>
> >
> > 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, 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, 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
- Re: [Qemu-devel] [PATCH 1/7] block: only force IO completion in .bdrv_truncate if we are shrinking, Kevin Wolf, 2013/03/07