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Re: [Qemu-devel] [Qemu-block] [PATCH for-3.0] file-posix: Fix write_zero
From: |
Kevin Wolf |
Subject: |
Re: [Qemu-devel] [Qemu-block] [PATCH for-3.0] file-posix: Fix write_zeroes with unmap on block devices |
Date: |
Thu, 26 Jul 2018 18:41:43 +0200 |
User-agent: |
Mutt/1.9.1 (2017-09-22) |
Am 26.07.2018 um 18:22 hat Nir Soffer geschrieben:
> On Thu, Jul 26, 2018 at 2:33 PM Kevin Wolf <address@hidden> wrote:
>
> > The BLKDISCARD ioctl doesn't guarantee that the discarded blocks read as
> > all-zero afterwards, so don't try to abuse it for zero writing. We try
> > to only use this if BLKDISCARDZEROES tells us that it is safe, but this
> > is unreliable on older kernels and a constant 0 in newer kernels. In
> > other words, this code path is never actually used with newer kernels,
> > so we don't even try to unmap while writing zeros.
> >
> > This patch removes the abuse of discard for writing zeroes from
> > file-posix and instead adds a new function that uses interfaces that are
> > actually meant to deallocate and zero out at the same time. Only if
> > those fail, it falls back to zeroing out without unmap. We never fall
> > back to a discard operation any more that may or may not result in
> > zeros.
> >
> > Signed-off-by: Kevin Wolf <address@hidden>
> > ---
> > block/file-posix.c | 62
> > +++++++++++++++++++++++++++++++++++++++++-------------
> > 1 file changed, 47 insertions(+), 15 deletions(-)
> >
> > diff --git a/block/file-posix.c b/block/file-posix.c
> > index 60af4b3d51..9c66cd87d1 100644
> > --- a/block/file-posix.c
> > +++ b/block/file-posix.c
> > @@ -648,7 +648,7 @@ static int raw_open_common(BlockDriverState *bs, QDict
> > *options,
> > }
> > #endif
> >
> > - bs->supported_zero_flags = s->discard_zeroes ? BDRV_REQ_MAY_UNMAP : 0;
> > + bs->supported_zero_flags = BDRV_REQ_MAY_UNMAP;
> > ret = 0;
> > fail:
> > if (filename && (bdrv_flags & BDRV_O_TEMPORARY)) {
> > @@ -1487,6 +1487,38 @@ static ssize_t
> > handle_aiocb_write_zeroes(RawPosixAIOData *aiocb)
> > return -ENOTSUP;
> > }
> >
> > +static ssize_t handle_aiocb_write_zeroes_unmap(RawPosixAIOData *aiocb)
> > +{
> > + BDRVRawState *s = aiocb->bs->opaque;
> > + int ret;
> > +
> > + /* First try to write zeros and unmap at the same time */
> > +
> > +#ifdef CONFIG_FALLOCATE_PUNCH_HOLE
> > + ret = do_fallocate(s->fd, FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE,
> > + aiocb->aio_offset, aiocb->aio_nbytes);
> > + if (ret != -ENOTSUP) {
> >
>
> This fails with ENODEV on RHEL 7.5 when fd is a block device.
>
> The manual says:
>
> ENODEV fd does not refer to a regular file or a directory. (If fd
> is a pipe or FIFO, a different error results.)
do_fallocate() is a wrapper around fallocate() that handles EINTR and
translates a few errno values (including ENODEV) into a -ENOTSUP return
code.
Kevin
- Re: [Qemu-devel] [PATCH for-3.0] file-posix: Fix write_zeroes with unmap on block devices, (continued)
- Re: [Qemu-devel] [PATCH for-3.0] file-posix: Fix write_zeroes with unmap on block devices, Eric Blake, 2018/07/26
- Re: [Qemu-devel] [PATCH for-3.0] file-posix: Fix write_zeroes with unmap on block devices, Kevin Wolf, 2018/07/26
- Re: [Qemu-devel] [PATCH for-3.0] file-posix: Fix write_zeroes with unmap on block devices, Eric Blake, 2018/07/26
- Re: [Qemu-devel] [PATCH for-3.0] file-posix: Fix write_zeroes with unmap on block devices, Nir Soffer, 2018/07/26
- Re: [Qemu-devel] [PATCH for-3.0] file-posix: Fix write_zeroes with unmap on block devices, Kevin Wolf, 2018/07/26
- Re: [Qemu-devel] [PATCH for-3.0] file-posix: Fix write_zeroes with unmap on block devices, Nir Soffer, 2018/07/26
- Re: [Qemu-devel] [PATCH for-3.0] file-posix: Fix write_zeroes with unmap on block devices, Eric Blake, 2018/07/26
- Re: [Qemu-devel] [PATCH for-3.0] file-posix: Fix write_zeroes with unmap on block devices, Kevin Wolf, 2018/07/26
- Re: [Qemu-devel] [PATCH for-3.0] file-posix: Fix write_zeroes with unmap on block devices, Eric Blake, 2018/07/26
Re: [Qemu-devel] [Qemu-block] [PATCH for-3.0] file-posix: Fix write_zeroes with unmap on block devices, Nir Soffer, 2018/07/26
- Re: [Qemu-devel] [Qemu-block] [PATCH for-3.0] file-posix: Fix write_zeroes with unmap on block devices,
Kevin Wolf <=