13.10.2019 23:48, Alberto Garcia wrote:
> The BDRV_REQ_NO_FALLBACK flag means that an operation should only be
> performed if it can be offloaded or otherwise performed efficiently.
As I know, BDRV_REQ_NO_FALLBACK is for write-zeros only, not about offloading..
>
> However a misaligned write request requires a RMW so we should return
> an error and let the caller decide how to proceed.
Because we can finish up with trying to to normal write (not write_zero) with
BDRV_REQ_NO_FALLBACK flag, which is forbidden for bdrv_driver_pwritev, as it's
shown in assertion below.
>
> This hits an assertion since commit c8bb23cbdb if the required
> alignment is larger than the cluster size:
>
> qemu-img create -f qcow2 -o cluster_size=2k img.qcow2 4G
> qemu-io -c "open -o driver=qcow2,file.align=4k blkdebug::img.qcow2" \
> -c 'write 0 512'
> qemu-io: block/io.c:1127: bdrv_driver_pwritev: Assertion `!(flags &
> BDRV_REQ_NO_FALLBACK)' failed.
> Aborted
>
> Signed-off-by: Alberto Garcia <be...@igalia.com>
> ---
> block/io.c | 6 +++++
> tests/qemu-iotests/268 | 55 ++++++++++++++++++++++++++++++++++++++
> tests/qemu-iotests/268.out | 7 +++++
> tests/qemu-iotests/group | 1 +
> 4 files changed, 69 insertions(+)
> create mode 100755 tests/qemu-iotests/268
> create mode 100644 tests/qemu-iotests/268.out
>
> diff --git a/block/io.c b/block/io.c
> index 4f9ee97c2b..c5d4d029da 100644
> --- a/block/io.c
> +++ b/block/io.c
> @@ -2071,6 +2071,12 @@ int coroutine_fn bdrv_co_pwritev_part(BdrvChild *child,
> return ret;
> }
>
> + /* If the request is misaligned then we can't make it efficient */
> + if (((offset & (align - 1)) || (bytes & (align - 1))) &&
> + (flags & BDRV_REQ_NO_FALLBACK)) {
> + return -ENOTSUP;
> + }
> +
So, if BDRV_REQ_NO_FALLBACK is only for write zeros, most correct place for
this check
is bdrv_co_do_zero_pwritev().. But it's OK as is too.
Not long ago such checks was fixed to be QEMU_IS_ALIGNED, so with it used
instead:
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsement...@virtuozzo.com>
> bdrv_inc_in_flight(bs);
> /*
> * Align write if necessary by performing a read-modify-write cycle.
> diff --git a/tests/qemu-iotests/268 b/tests/qemu-iotests/268
> new file mode 100755
> index 0000000000..895f6e593f
> --- /dev/null
> +++ b/tests/qemu-iotests/268
> @@ -0,0 +1,55 @@
> +#!/usr/bin/env bash
> +#
> +# Test write request with required alignment larger than the cluster size
> +#
> +# Copyright (C) 2019 Igalia, S.L.
> +# Author: Alberto Garcia <be...@igalia.com>
> +#
> +# This program is free software; you can redistribute it and/or modify
> +# it under the terms of the GNU General Public License as published by
> +# the Free Software Foundation; either version 2 of the License, or
> +# (at your option) any later version.
> +#
> +# This program is distributed in the hope that it will be useful,
> +# but WITHOUT ANY WARRANTY; without even the implied warranty of
> +# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
> +# GNU General Public License for more details.
> +#
> +# You should have received a copy of the GNU General Public License
> +# along with this program. If not, see <http://www.gnu.org/licenses/>.
> +#
> +
> +# creator
> +owner=be...@igalia.com
> +
> +seq=`basename $0`
> +echo "QA output created by $seq"
> +
> +status=1 # failure is the default!
> +
> +_cleanup()
> +{
> + _cleanup_test_img
> +}
> +trap "_cleanup; exit \$status" 0 1 2 3 15
> +
> +# get standard environment, filters and checks
> +. ./common.rc
> +. ./common.filter
> +
> +_supported_fmt qcow2
> +_supported_proto file
> +
> +echo
> +echo "== Required alignment larger than cluster size =="
> +
> +CLUSTER_SIZE=2k _make_test_img 1M
> +# Since commit c8bb23cbdb writing to an allocated cluster fills the
> +# empty COW areas with bdrv_write_zeroes(flags=BDRV_REQ_NO_FALLBACK)
> +$QEMU_IO -c "open -o driver=$IMGFMT,file.align=4k blkdebug::$TEST_IMG" \
> + -c "write 0 512" | _filter_qemu_io
> +
> +# success, all done
> +echo "*** done"
> +rm -f $seq.full
> +status=0
> diff --git a/tests/qemu-iotests/268.out b/tests/qemu-iotests/268.out
> new file mode 100644
> index 0000000000..2ed6c68529
> --- /dev/null
> +++ b/tests/qemu-iotests/268.out
> @@ -0,0 +1,7 @@
> +QA output created by 268
> +
> +== Required alignment larger than cluster size ==
> +Formatting 'TEST_DIR/t.IMGFMT', fmt=IMGFMT size=1048576
> +wrote 512/512 bytes at offset 0
> +512 bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
> +*** done
> diff --git a/tests/qemu-iotests/group b/tests/qemu-iotests/group
> index 5805a79d9e..4c861f7eed 100644
> --- a/tests/qemu-iotests/group
> +++ b/tests/qemu-iotests/group
> @@ -278,3 +278,4 @@
> 265 rw auto quick
> 266 rw quick
> 267 rw auto quick snapshot
> +268 rw auto quick
>
--
Best regards,
Vladimir
