[Qemu-devel] [PATCH v2 0/2] block: Fix unaligned zero write

[Qemu-devel] [PATCH v2 0/2] block: Fix unaligned zero write

[Fam Zheng]

This fixes a segfault when doing unaligned zero write to an image that is 4k
aligned.

v2: Don't drop the unset of UNMAP flag. [Stefan, Peter]

Reproducer:

    $ (echo "open -o file.align=4k blkdebug::img"; echo "write -z 512 1024") | qemu-io

Fam Zheng (2):
  block: Fix unaligned zero write
  qemu-iotests: Test unaligned 4k zero write

 block.c                    | 45 ++++++++++++++++++++++++++++++++++++++------
 tests/qemu-iotests/033     | 47 +++++++++++++++++++++++++++++-----------------
 tests/qemu-iotests/033.out | 26 +++++++++++++++++++++++++
 3 files changed, 95 insertions(+), 23 deletions(-)

-- 
1.9.3

[Qemu-devel] [PATCH v2 1/2] block: Fix unaligned zero write

[Fam Zheng]

If the zero write is not aligned, bdrv_co_do_pwritev will segfault
because of accessing to the NULL qiov passed in by bdrv_co_write_zeroes.
Fix this by allocating a local qiov in bdrv_co_do_pwritev if the request
is not aligned. (In this case the padding iovs are necessary anyway, so
it doesn't hurt.)

Also add a check at the end of bdrv_co_do_pwritev to clear the zero flag
if padding is involved.

Signed-off-by: Fam Zheng <famz@redhat.com>
---
 block.c | 45 +++++++++++++++++++++++++++++++++++++++------
 1 file changed, 39 insertions(+), 6 deletions(-)

diff --git a/block.c b/block.c
index 0fe97de..f2f8ae7 100644
--- a/block.c
+++ b/block.c
@@ -3118,6 +3118,19 @@ out:
     return ret;
 }
 
+static inline uint64_t bdrv_get_align(BlockDriverState *bs)
+{
+    /* TODO Lift BDRV_SECTOR_SIZE restriction in BlockDriver interface */
+    return MAX(BDRV_SECTOR_SIZE, bs->request_alignment);
+}
+
+static inline bool bdrv_req_is_aligned(BlockDriverState *bs,
+                                       int64_t offset, size_t bytes)
+{
+    int64_t align = bdrv_get_align(bs);
+    return !(offset & (align - 1) || (bytes & (align - 1)));
+}
+
 /*
  * Handle a read request in coroutine context
  */
@@ -3128,8 +3141,7 @@ static int coroutine_fn bdrv_co_do_preadv(BlockDriverState *bs,
     BlockDriver *drv = bs->drv;
     BdrvTrackedRequest req;
 
-    /* TODO Lift BDRV_SECTOR_SIZE restriction in BlockDriver interface */
-    uint64_t align = MAX(BDRV_SECTOR_SIZE, bs->request_alignment);
+    uint64_t align = bdrv_get_align(bs);
     uint8_t *head_buf = NULL;
     uint8_t *tail_buf = NULL;
     QEMUIOVector local_qiov;
@@ -3371,8 +3383,7 @@ static int coroutine_fn bdrv_co_do_pwritev(BlockDriverState *bs,
     BdrvRequestFlags flags)
 {
     BdrvTrackedRequest req;
-    /* TODO Lift BDRV_SECTOR_SIZE restriction in BlockDriver interface */
-    uint64_t align = MAX(BDRV_SECTOR_SIZE, bs->request_alignment);
+    uint64_t align = bdrv_get_align(bs);
     uint8_t *head_buf = NULL;
     uint8_t *tail_buf = NULL;
     QEMUIOVector local_qiov;
@@ -3471,6 +3482,10 @@ static int coroutine_fn bdrv_co_do_pwritev(BlockDriverState *bs,
         bytes = ROUND_UP(bytes, align);
     }
 
+    if (use_local_qiov) {
+        /* Local buffer may have non-zero data. */
+        flags &= ~BDRV_REQ_ZERO_WRITE;
+    }
     ret = bdrv_aligned_pwritev(bs, &req, offset, bytes,
                                use_local_qiov ? &local_qiov : qiov,
                                flags);
@@ -3511,14 +3526,32 @@ int coroutine_fn bdrv_co_write_zeroes(BlockDriverState *bs,
                                       int64_t sector_num, int nb_sectors,
                                       BdrvRequestFlags flags)
 {
+    int ret;
+
     trace_bdrv_co_write_zeroes(bs, sector_num, nb_sectors, flags);
 
     if (!(bs->open_flags & BDRV_O_UNMAP)) {
         flags &= ~BDRV_REQ_MAY_UNMAP;
     }
+    if (bdrv_req_is_aligned(bs, sector_num << BDRV_SECTOR_BITS,
+                            nb_sectors << BDRV_SECTOR_BITS)) {
+        ret = bdrv_co_do_writev(bs, sector_num, nb_sectors, NULL,
+                                BDRV_REQ_ZERO_WRITE | flags);
+    } else {
+        uint8_t *buf;
+        QEMUIOVector local_qiov;
+        size_t bytes = nb_sectors << BDRV_SECTOR_BITS;
 
-    return bdrv_co_do_writev(bs, sector_num, nb_sectors, NULL,
-                             BDRV_REQ_ZERO_WRITE | flags);
+        buf = qemu_memalign(bdrv_opt_mem_align(bs), bytes);
+        memset(buf, 0, bytes);
+        qemu_iovec_init(&local_qiov, 1);
+        qemu_iovec_add(&local_qiov, buf, bytes);
+
+        ret = bdrv_co_do_writev(bs, sector_num, nb_sectors, &local_qiov,
+                                BDRV_REQ_ZERO_WRITE | flags);
+        qemu_vfree(buf);
+    }
+    return ret;
 }
 
 /**
-- 
1.9.3

[Qemu-devel] [PATCH v2 2/2] qemu-iotests: Test unaligned 4k zero write

[Fam Zheng]

Signed-off-by: Fam Zheng <famz@redhat.com>
---
 tests/qemu-iotests/033     | 47 +++++++++++++++++++++++++++++-----------------
 tests/qemu-iotests/033.out | 26 +++++++++++++++++++++++++
 2 files changed, 56 insertions(+), 17 deletions(-)

diff --git a/tests/qemu-iotests/033 b/tests/qemu-iotests/033
index ea3351c..4008f10 100755
--- a/tests/qemu-iotests/033
+++ b/tests/qemu-iotests/033
@@ -46,26 +46,39 @@ _supported_os Linux
 size=128M
 _make_test_img $size
 
-echo
-echo "== preparing image =="
-$QEMU_IO -c "write -P 0xa 0x200 0x400" "$TEST_IMG" | _filter_qemu_io
-$QEMU_IO -c "write -P 0xa 0x20000 0x600" "$TEST_IMG" | _filter_qemu_io
-$QEMU_IO -c "write -z 0x400 0x20000" "$TEST_IMG" | _filter_qemu_io
+do_test()
+{
+	local align=$1
+	local iocmd=$2
+	local img=$3
+	{
+		echo "open -o driver=$IMGFMT,file.align=$align blkdebug::$img"
+		echo $iocmd
+	} | $QEMU_IO
+}
 
-echo
-echo "== verifying patterns (1) =="
-$QEMU_IO -c "read -P 0xa 0x200 0x200" "$TEST_IMG" | _filter_qemu_io
-$QEMU_IO -c "read -P 0x0 0x400 0x20000" "$TEST_IMG" | _filter_qemu_io
-$QEMU_IO -c "read -P 0xa 0x20400 0x200" "$TEST_IMG" | _filter_qemu_io
+for align in 512 4k; do
+	echo
+	echo "== preparing image =="
+	do_test $align "write -P 0xa 0x200 0x400" "$TEST_IMG" | _filter_qemu_io
+	do_test $align "write -P 0xa 0x20000 0x600" "$TEST_IMG" | _filter_qemu_io
+	do_test $align "write -z 0x400 0x20000" "$TEST_IMG" | _filter_qemu_io
 
-echo
-echo "== rewriting zeroes =="
-$QEMU_IO -c "write -P 0xb 0x10000 0x10000" "$TEST_IMG" | _filter_qemu_io
-$QEMU_IO -c "write -z 0x10000 0x10000" "$TEST_IMG" | _filter_qemu_io
+	echo
+	echo "== verifying patterns (1) =="
+	do_test $align "read -P 0xa 0x200 0x200" "$TEST_IMG" | _filter_qemu_io
+	do_test $align "read -P 0x0 0x400 0x20000" "$TEST_IMG" | _filter_qemu_io
+	do_test $align "read -P 0xa 0x20400 0x200" "$TEST_IMG" | _filter_qemu_io
 
-echo
-echo "== verifying patterns (2) =="
-$QEMU_IO -c "read -P 0x0 0x400 0x20000" "$TEST_IMG" | _filter_qemu_io
+	echo
+	echo "== rewriting zeroes =="
+	do_test $align "write -P 0xb 0x10000 0x10000" "$TEST_IMG" | _filter_qemu_io
+	do_test $align "write -z 0x10000 0x10000" "$TEST_IMG" | _filter_qemu_io
+
+	echo
+	echo "== verifying patterns (2) =="
+	do_test $align "read -P 0x0 0x400 0x20000" "$TEST_IMG" | _filter_qemu_io
+done
 
 # success, all done
 echo "*** done"
diff --git a/tests/qemu-iotests/033.out b/tests/qemu-iotests/033.out
index 41475ee..305949f 100644
--- a/tests/qemu-iotests/033.out
+++ b/tests/qemu-iotests/033.out
@@ -26,4 +26,30 @@ wrote 65536/65536 bytes at offset 65536
 == verifying patterns (2) ==
 read 131072/131072 bytes at offset 1024
 128 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
+
+== preparing image ==
+wrote 1024/1024 bytes at offset 512
+1 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
+wrote 1536/1536 bytes at offset 131072
+1.500 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
+wrote 131072/131072 bytes at offset 1024
+128 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
+
+== verifying patterns (1) ==
+read 512/512 bytes at offset 512
+512 bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
+read 131072/131072 bytes at offset 1024
+128 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
+read 512/512 bytes at offset 132096
+512 bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
+
+== rewriting zeroes ==
+wrote 65536/65536 bytes at offset 65536
+64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
+wrote 65536/65536 bytes at offset 65536
+64 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
+
+== verifying patterns (2) ==
+read 131072/131072 bytes at offset 1024
+128 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 *** done
-- 
1.9.3

Re: [Qemu-devel] [PATCH v2 0/2] block: Fix unaligned zero write

[Stefan Hajnoczi]

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On Tue, Mar 24, 2015 at 09:23:48AM +0800, Fam Zheng wrote:
> This fixes a segfault when doing unaligned zero write to an image that is 4k
> aligned.
> 
> v2: Don't drop the unset of UNMAP flag. [Stefan, Peter]
> 
> Reproducer:
> 
>     $ (echo "open -o file.align=4k blkdebug::img"; echo "write -z 512 1024") | qemu-io
> 
> Fam Zheng (2):
>   block: Fix unaligned zero write
>   qemu-iotests: Test unaligned 4k zero write
> 
>  block.c                    | 45 ++++++++++++++++++++++++++++++++++++++------
>  tests/qemu-iotests/033     | 47 +++++++++++++++++++++++++++++-----------------
>  tests/qemu-iotests/033.out | 26 +++++++++++++++++++++++++
>  3 files changed, 95 insertions(+), 23 deletions(-)

Thanks, applied to my block tree:
https://github.com/stefanha/qemu/commits/block

Stefan

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