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| author | Kevin Wolf <kwolf@redhat.com> | 2009-10-08 15:02:08 +0200 |
|---|---|---|
| committer | Anthony Liguori <aliguori@us.ibm.com> | 2009-10-15 09:32:04 -0500 |
| commit | ef845c3bf421290153154635dc18eaa677cecb43 (patch) | |
| tree | ba19ca2a96584e32e0fa08bcbea93ea46232507e /block/qcow2-cluster.c | |
| parent | be8b28a94020fd564c9bb9f0094e8c3ff45c0771 (diff) | |
| download | qemu-ef845c3bf421290153154635dc18eaa677cecb43.zip qemu-ef845c3bf421290153154635dc18eaa677cecb43.tar.gz qemu-ef845c3bf421290153154635dc18eaa677cecb43.tar.bz2 | |
qcow2: Bring synchronous read/write back to life
When the synchronous read and write functions were dropped, they were replaced
by generic emulation functions. Unfortunately, these emulation functions don't
provide the same semantics as the original functions did.
The original bdrv_read would mean that we read some data synchronously and that
we won't be interrupted during this read. The latter assumption is no longer
true with the emulation function which needs to use qemu_aio_poll and therefore
allows the callback of any other concurrent AIO request to be run during the
read. Which in turn means that (meta)data read earlier could have changed and
be invalid now. qcow2 is not prepared to work in this way and it's just scary
how many places there are where other requests could run.
I'm not sure yet where exactly it breaks, but you'll see breakage with virtio
on qcow2 with a backing file. Providing synchronous functions again fixes the
problem for me.
Patchworks-ID: 35437
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
Diffstat (limited to 'block/qcow2-cluster.c')
| -rw-r--r-- | block/qcow2-cluster.c | 6 |
1 files changed, 3 insertions, 3 deletions
diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c index e444e53..a7de820 100644 --- a/block/qcow2-cluster.c +++ b/block/qcow2-cluster.c @@ -306,8 +306,8 @@ void qcow2_encrypt_sectors(BDRVQcowState *s, int64_t sector_num, } -static int qcow_read(BlockDriverState *bs, int64_t sector_num, - uint8_t *buf, int nb_sectors) +int qcow2_read(BlockDriverState *bs, int64_t sector_num, uint8_t *buf, + int nb_sectors) { BDRVQcowState *s = bs->opaque; int ret, index_in_cluster, n, n1; @@ -358,7 +358,7 @@ static int copy_sectors(BlockDriverState *bs, uint64_t start_sect, n = n_end - n_start; if (n <= 0) return 0; - ret = qcow_read(bs, start_sect + n_start, s->cluster_data, n); + ret = qcow2_read(bs, start_sect + n_start, s->cluster_data, n); if (ret < 0) return ret; if (s->crypt_method) { |