block: Convert .bdrv_truncate callback to coroutine_fn
bdrv_truncate() is an operation that can block (even for a quite long
time, depending on the PreallocMode) in I/O paths that shouldn't block.
Convert it to a coroutine_fn so that we have the infrastructure for
drivers to make their .bdrv_co_truncate implementation asynchronous.
This change could potentially introduce new race conditions because
bdrv_truncate() isn't necessarily executed atomically any more. Whether
this is a problem needs to be evaluated for each block driver that
supports truncate:
* file-posix/win32, gluster, iscsi, nfs, rbd, ssh, sheepdog: The
protocol drivers are trivially safe because they don't actually yield
yet, so there is no change in behaviour.
* copy-on-read, crypto, raw-format: Essentially just filter drivers that
pass the request to a child node, no problem.
* qcow2: The implementation modifies metadata, so it needs to hold
s->lock to be safe with concurrent I/O requests. In order to avoid
double locking, this requires pulling the locking out into
preallocate_co() and using qcow2_write_caches() instead of
bdrv_flush().
* qed: Does a single header update, this is fine without locking.
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
diff --git a/block/raw-format.c b/block/raw-format.c
index f2e468d..b78da56 100644
--- a/block/raw-format.c
+++ b/block/raw-format.c
@@ -366,8 +366,8 @@
}
}
-static int raw_truncate(BlockDriverState *bs, int64_t offset,
- PreallocMode prealloc, Error **errp)
+static int coroutine_fn raw_co_truncate(BlockDriverState *bs, int64_t offset,
+ PreallocMode prealloc, Error **errp)
{
BDRVRawState *s = bs->opaque;
@@ -383,7 +383,7 @@
s->size = offset;
offset += s->offset;
- return bdrv_truncate(bs->file, offset, prealloc, errp);
+ return bdrv_co_truncate(bs->file, offset, prealloc, errp);
}
static void raw_eject(BlockDriverState *bs, bool eject_flag)
@@ -545,7 +545,7 @@
.bdrv_co_block_status = &raw_co_block_status,
.bdrv_co_copy_range_from = &raw_co_copy_range_from,
.bdrv_co_copy_range_to = &raw_co_copy_range_to,
- .bdrv_truncate = &raw_truncate,
+ .bdrv_co_truncate = &raw_co_truncate,
.bdrv_getlength = &raw_getlength,
.has_variable_length = true,
.bdrv_measure = &raw_measure,
