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block: Convert .bdrv_truncate callback to coroutine_fn

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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>
This commit is contained in:
Kevin Wolf 2018-06-21 17:54:35 +02:00
parent ae5475e82f
commit 061ca8a368
16 changed files with 162 additions and 89 deletions
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12
block/file-posix.c
View file

@ -1878,8 +1878,8 @@ out:
return result;
}
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;
struct stat st;
@ -2625,7 +2625,7 @@ BlockDriver bdrv_file = {
.bdrv_io_unplug = raw_aio_unplug,
.bdrv_attach_aio_context = raw_aio_attach_aio_context,
.bdrv_truncate = raw_truncate,
.bdrv_co_truncate = raw_co_truncate,
.bdrv_getlength = raw_getlength,
.bdrv_get_info = raw_get_info,
.bdrv_get_allocated_file_size
@ -3105,7 +3105,7 @@ static BlockDriver bdrv_host_device = {
.bdrv_io_plug = raw_aio_plug,
.bdrv_io_unplug = raw_aio_unplug,
.bdrv_truncate = raw_truncate,
.bdrv_co_truncate = raw_co_truncate,
.bdrv_getlength = raw_getlength,
.bdrv_get_info = raw_get_info,
.bdrv_get_allocated_file_size
@ -3227,7 +3227,7 @@ static BlockDriver bdrv_host_cdrom = {
.bdrv_io_plug = raw_aio_plug,
.bdrv_io_unplug = raw_aio_unplug,
.bdrv_truncate = raw_truncate,
.bdrv_co_truncate = raw_co_truncate,
.bdrv_getlength = raw_getlength,
.has_variable_length = true,
.bdrv_get_allocated_file_size
@ -3357,7 +3357,7 @@ static BlockDriver bdrv_host_cdrom = {
.bdrv_io_plug = raw_aio_plug,
.bdrv_io_unplug = raw_aio_unplug,
.bdrv_truncate = raw_truncate,
.bdrv_co_truncate = raw_co_truncate,
.bdrv_getlength = raw_getlength,
.has_variable_length = true,
.bdrv_get_allocated_file_size