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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
Download patch file Download diff file Expand all files Collapse all files

74
block/qcow2.c
View file

@ -2543,15 +2543,12 @@ static void coroutine_fn preallocate_co(void *opaque)
BlockDriverState *bs = params->bs;
uint64_t offset = params->offset;
uint64_t new_length = params->new_length;
BDRVQcow2State *s = bs->opaque;
uint64_t bytes;
uint64_t host_offset = 0;
unsigned int cur_bytes;
int ret;
QCowL2Meta *meta;
qemu_co_mutex_lock(&s->lock);
assert(offset <= new_length);
bytes = new_length - offset;
@ -2604,7 +2601,6 @@ static void coroutine_fn preallocate_co(void *opaque)
ret = 0;
done:
qemu_co_mutex_unlock(&s->lock);
params->ret = ret;
}
@ -3041,7 +3037,11 @@ qcow2_co_create(BlockdevCreateOptions *create_options, Error **errp)
/* And if we're supposed to preallocate metadata, do that now */
if (qcow2_opts->preallocation != PREALLOC_MODE_OFF) {
BDRVQcow2State *s = blk_bs(blk)->opaque;
qemu_co_mutex_lock(&s->lock);
ret = preallocate(blk_bs(blk), 0, qcow2_opts->size);
qemu_co_mutex_unlock(&s->lock);
if (ret < 0) {
error_setg_errno(errp, -ret, "Could not preallocate metadata");
goto out;
@ -3437,8 +3437,8 @@ fail:
return ret;
}
static int qcow2_truncate(BlockDriverState *bs, int64_t offset,
PreallocMode prealloc, Error **errp)
static int coroutine_fn qcow2_co_truncate(BlockDriverState *bs, int64_t offset,
PreallocMode prealloc, Error **errp)
{
BDRVQcow2State *s = bs->opaque;
uint64_t old_length;
@ -3458,17 +3458,21 @@ static int qcow2_truncate(BlockDriverState *bs, int64_t offset,
return -EINVAL;
}
qemu_co_mutex_lock(&s->lock);
/* cannot proceed if image has snapshots */
if (s->nb_snapshots) {
error_setg(errp, "Can't resize an image which has snapshots");
return -ENOTSUP;
ret = -ENOTSUP;
goto fail;
}
/* cannot proceed if image has bitmaps */
if (s->nb_bitmaps) {
/* TODO: resize bitmaps in the image */
error_setg(errp, "Can't resize an image which has bitmaps");
return -ENOTSUP;
ret = -ENOTSUP;
goto fail;
}
old_length = bs->total_sectors * 512;
@ -3479,7 +3483,8 @@ static int qcow2_truncate(BlockDriverState *bs, int64_t offset,
if (prealloc != PREALLOC_MODE_OFF) {
error_setg(errp,
"Preallocation can't be used for shrinking an image");
return -EINVAL;
ret = -EINVAL;
goto fail;
}
ret = qcow2_cluster_discard(bs, ROUND_UP(offset, s->cluster_size),
@ -3488,40 +3493,42 @@ static int qcow2_truncate(BlockDriverState *bs, int64_t offset,
QCOW2_DISCARD_ALWAYS, true);
if (ret < 0) {
error_setg_errno(errp, -ret, "Failed to discard cropped clusters");
return ret;
goto fail;
}
ret = qcow2_shrink_l1_table(bs, new_l1_size);
if (ret < 0) {
error_setg_errno(errp, -ret,
"Failed to reduce the number of L2 tables");
return ret;
goto fail;
}
ret = qcow2_shrink_reftable(bs);
if (ret < 0) {
error_setg_errno(errp, -ret,
"Failed to discard unused refblocks");
return ret;
goto fail;
}
old_file_size = bdrv_getlength(bs->file->bs);
if (old_file_size < 0) {
error_setg_errno(errp, -old_file_size,
"Failed to inquire current file length");
return old_file_size;
ret = old_file_size;
goto fail;
}
last_cluster = qcow2_get_last_cluster(bs, old_file_size);
if (last_cluster < 0) {
error_setg_errno(errp, -last_cluster,
"Failed to find the last cluster");
return last_cluster;
ret = last_cluster;
goto fail;
}
if ((last_cluster + 1) * s->cluster_size < old_file_size) {
Error *local_err = NULL;
bdrv_truncate(bs->file, (last_cluster + 1) * s->cluster_size,
PREALLOC_MODE_OFF, &local_err);
bdrv_co_truncate(bs->file, (last_cluster + 1) * s->cluster_size,
PREALLOC_MODE_OFF, &local_err);
if (local_err) {
warn_reportf_err(local_err,
"Failed to truncate the tail of the image: ");
@ -3531,7 +3538,7 @@ static int qcow2_truncate(BlockDriverState *bs, int64_t offset,
ret = qcow2_grow_l1_table(bs, new_l1_size, true);
if (ret < 0) {
error_setg_errno(errp, -ret, "Failed to grow the L1 table");
return ret;
goto fail;
}
}
@ -3543,7 +3550,7 @@ static int qcow2_truncate(BlockDriverState *bs, int64_t offset,
ret = preallocate(bs, old_length, offset);
if (ret < 0) {
error_setg_errno(errp, -ret, "Preallocation failed");
return ret;
goto fail;
}
break;
@ -3559,7 +3566,8 @@ static int qcow2_truncate(BlockDriverState *bs, int64_t offset,
if (old_file_size < 0) {
error_setg_errno(errp, -old_file_size,
"Failed to inquire current file length");
return old_file_size;
ret = old_file_size;
goto fail;
}
old_file_size = ROUND_UP(old_file_size, s->cluster_size);
@ -3589,7 +3597,8 @@ static int qcow2_truncate(BlockDriverState *bs, int64_t offset,
if (allocation_start < 0) {
error_setg_errno(errp, -allocation_start,
"Failed to resize refcount structures");
return allocation_start;
ret = allocation_start;
goto fail;
}
clusters_allocated = qcow2_alloc_clusters_at(bs, allocation_start,
@ -3597,7 +3606,8 @@ static int qcow2_truncate(BlockDriverState *bs, int64_t offset,
if (clusters_allocated < 0) {
error_setg_errno(errp, -clusters_allocated,
"Failed to allocate data clusters");
return clusters_allocated;
ret = clusters_allocated;
goto fail;
}
assert(clusters_allocated == nb_new_data_clusters);
@ -3605,13 +3615,13 @@ static int qcow2_truncate(BlockDriverState *bs, int64_t offset,
/* Allocate the data area */
new_file_size = allocation_start +
nb_new_data_clusters * s->cluster_size;
ret = bdrv_truncate(bs->file, new_file_size, prealloc, errp);
ret = bdrv_co_truncate(bs->file, new_file_size, prealloc, errp);
if (ret < 0) {
error_prepend(errp, "Failed to resize underlying file: ");
qcow2_free_clusters(bs, allocation_start,
nb_new_data_clusters * s->cluster_size,
QCOW2_DISCARD_OTHER);
return ret;
goto fail;
}
/* Create the necessary L2 entries */
@ -3634,7 +3644,7 @@ static int qcow2_truncate(BlockDriverState *bs, int64_t offset,
qcow2_free_clusters(bs, host_offset,
nb_new_data_clusters * s->cluster_size,
QCOW2_DISCARD_OTHER);
return ret;
goto fail;
}
guest_offset += nb_clusters * s->cluster_size;
@ -3650,11 +3660,11 @@ static int qcow2_truncate(BlockDriverState *bs, int64_t offset,
if (prealloc != PREALLOC_MODE_OFF) {
/* Flush metadata before actually changing the image size */
ret = bdrv_flush(bs);
ret = qcow2_write_caches(bs);
if (ret < 0) {
error_setg_errno(errp, -ret,
"Failed to flush the preallocated area to disk");
return ret;
goto fail;
}
}
@ -3664,11 +3674,14 @@ static int qcow2_truncate(BlockDriverState *bs, int64_t offset,
&offset, sizeof(uint64_t));
if (ret < 0) {
error_setg_errno(errp, -ret, "Failed to update the image size");
return ret;
goto fail;
}
s->l1_vm_state_index = new_l1_size;
return 0;
ret = 0;
fail:
qemu_co_mutex_unlock(&s->lock);
return ret;
}
/* XXX: put compressed sectors first, then all the cluster aligned
@ -3692,7 +3705,8 @@ qcow2_co_pwritev_compressed(BlockDriverState *bs, uint64_t offset,
if (cluster_offset < 0) {
return cluster_offset;
}
return bdrv_truncate(bs->file, cluster_offset, PREALLOC_MODE_OFF, NULL);
return bdrv_co_truncate(bs->file, cluster_offset, PREALLOC_MODE_OFF,
NULL);
}
if (offset_into_cluster(s, offset)) {
@ -4696,7 +4710,7 @@ BlockDriver bdrv_qcow2 = {
.bdrv_co_pdiscard = qcow2_co_pdiscard,
.bdrv_co_copy_range_from = qcow2_co_copy_range_from,
.bdrv_co_copy_range_to = qcow2_co_copy_range_to,
.bdrv_truncate = qcow2_truncate,
.bdrv_co_truncate = qcow2_co_truncate,
.bdrv_co_pwritev_compressed = qcow2_co_pwritev_compressed,
.bdrv_make_empty = qcow2_make_empty,