qcow2: Implement .bdrv_co_preadv()

Reading from qcow2 images is now byte granularity.

Most of the affected code in qcow2 actually gets simpler with this
change. The only exception is encryption, which is fixed on 512 bytes
blocks; in order to keep this working, bs->request_alignment is set for
encrypted images.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>

1 files changed, 12 insertions, 15 deletions

diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c
index a59fb3493c..277764f36c 100644
--- a/block/qcow2-cluster.c
+++ b/block/qcow2-cluster.c
@@ -424,7 +424,8 @@ static int coroutine_fn copy_sectors(BlockDriverState *bs,
      * interface.  This avoids double I/O throttling and request tracking,
      * which can lead to deadlock when block layer copy-on-read is enabled.
      */
-    ret = bs->drv->bdrv_co_readv(bs, start_sect + n_start, n, &qiov);
+    ret = bs->drv->bdrv_co_preadv(bs, (start_sect + n_start) * BDRV_SECTOR_SIZE,
+                                  n * BDRV_SECTOR_SIZE, &qiov, 0);
     if (ret < 0) {
         goto out;
     }
@@ -464,19 +465,21 @@ out:
 /*
  * get_cluster_offset
  *
- * For a given offset of the disk image, find the cluster offset in
- * qcow2 file. The offset is stored in *cluster_offset.
+ * For a given offset of the virtual disk, find the cluster type and offset in
+ * the qcow2 file. The offset is stored in *cluster_offset.
  *
- * on entry, *num is the number of contiguous sectors we'd like to
- * access following offset.
+ * On entry, *bytes is the maximum number of contiguous bytes starting at
+ * offset that we are interested in.
  *
- * on exit, *num is the number of contiguous sectors we can read.
+ * On exit, *bytes is the number of bytes starting at offset that have the same
+ * cluster type and (if applicable) are stored contiguously in the image file.
+ * Compressed clusters are always returned one by one.
  *
  * Returns the cluster type (QCOW2_CLUSTER_*) on success, -errno in error
  * cases.
  */
 int qcow2_get_cluster_offset(BlockDriverState *bs, uint64_t offset,
-    int *num, uint64_t *cluster_offset)
+                             unsigned int *bytes, uint64_t *cluster_offset)
 {
     BDRVQcow2State *s = bs->opaque;
     unsigned int l2_index;
@@ -485,13 +488,9 @@ int qcow2_get_cluster_offset(BlockDriverState *bs, uint64_t offset,
     unsigned int offset_in_cluster, nb_clusters;
     uint64_t bytes_available, bytes_needed;
     int ret;
-    unsigned int bytes;
-
-    assert(*num <= BDRV_REQUEST_MAX_SECTORS);
-    bytes = *num * BDRV_SECTOR_SIZE;
 
     offset_in_cluster = offset_into_cluster(s, offset);
-    bytes_needed = (uint64_t) bytes + offset_in_cluster;
+    bytes_needed = (uint64_t) *bytes + offset_in_cluster;
 
     l1_bits = s->l2_bits + s->cluster_bits;
 
@@ -595,9 +594,7 @@ out:
         bytes_available = bytes_needed;
     }
 
-    bytes = bytes_available - offset_in_cluster;
-    assert((bytes & (BDRV_SECTOR_SIZE - 1)) == 0);
-    *num = bytes >> BDRV_SECTOR_BITS;
+    *bytes = bytes_available - offset_in_cluster;
 
     return ret;