[Qemu-devel] [PATCH 5/8] qcow: Switch to a byte-based driver

[Eric Blake <eblake@redhat.com>]

We are gradually moving away from sector-based interfaces, towards
byte-based.  The qcow driver is now ready to fully utilize the
byte-based callback interface, as long as we override the default
alignment to still be 512 (needed at least for encryption, but
easier to do everywhere than to audit which sub-sector requests
are handled correctly).

Signed-off-by: Eric Blake <eblake@redhat.com>
---
 block/qcow.c | 35 ++++++++++++++++++++---------------
 1 file changed, 20 insertions(+), 15 deletions(-)

diff --git a/block/qcow.c b/block/qcow.c
index ea81a3bf87d..75fd75cf976 100644
--- a/block/qcow.c
+++ b/block/qcow.c
@@ -69,7 +69,6 @@ typedef struct QCowHeader {
 typedef struct BDRVQcowState {
     int cluster_bits;
     int cluster_size;
-    int cluster_sectors;
     int l2_bits;
     int l2_size;
     unsigned int l1_size;
@@ -235,7 +234,6 @@ static int qcow_open(BlockDriverState *bs, QDict *options, int flags,
     }
     s->cluster_bits = header.cluster_bits;
     s->cluster_size = 1 << s->cluster_bits;
-    s->cluster_sectors = 1 << (s->cluster_bits - 9);
     s->l2_bits = header.l2_bits;
     s->l2_size = 1 << s->l2_bits;
     bs->total_sectors = header.size / 512;
@@ -612,8 +610,18 @@ static int decompress_cluster(BlockDriverState *bs, uint64_t cluster_offset)
     return 0;
 }

-static coroutine_fn int qcow_co_readv(BlockDriverState *bs, int64_t sector_num,
-                         int nb_sectors, QEMUIOVector *qiov)
+static void qcow_refresh_limits(BlockDriverState *bs, Error **errp)
+{
+    /* At least encrypted images require 512-byte alignment. Apply the
+     * limit universally, rather than just on encrypted images, as
+     * it's easier to let the block layer handle rounding than to
+     * audit this code further. */
+    bs->bl.request_alignment = BDRV_SECTOR_SIZE;
+}
+
+static coroutine_fn int qcow_co_preadv(BlockDriverState *bs, uint64_t offset,
+                                       uint64_t bytes, QEMUIOVector *qiov,
+                                       int flags)
 {
     BDRVQcowState *s = bs->opaque;
     int index_in_cluster;
@@ -623,9 +631,8 @@ static coroutine_fn int qcow_co_readv(BlockDriverState *bs, int64_t sector_num,
     QEMUIOVector hd_qiov;
     uint8_t *buf;
     void *orig_buf;
-    int64_t offset = sector_num << BDRV_SECTOR_BITS;
-    int64_t bytes = nb_sectors << BDRV_SECTOR_BITS;

+    assert(!flags);
     if (qiov->niov > 1) {
         buf = orig_buf = qemu_try_blockalign(bs, qiov->size);
         if (buf == NULL) {
@@ -718,9 +725,9 @@ static coroutine_fn int qcow_co_readv(BlockDriverState *bs, int64_t sector_num,
     return ret;
 }

-static coroutine_fn int qcow_co_writev(BlockDriverState *bs, int64_t sector_num,
-                                       int nb_sectors, QEMUIOVector *qiov,
-                                       int flags)
+static coroutine_fn int qcow_co_pwritev(BlockDriverState *bs, uint64_t offset,
+                                        uint64_t bytes, QEMUIOVector *qiov,
+                                        int flags)
 {
     BDRVQcowState *s = bs->opaque;
     int index_in_cluster;
@@ -730,8 +737,6 @@ static coroutine_fn int qcow_co_writev(BlockDriverState *bs, int64_t sector_num,
     QEMUIOVector hd_qiov;
     uint8_t *buf;
     void *orig_buf;
-    int64_t offset = sector_num << BDRV_SECTOR_BITS;
-    int64_t bytes = nb_sectors << BDRV_SECTOR_BITS;

     assert(!flags);
     s->cluster_cache_offset = -1; /* disable compressed cache */
@@ -1108,8 +1113,7 @@ qcow_co_pwritev_compressed(BlockDriverState *bs, uint64_t offset,

     if (ret != Z_STREAM_END || out_len >= s->cluster_size) {
         /* could not compress: write normal cluster */
-        ret = qcow_co_writev(bs, offset >> BDRV_SECTOR_BITS,
-                             bytes >> BDRV_SECTOR_BITS, qiov, 0);
+        ret = qcow_co_pwritev(bs, offset, bytes, qiov, 0);
         if (ret < 0) {
             goto fail;
         }
@@ -1194,9 +1198,10 @@ static BlockDriver bdrv_qcow = {
     .bdrv_co_create_opts    = qcow_co_create_opts,
     .bdrv_has_zero_init     = bdrv_has_zero_init_1,
     .supports_backing       = true,
+    .bdrv_refresh_limits    = qcow_refresh_limits,

-    .bdrv_co_readv          = qcow_co_readv,
-    .bdrv_co_writev         = qcow_co_writev,
+    .bdrv_co_preadv         = qcow_co_preadv,
+    .bdrv_co_pwritev        = qcow_co_pwritev,
     .bdrv_co_block_status   = qcow_co_block_status,

     .bdrv_make_empty        = qcow_make_empty,
-- 
2.14.3