block: Convert bdrv_pread(v) to BdrvChild

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Acked-by: Stefan Hajnoczi <stefanha@redhat.com>

18 files changed, 108 insertions, 101 deletions

diff --git a/block.c b/block.c
index 7603a0b5db..823ff1d7ab 100644
--- a/block.c
+++ b/block.c
@@ -536,9 +536,10 @@ BlockDriver *bdrv_probe_all(const uint8_t *buf, int buf_size,
     return drv;
 }
 
-static int find_image_format(BlockDriverState *bs, const char *filename,
+static int find_image_format(BdrvChild *file, const char *filename,
                              BlockDriver **pdrv, Error **errp)
 {
+    BlockDriverState *bs = file->bs;
     BlockDriver *drv;
     uint8_t buf[BLOCK_PROBE_BUF_SIZE];
     int ret = 0;
@@ -549,7 +550,7 @@ static int find_image_format(BlockDriverState *bs, const char *filename,
         return ret;
     }
 
-    ret = bdrv_pread(bs, 0, buf, sizeof(buf));
+    ret = bdrv_pread(file, 0, buf, sizeof(buf));
     if (ret < 0) {
         error_setg_errno(errp, -ret, "Could not read image for determining its "
                          "format");
@@ -1652,7 +1653,7 @@ static BlockDriverState *bdrv_open_inherit(const char *filename,
     /* Image format probing */
     bs->probed = !drv;
     if (!drv && file) {
-        ret = find_image_format(file->bs, filename, &drv, &local_err);
+        ret = find_image_format(file, filename, &drv, &local_err);
         if (ret < 0) {
             goto fail;
         }
diff --git a/block/bochs.c b/block/bochs.c
index 6427ad4fa2..46f635f2e7 100644
--- a/block/bochs.c
+++ b/block/bochs.c
@@ -106,7 +106,7 @@ static int bochs_open(BlockDriverState *bs, QDict *options, int flags,
 
     bs->read_only = true; /* no write support yet */
 
-    ret = bdrv_pread(bs->file->bs, 0, &bochs, sizeof(bochs));
+    ret = bdrv_pread(bs->file, 0, &bochs, sizeof(bochs));
     if (ret < 0) {
         return ret;
     }
@@ -140,7 +140,7 @@ static int bochs_open(BlockDriverState *bs, QDict *options, int flags,
         return -ENOMEM;
     }
 
-    ret = bdrv_pread(bs->file->bs, le32_to_cpu(bochs.header), s->catalog_bitmap,
+    ret = bdrv_pread(bs->file, le32_to_cpu(bochs.header), s->catalog_bitmap,
                      s->catalog_size * 4);
     if (ret < 0) {
         goto fail;
@@ -214,7 +214,7 @@ static int64_t seek_to_sector(BlockDriverState *bs, int64_t sector_num)
         (s->extent_blocks + s->bitmap_blocks));
 
     /* read in bitmap for current extent */
-    ret = bdrv_pread(bs->file->bs, bitmap_offset + (extent_offset / 8),
+    ret = bdrv_pread(bs->file, bitmap_offset + (extent_offset / 8),
                      &bitmap_entry, 1);
     if (ret < 0) {
         return ret;
diff --git a/block/cloop.c b/block/cloop.c
index 8f046e1498..7b75f7ef7b 100644
--- a/block/cloop.c
+++ b/block/cloop.c
@@ -69,7 +69,7 @@ static int cloop_open(BlockDriverState *bs, QDict *options, int flags,
     bs->read_only = true;
 
     /* read header */
-    ret = bdrv_pread(bs->file->bs, 128, &s->block_size, 4);
+    ret = bdrv_pread(bs->file, 128, &s->block_size, 4);
     if (ret < 0) {
         return ret;
     }
@@ -95,7 +95,7 @@ static int cloop_open(BlockDriverState *bs, QDict *options, int flags,
         return -EINVAL;
     }
 
-    ret = bdrv_pread(bs->file->bs, 128 + 4, &s->n_blocks, 4);
+    ret = bdrv_pread(bs->file, 128 + 4, &s->n_blocks, 4);
     if (ret < 0) {
         return ret;
     }
@@ -126,7 +126,7 @@ static int cloop_open(BlockDriverState *bs, QDict *options, int flags,
         return -ENOMEM;
     }
 
-    ret = bdrv_pread(bs->file->bs, 128 + 4 + 4, s->offsets, offsets_size);
+    ret = bdrv_pread(bs->file, 128 + 4 + 4, s->offsets, offsets_size);
     if (ret < 0) {
         goto fail;
     }
@@ -211,7 +211,7 @@ static inline int cloop_read_block(BlockDriverState *bs, int block_num)
         int ret;
         uint32_t bytes = s->offsets[block_num + 1] - s->offsets[block_num];
 
-        ret = bdrv_pread(bs->file->bs, s->offsets[block_num],
+        ret = bdrv_pread(bs->file, s->offsets[block_num],
                          s->compressed_block, bytes);
         if (ret != bytes) {
             return -1;
diff --git a/block/crypto.c b/block/crypto.c
index 64bf095608..cb8cbc2cc9 100644
--- a/block/crypto.c
+++ b/block/crypto.c
@@ -64,7 +64,7 @@ static ssize_t block_crypto_read_func(QCryptoBlock *block,
     BlockDriverState *bs = opaque;
     ssize_t ret;
 
-    ret = bdrv_pread(bs->file->bs, offset, buf, buflen);
+    ret = bdrv_pread(bs->file, offset, buf, buflen);
     if (ret < 0) {
         error_setg_errno(errp, -ret, "Could not read encryption header");
         return ret;
diff --git a/block/dmg.c b/block/dmg.c
index 11a0673f33..b0ed89baa7 100644
--- a/block/dmg.c
+++ b/block/dmg.c
@@ -86,7 +86,7 @@ static int read_uint64(BlockDriverState *bs, int64_t offset, uint64_t *result)
     uint64_t buffer;
     int ret;
 
-    ret = bdrv_pread(bs->file->bs, offset, &buffer, 8);
+    ret = bdrv_pread(bs->file, offset, &buffer, 8);
     if (ret < 0) {
         return ret;
     }
@@ -100,7 +100,7 @@ static int read_uint32(BlockDriverState *bs, int64_t offset, uint32_t *result)
     uint32_t buffer;
     int ret;
 
-    ret = bdrv_pread(bs->file->bs, offset, &buffer, 4);
+    ret = bdrv_pread(bs->file, offset, &buffer, 4);
     if (ret < 0) {
         return ret;
     }
@@ -153,8 +153,9 @@ static void update_max_chunk_size(BDRVDMGState *s, uint32_t chunk,
     }
 }
 
-static int64_t dmg_find_koly_offset(BlockDriverState *file_bs, Error **errp)
+static int64_t dmg_find_koly_offset(BdrvChild *file, Error **errp)
 {
+    BlockDriverState *file_bs = file->bs;
     int64_t length;
     int64_t offset = 0;
     uint8_t buffer[515];
@@ -178,7 +179,7 @@ static int64_t dmg_find_koly_offset(BlockDriverState *file_bs, Error **errp)
         offset = length - 511 - 512;
     }
     length = length < 515 ? length : 515;
-    ret = bdrv_pread(file_bs, offset, buffer, length);
+    ret = bdrv_pread(file, offset, buffer, length);
     if (ret < 0) {
         error_setg_errno(errp, -ret, "Failed while reading UDIF trailer");
         return ret;
@@ -355,7 +356,7 @@ static int dmg_read_resource_fork(BlockDriverState *bs, DmgHeaderState *ds,
         offset += 4;
 
         buffer = g_realloc(buffer, count);
-        ret = bdrv_pread(bs->file->bs, offset, buffer, count);
+        ret = bdrv_pread(bs->file, offset, buffer, count);
         if (ret < 0) {
             goto fail;
         }
@@ -392,7 +393,7 @@ static int dmg_read_plist_xml(BlockDriverState *bs, DmgHeaderState *ds,
 
     buffer = g_malloc(info_length + 1);
     buffer[info_length] = '\0';
-    ret = bdrv_pread(bs->file->bs, info_begin, buffer, info_length);
+    ret = bdrv_pread(bs->file, info_begin, buffer, info_length);
     if (ret != info_length) {
         ret = -EINVAL;
         goto fail;
@@ -448,7 +449,7 @@ static int dmg_open(BlockDriverState *bs, QDict *options, int flags,
     ds.max_sectors_per_chunk = 1;
 
     /* locate the UDIF trailer */
-    offset = dmg_find_koly_offset(bs->file->bs, errp);
+    offset = dmg_find_koly_offset(bs->file, errp);
     if (offset < 0) {
         ret = offset;
         goto fail;
@@ -599,7 +600,7 @@ static inline int dmg_read_chunk(BlockDriverState *bs, uint64_t sector_num)
         case 0x80000005: { /* zlib compressed */
             /* we need to buffer, because only the chunk as whole can be
              * inflated. */
-            ret = bdrv_pread(bs->file->bs, s->offsets[chunk],
+            ret = bdrv_pread(bs->file, s->offsets[chunk],
                              s->compressed_chunk, s->lengths[chunk]);
             if (ret != s->lengths[chunk]) {
                 return -1;
@@ -623,7 +624,7 @@ static inline int dmg_read_chunk(BlockDriverState *bs, uint64_t sector_num)
         case 0x80000006: /* bzip2 compressed */
             /* we need to buffer, because only the chunk as whole can be
              * inflated. */
-            ret = bdrv_pread(bs->file->bs, s->offsets[chunk],
+            ret = bdrv_pread(bs->file, s->offsets[chunk],
                              s->compressed_chunk, s->lengths[chunk]);
             if (ret != s->lengths[chunk]) {
                 return -1;
@@ -648,7 +649,7 @@ static inline int dmg_read_chunk(BlockDriverState *bs, uint64_t sector_num)
             break;
 #endif /* CONFIG_BZIP2 */
         case 1: /* copy */
-            ret = bdrv_pread(bs->file->bs, s->offsets[chunk],
+            ret = bdrv_pread(bs->file, s->offsets[chunk],
                              s->uncompressed_chunk, s->lengths[chunk]);
             if (ret != s->lengths[chunk]) {
                 return -1;
diff --git a/block/io.c b/block/io.c
index 2e04a80010..1240cc5b97 100644
--- a/block/io.c
+++ b/block/io.c
@@ -709,11 +709,11 @@ int bdrv_make_zero(BlockDriverState *bs, BdrvRequestFlags flags)
     }
 }
 
-int bdrv_preadv(BlockDriverState *bs, int64_t offset, QEMUIOVector *qiov)
+int bdrv_preadv(BdrvChild *child, int64_t offset, QEMUIOVector *qiov)
 {
     int ret;
 
-    ret = bdrv_prwv_co(bs, offset, qiov, false, 0);
+    ret = bdrv_prwv_co(child->bs, offset, qiov, false, 0);
     if (ret < 0) {
         return ret;
     }
@@ -721,7 +721,7 @@ int bdrv_preadv(BlockDriverState *bs, int64_t offset, QEMUIOVector *qiov)
     return qiov->size;
 }
 
-int bdrv_pread(BlockDriverState *bs, int64_t offset, void *buf, int bytes)
+int bdrv_pread(BdrvChild *child, int64_t offset, void *buf, int bytes)
 {
     QEMUIOVector qiov;
     struct iovec iov = {
@@ -734,7 +734,7 @@ int bdrv_pread(BlockDriverState *bs, int64_t offset, void *buf, int bytes)
     }
 
     qemu_iovec_init_external(&qiov, &iov, 1);
-    return bdrv_preadv(bs, offset, &qiov);
+    return bdrv_preadv(child, offset, &qiov);
 }
 
 int bdrv_pwritev(BlockDriverState *bs, int64_t offset, QEMUIOVector *qiov)
diff --git a/block/parallels.c b/block/parallels.c
index 91ab61ff2f..85c7cdcd1e 100644
--- a/block/parallels.c
+++ b/block/parallels.c
@@ -576,7 +576,7 @@ static int parallels_open(BlockDriverState *bs, QDict *options, int flags,
     Error *local_err = NULL;
     char *buf;
 
-    ret = bdrv_pread(bs->file->bs, 0, &ph, sizeof(ph));
+    ret = bdrv_pread(bs->file, 0, &ph, sizeof(ph));
     if (ret < 0) {
         goto fail;
     }
@@ -631,7 +631,7 @@ static int parallels_open(BlockDriverState *bs, QDict *options, int flags,
         s->header_size = size;
     }
 
-    ret = bdrv_pread(bs->file->bs, 0, s->header, s->header_size);
+    ret = bdrv_pread(bs->file, 0, s->header, s->header_size);
     if (ret < 0) {
         goto fail;
     }
diff --git a/block/qcow.c b/block/qcow.c
index 674595ea54..55ffccbefd 100644
--- a/block/qcow.c
+++ b/block/qcow.c
@@ -105,7 +105,7 @@ static int qcow_open(BlockDriverState *bs, QDict *options, int flags,
     int ret;
     QCowHeader header;
 
-    ret = bdrv_pread(bs->file->bs, 0, &header, sizeof(header));
+    ret = bdrv_pread(bs->file, 0, &header, sizeof(header));
     if (ret < 0) {
         goto fail;
     }
@@ -208,7 +208,7 @@ static int qcow_open(BlockDriverState *bs, QDict *options, int flags,
         goto fail;
     }
 
-    ret = bdrv_pread(bs->file->bs, s->l1_table_offset, s->l1_table,
+    ret = bdrv_pread(bs->file, s->l1_table_offset, s->l1_table,
                s->l1_size * sizeof(uint64_t));
     if (ret < 0) {
         goto fail;
@@ -239,7 +239,7 @@ static int qcow_open(BlockDriverState *bs, QDict *options, int flags,
             ret = -EINVAL;
             goto fail;
         }
-        ret = bdrv_pread(bs->file->bs, header.backing_file_offset,
+        ret = bdrv_pread(bs->file, header.backing_file_offset,
                    bs->backing_file, len);
         if (ret < 0) {
             goto fail;
@@ -424,7 +424,7 @@ static uint64_t get_cluster_offset(BlockDriverState *bs,
                 s->l2_size * sizeof(uint64_t)) < 0)
             return 0;
     } else {
-        if (bdrv_pread(bs->file->bs, l2_offset, l2_table,
+        if (bdrv_pread(bs->file, l2_offset, l2_table,
                        s->l2_size * sizeof(uint64_t)) !=
             s->l2_size * sizeof(uint64_t))
             return 0;
@@ -565,7 +565,7 @@ static int decompress_cluster(BlockDriverState *bs, uint64_t cluster_offset)
     if (s->cluster_cache_offset != coffset) {
         csize = cluster_offset >> (63 - s->cluster_bits);
         csize &= (s->cluster_size - 1);
-        ret = bdrv_pread(bs->file->bs, coffset, s->cluster_data, csize);
+        ret = bdrv_pread(bs->file, coffset, s->cluster_data, csize);
         if (ret != csize)
             return -1;
         if (decompress_buffer(s->cluster_cache, s->cluster_size,
diff --git a/block/qcow2-cache.c b/block/qcow2-cache.c
index 580631c3d8..5eba75f42e 100644
--- a/block/qcow2-cache.c
+++ b/block/qcow2-cache.c
@@ -357,7 +357,7 @@ static int qcow2_cache_do_get(BlockDriverState *bs, Qcow2Cache *c,
             BLKDBG_EVENT(bs->file, BLKDBG_L2_LOAD);
         }
 
-        ret = bdrv_pread(bs->file->bs, offset,
+        ret = bdrv_pread(bs->file, offset,
                          qcow2_cache_get_table_addr(bs, c, i),
                          s->cluster_size);
         if (ret < 0) {
diff --git a/block/qcow2-refcount.c b/block/qcow2-refcount.c
index 12e7e6b9a2..e5419746af 100644
--- a/block/qcow2-refcount.c
+++ b/block/qcow2-refcount.c
@@ -104,7 +104,7 @@ int qcow2_refcount_init(BlockDriverState *bs)
             goto fail;
         }
         BLKDBG_EVENT(bs->file, BLKDBG_REFTABLE_LOAD);
-        ret = bdrv_pread(bs->file->bs, s->refcount_table_offset,
+        ret = bdrv_pread(bs->file, s->refcount_table_offset,
                          s->refcount_table, refcount_table_size2);
         if (ret < 0) {
             goto fail;
@@ -1070,7 +1070,7 @@ int qcow2_update_snapshot_refcount(BlockDriverState *bs,
         }
         l1_allocated = true;
 
-        ret = bdrv_pread(bs->file->bs, l1_table_offset, l1_table, l1_size2);
+        ret = bdrv_pread(bs->file, l1_table_offset, l1_table, l1_size2);
         if (ret < 0) {
             goto fail;
         }
@@ -1382,7 +1382,7 @@ static int check_refcounts_l2(BlockDriverState *bs, BdrvCheckResult *res,
     l2_size = s->l2_size * sizeof(uint64_t);
     l2_table = g_malloc(l2_size);
 
-    ret = bdrv_pread(bs->file->bs, l2_offset, l2_table, l2_size);
+    ret = bdrv_pread(bs->file, l2_offset, l2_table, l2_size);
     if (ret < 0) {
         fprintf(stderr, "ERROR: I/O error in check_refcounts_l2\n");
         res->check_errors++;
@@ -1514,7 +1514,7 @@ static int check_refcounts_l1(BlockDriverState *bs,
             res->check_errors++;
             goto fail;
         }
-        ret = bdrv_pread(bs->file->bs, l1_table_offset, l1_table, l1_size2);
+        ret = bdrv_pread(bs->file, l1_table_offset, l1_table, l1_size2);
         if (ret < 0) {
             fprintf(stderr, "ERROR: I/O error in check_refcounts_l1\n");
             res->check_errors++;
@@ -1612,7 +1612,7 @@ static int check_oflag_copied(BlockDriverState *bs, BdrvCheckResult *res,
             }
         }
 
-        ret = bdrv_pread(bs->file->bs, l2_offset, l2_table,
+        ret = bdrv_pread(bs->file, l2_offset, l2_table,
                          s->l2_size * sizeof(uint64_t));
         if (ret < 0) {
             fprintf(stderr, "ERROR: Could not read L2 table: %s\n",
@@ -2407,7 +2407,7 @@ int qcow2_check_metadata_overlap(BlockDriverState *bs, int ign, int64_t offset,
                 return -ENOMEM;
             }
 
-            ret = bdrv_pread(bs->file->bs, l1_ofs, l1, l1_sz2);
+            ret = bdrv_pread(bs->file, l1_ofs, l1, l1_sz2);
             if (ret < 0) {
                 g_free(l1);
                 return ret;
diff --git a/block/qcow2-snapshot.c b/block/qcow2-snapshot.c
index 242fb21d6e..2693ebf812 100644
--- a/block/qcow2-snapshot.c
+++ b/block/qcow2-snapshot.c
@@ -67,7 +67,7 @@ int qcow2_read_snapshots(BlockDriverState *bs)
     for(i = 0; i < s->nb_snapshots; i++) {
         /* Read statically sized part of the snapshot header */
         offset = align_offset(offset, 8);
-        ret = bdrv_pread(bs->file->bs, offset, &h, sizeof(h));
+        ret = bdrv_pread(bs->file, offset, &h, sizeof(h));
         if (ret < 0) {
             goto fail;
         }
@@ -86,7 +86,7 @@ int qcow2_read_snapshots(BlockDriverState *bs)
         name_size = be16_to_cpu(h.name_size);
 
         /* Read extra data */
-        ret = bdrv_pread(bs->file->bs, offset, &extra,
+        ret = bdrv_pread(bs->file, offset, &extra,
                          MIN(sizeof(extra), extra_data_size));
         if (ret < 0) {
             goto fail;
@@ -105,7 +105,7 @@ int qcow2_read_snapshots(BlockDriverState *bs)
 
         /* Read snapshot ID */
         sn->id_str = g_malloc(id_str_size + 1);
-        ret = bdrv_pread(bs->file->bs, offset, sn->id_str, id_str_size);
+        ret = bdrv_pread(bs->file, offset, sn->id_str, id_str_size);
         if (ret < 0) {
             goto fail;
         }
@@ -114,7 +114,7 @@ int qcow2_read_snapshots(BlockDriverState *bs)
 
         /* Read snapshot name */
         sn->name = g_malloc(name_size + 1);
-        ret = bdrv_pread(bs->file->bs, offset, sn->name, name_size);
+        ret = bdrv_pread(bs->file, offset, sn->name, name_size);
         if (ret < 0) {
             goto fail;
         }
@@ -512,7 +512,7 @@ int qcow2_snapshot_goto(BlockDriverState *bs, const char *snapshot_id)
         goto fail;
     }
 
-    ret = bdrv_pread(bs->file->bs, sn->l1_table_offset,
+    ret = bdrv_pread(bs->file, sn->l1_table_offset,
                      sn_l1_table, sn_l1_bytes);
     if (ret < 0) {
         goto fail;
@@ -716,7 +716,7 @@ int qcow2_snapshot_load_tmp(BlockDriverState *bs,
         return -ENOMEM;
     }
 
-    ret = bdrv_pread(bs->file->bs, sn->l1_table_offset,
+    ret = bdrv_pread(bs->file, sn->l1_table_offset,
                      new_l1_table, new_l1_bytes);
     if (ret < 0) {
         error_setg(errp, "Failed to read l1 table for snapshot");
diff --git a/block/qcow2.c b/block/qcow2.c
index cd9c27b085..b7313d22b5 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -107,7 +107,7 @@ static int qcow2_read_extensions(BlockDriverState *bs, uint64_t start_offset,
         printf("attempting to read extended header in offset %lu\n", offset);
 #endif
 
-        ret = bdrv_pread(bs->file->bs, offset, &ext, sizeof(ext));
+        ret = bdrv_pread(bs->file, offset, &ext, sizeof(ext));
         if (ret < 0) {
             error_setg_errno(errp, -ret, "qcow2_read_extension: ERROR: "
                              "pread fail from offset %" PRIu64, offset);
@@ -135,7 +135,7 @@ static int qcow2_read_extensions(BlockDriverState *bs, uint64_t start_offset,
                            sizeof(bs->backing_format));
                 return 2;
             }
-            ret = bdrv_pread(bs->file->bs, offset, bs->backing_format, ext.len);
+            ret = bdrv_pread(bs->file, offset, bs->backing_format, ext.len);
             if (ret < 0) {
                 error_setg_errno(errp, -ret, "ERROR: ext_backing_format: "
                                  "Could not read format name");
@@ -151,7 +151,7 @@ static int qcow2_read_extensions(BlockDriverState *bs, uint64_t start_offset,
         case QCOW2_EXT_MAGIC_FEATURE_TABLE:
             if (p_feature_table != NULL) {
                 void* feature_table = g_malloc0(ext.len + 2 * sizeof(Qcow2Feature));
-                ret = bdrv_pread(bs->file->bs, offset , feature_table, ext.len);
+                ret = bdrv_pread(bs->file, offset , feature_table, ext.len);
                 if (ret < 0) {
                     error_setg_errno(errp, -ret, "ERROR: ext_feature_table: "
                                      "Could not read table");
@@ -172,7 +172,7 @@ static int qcow2_read_extensions(BlockDriverState *bs, uint64_t start_offset,
                 uext->len = ext.len;
                 QLIST_INSERT_HEAD(&s->unknown_header_ext, uext, next);
 
-                ret = bdrv_pread(bs->file->bs, offset , uext->data, uext->len);
+                ret = bdrv_pread(bs->file, offset , uext->data, uext->len);
                 if (ret < 0) {
                     error_setg_errno(errp, -ret, "ERROR: unknown extension: "
                                      "Could not read data");
@@ -817,7 +817,7 @@ static int qcow2_open(BlockDriverState *bs, QDict *options, int flags,
     uint64_t ext_end;
     uint64_t l1_vm_state_index;
 
-    ret = bdrv_pread(bs->file->bs, 0, &header, sizeof(header));
+    ret = bdrv_pread(bs->file, 0, &header, sizeof(header));
     if (ret < 0) {
         error_setg_errno(errp, -ret, "Could not read qcow2 header");
         goto fail;
@@ -892,7 +892,7 @@ static int qcow2_open(BlockDriverState *bs, QDict *options, int flags,
     if (header.header_length > sizeof(header)) {
         s->unknown_header_fields_size = header.header_length - sizeof(header);
         s->unknown_header_fields = g_malloc(s->unknown_header_fields_size);
-        ret = bdrv_pread(bs->file->bs, sizeof(header), s->unknown_header_fields,
+        ret = bdrv_pread(bs->file, sizeof(header), s->unknown_header_fields,
                          s->unknown_header_fields_size);
         if (ret < 0) {
             error_setg_errno(errp, -ret, "Could not read unknown qcow2 header "
@@ -1066,7 +1066,7 @@ static int qcow2_open(BlockDriverState *bs, QDict *options, int flags,
             ret = -ENOMEM;
             goto fail;
         }
-        ret = bdrv_pread(bs->file->bs, s->l1_table_offset, s->l1_table,
+        ret = bdrv_pread(bs->file, s->l1_table_offset, s->l1_table,
                          s->l1_size * sizeof(uint64_t));
         if (ret < 0) {
             error_setg_errno(errp, -ret, "Could not read L1 table");
@@ -1122,7 +1122,7 @@ static int qcow2_open(BlockDriverState *bs, QDict *options, int flags,
             ret = -EINVAL;
             goto fail;
         }
-        ret = bdrv_pread(bs->file->bs, header.backing_file_offset,
+        ret = bdrv_pread(bs->file, header.backing_file_offset,
                          bs->backing_file, len);
         if (ret < 0) {
             error_setg_errno(errp, -ret, "Could not read backing file name");
diff --git a/block/qed.c b/block/qed.c
index 9d3d588631..d6d5e33459 100644
--- a/block/qed.c
+++ b/block/qed.c
@@ -218,7 +218,7 @@ static bool qed_is_image_size_valid(uint64_t image_size, uint32_t cluster_size,
  *
  * The string is NUL-terminated.
  */
-static int qed_read_string(BlockDriverState *file, uint64_t offset, size_t n,
+static int qed_read_string(BdrvChild *file, uint64_t offset, size_t n,
                            char *buf, size_t buflen)
 {
     int ret;
@@ -389,7 +389,7 @@ static int bdrv_qed_open(BlockDriverState *bs, QDict *options, int flags,
     s->bs = bs;
     QSIMPLEQ_INIT(&s->allocating_write_reqs);
 
-    ret = bdrv_pread(bs->file->bs, 0, &le_header, sizeof(le_header));
+    ret = bdrv_pread(bs->file, 0, &le_header, sizeof(le_header));
     if (ret < 0) {
         return ret;
     }
@@ -446,7 +446,7 @@ static int bdrv_qed_open(BlockDriverState *bs, QDict *options, int flags,
             return -EINVAL;
         }
 
-        ret = qed_read_string(bs->file->bs, s->header.backing_filename_offset,
+        ret = qed_read_string(bs->file, s->header.backing_filename_offset,
                               s->header.backing_filename_size, bs->backing_file,
                               sizeof(bs->backing_file));
         if (ret < 0) {
diff --git a/block/vhdx-log.c b/block/vhdx-log.c
index 8ab7d22d9a..1e3928f8bb 100644
--- a/block/vhdx-log.c
+++ b/block/vhdx-log.c
@@ -84,7 +84,7 @@ static int vhdx_log_peek_hdr(BlockDriverState *bs, VHDXLogEntries *log,
 
     offset = log->offset + read;
 
-    ret = bdrv_pread(bs->file->bs, offset, hdr, sizeof(VHDXLogEntryHeader));
+    ret = bdrv_pread(bs->file, offset, hdr, sizeof(VHDXLogEntryHeader));
     if (ret < 0) {
         goto exit;
     }
@@ -144,7 +144,7 @@ static int vhdx_log_read_sectors(BlockDriverState *bs, VHDXLogEntries *log,
         }
         offset = log->offset + read;
 
-        ret = bdrv_pread(bs->file->bs, offset, buffer, VHDX_LOG_SECTOR_SIZE);
+        ret = bdrv_pread(bs->file, offset, buffer, VHDX_LOG_SECTOR_SIZE);
         if (ret < 0) {
             goto exit;
         }
@@ -945,7 +945,7 @@ static int vhdx_log_write(BlockDriverState *bs, BDRVVHDXState *s,
 
         if (i == 0 && leading_length) {
             /* partial sector at the front of the buffer */
-            ret = bdrv_pread(bs->file->bs, file_offset, merged_sector,
+            ret = bdrv_pread(bs->file, file_offset, merged_sector,
                              VHDX_LOG_SECTOR_SIZE);
             if (ret < 0) {
                 goto exit;
@@ -955,7 +955,7 @@ static int vhdx_log_write(BlockDriverState *bs, BDRVVHDXState *s,
             sector_write = merged_sector;
         } else if (i == sectors - 1 && trailing_length) {
             /* partial sector at the end of the buffer */
-            ret = bdrv_pread(bs->file->bs,
+            ret = bdrv_pread(bs->file,
                             file_offset,
                             merged_sector + trailing_length,
                             VHDX_LOG_SECTOR_SIZE - trailing_length);
diff --git a/block/vhdx.c b/block/vhdx.c
index b0f66deb9d..c5ec6087a2 100644
--- a/block/vhdx.c
+++ b/block/vhdx.c
@@ -298,9 +298,10 @@ static int vhdx_probe(const uint8_t *buf, int buf_size, const char *filename)
  * and then update the header checksum.  Header is converted to proper
  * endianness before being written to the specified file offset
  */
-static int vhdx_write_header(BlockDriverState *bs_file, VHDXHeader *hdr,
+static int vhdx_write_header(BdrvChild *file, VHDXHeader *hdr,
                              uint64_t offset, bool read)
 {
+    BlockDriverState *bs_file = file->bs;
     uint8_t *buffer = NULL;
     int ret;
     VHDXHeader *header_le;
@@ -315,7 +316,7 @@ static int vhdx_write_header(BlockDriverState *bs_file, VHDXHeader *hdr,
     buffer = qemu_blockalign(bs_file, VHDX_HEADER_SIZE);
     if (read) {
         /* if true, we can't assume the extra reserved bytes are 0 */
-        ret = bdrv_pread(bs_file, offset, buffer, VHDX_HEADER_SIZE);
+        ret = bdrv_pread(file, offset, buffer, VHDX_HEADER_SIZE);
         if (ret < 0) {
             goto exit;
         }
@@ -378,7 +379,7 @@ static int vhdx_update_header(BlockDriverState *bs, BDRVVHDXState *s,
         inactive_header->log_guid = *log_guid;
     }
 
-    ret = vhdx_write_header(bs->file->bs, inactive_header, header_offset, true);
+    ret = vhdx_write_header(bs->file, inactive_header, header_offset, true);
     if (ret < 0) {
         goto exit;
     }
@@ -430,7 +431,7 @@ static void vhdx_parse_header(BlockDriverState *bs, BDRVVHDXState *s,
     /* We have to read the whole VHDX_HEADER_SIZE instead of
      * sizeof(VHDXHeader), because the checksum is over the whole
      * region */
-    ret = bdrv_pread(bs->file->bs, VHDX_HEADER1_OFFSET, buffer,
+    ret = bdrv_pread(bs->file, VHDX_HEADER1_OFFSET, buffer,
                      VHDX_HEADER_SIZE);
     if (ret < 0) {
         goto fail;
@@ -447,7 +448,7 @@ static void vhdx_parse_header(BlockDriverState *bs, BDRVVHDXState *s,
         }
     }
 
-    ret = bdrv_pread(bs->file->bs, VHDX_HEADER2_OFFSET, buffer,
+    ret = bdrv_pread(bs->file, VHDX_HEADER2_OFFSET, buffer,
                      VHDX_HEADER_SIZE);
     if (ret < 0) {
         goto fail;
@@ -521,7 +522,7 @@ static int vhdx_open_region_tables(BlockDriverState *bs, BDRVVHDXState *s)
      * whole block */
     buffer = qemu_blockalign(bs, VHDX_HEADER_BLOCK_SIZE);
 
-    ret = bdrv_pread(bs->file->bs, VHDX_REGION_TABLE_OFFSET, buffer,
+    ret = bdrv_pread(bs->file, VHDX_REGION_TABLE_OFFSET, buffer,
                      VHDX_HEADER_BLOCK_SIZE);
     if (ret < 0) {
         goto fail;
@@ -634,7 +635,7 @@ static int vhdx_parse_metadata(BlockDriverState *bs, BDRVVHDXState *s)
 
     buffer = qemu_blockalign(bs, VHDX_METADATA_TABLE_MAX_SIZE);
 
-    ret = bdrv_pread(bs->file->bs, s->metadata_rt.file_offset, buffer,
+    ret = bdrv_pread(bs->file, s->metadata_rt.file_offset, buffer,
                      VHDX_METADATA_TABLE_MAX_SIZE);
     if (ret < 0) {
         goto exit;
@@ -737,7 +738,7 @@ static int vhdx_parse_metadata(BlockDriverState *bs, BDRVVHDXState *s)
         goto exit;
     }
 
-    ret = bdrv_pread(bs->file->bs,
+    ret = bdrv_pread(bs->file,
                      s->metadata_entries.file_parameters_entry.offset
                                          + s->metadata_rt.file_offset,
                      &s->params,
@@ -772,7 +773,7 @@ static int vhdx_parse_metadata(BlockDriverState *bs, BDRVVHDXState *s)
     /* determine virtual disk size, logical sector size,
      * and phys sector size */
 
-    ret = bdrv_pread(bs->file->bs,
+    ret = bdrv_pread(bs->file,
                      s->metadata_entries.virtual_disk_size_entry.offset
                                            + s->metadata_rt.file_offset,
                      &s->virtual_disk_size,
@@ -780,7 +781,7 @@ static int vhdx_parse_metadata(BlockDriverState *bs, BDRVVHDXState *s)
     if (ret < 0) {
         goto exit;
     }
-    ret = bdrv_pread(bs->file->bs,
+    ret = bdrv_pread(bs->file,
                      s->metadata_entries.logical_sector_size_entry.offset
                                              + s->metadata_rt.file_offset,
                      &s->logical_sector_size,
@@ -788,7 +789,7 @@ static int vhdx_parse_metadata(BlockDriverState *bs, BDRVVHDXState *s)
     if (ret < 0) {
         goto exit;
     }
-    ret = bdrv_pread(bs->file->bs,
+    ret = bdrv_pread(bs->file,
                      s->metadata_entries.phys_sector_size_entry.offset
                                           + s->metadata_rt.file_offset,
                      &s->physical_sector_size,
@@ -905,7 +906,7 @@ static int vhdx_open(BlockDriverState *bs, QDict *options, int flags,
     QLIST_INIT(&s->regions);
 
     /* validate the file signature */
-    ret = bdrv_pread(bs->file->bs, 0, &signature, sizeof(uint64_t));
+    ret = bdrv_pread(bs->file, 0, &signature, sizeof(uint64_t));
     if (ret < 0) {
         goto fail;
     }
@@ -964,7 +965,7 @@ static int vhdx_open(BlockDriverState *bs, QDict *options, int flags,
         goto fail;
     }
 
-    ret = bdrv_pread(bs->file->bs, s->bat_offset, s->bat, s->bat_rt.length);
+    ret = bdrv_pread(bs->file, s->bat_offset, s->bat, s->bat_rt.length);
     if (ret < 0) {
         goto fail;
     }
@@ -1391,6 +1392,7 @@ static int vhdx_create_new_headers(BlockBackend *blk, uint64_t image_size,
                                    uint32_t log_size)
 {
     BlockDriverState *bs = blk_bs(blk);
+    BdrvChild *child;
     int ret = 0;
     VHDXHeader *hdr = NULL;
 
@@ -1405,12 +1407,18 @@ static int vhdx_create_new_headers(BlockBackend *blk, uint64_t image_size,
     vhdx_guid_generate(&hdr->file_write_guid);
     vhdx_guid_generate(&hdr->data_write_guid);
 
-    ret = vhdx_write_header(bs, hdr, VHDX_HEADER1_OFFSET, false);
+    /* XXX Ugly way to get blk->root, but that's a feature, not a bug. This
+     * hack makes it obvious that vhdx_write_header() bypasses the BlockBackend
+     * here, which it really shouldn't be doing. */
+    child = QLIST_FIRST(&bs->parents);
+    assert(!QLIST_NEXT(child, next_parent));
+
+    ret = vhdx_write_header(child, hdr, VHDX_HEADER1_OFFSET, false);
     if (ret < 0) {
         goto exit;
     }
     hdr->sequence_number++;
-    ret = vhdx_write_header(bs, hdr, VHDX_HEADER2_OFFSET, false);
+    ret = vhdx_write_header(child, hdr, VHDX_HEADER2_OFFSET, false);
     if (ret < 0) {
         goto exit;
     }
diff --git a/block/vmdk.c b/block/vmdk.c
index 2901692700..a2c85a206d 100644
--- a/block/vmdk.c
+++ b/block/vmdk.c
@@ -252,7 +252,7 @@ static uint32_t vmdk_read_cid(BlockDriverState *bs, int parent)
     int ret;
 
     desc = g_malloc0(DESC_SIZE);
-    ret = bdrv_pread(bs->file->bs, s->desc_offset, desc, DESC_SIZE);
+    ret = bdrv_pread(bs->file, s->desc_offset, desc, DESC_SIZE);
     if (ret < 0) {
         g_free(desc);
         return 0;
@@ -286,7 +286,7 @@ static int vmdk_write_cid(BlockDriverState *bs, uint32_t cid)
 
     desc = g_malloc0(DESC_SIZE);
     tmp_desc = g_malloc0(DESC_SIZE);
-    ret = bdrv_pread(bs->file->bs, s->desc_offset, desc, DESC_SIZE);
+    ret = bdrv_pread(bs->file, s->desc_offset, desc, DESC_SIZE);
     if (ret < 0) {
         goto out;
     }
@@ -350,7 +350,7 @@ static int vmdk_parent_open(BlockDriverState *bs)
     int ret;
 
     desc = g_malloc0(DESC_SIZE + 1);
-    ret = bdrv_pread(bs->file->bs, s->desc_offset, desc, DESC_SIZE);
+    ret = bdrv_pread(bs->file, s->desc_offset, desc, DESC_SIZE);
     if (ret < 0) {
         goto out;
     }
@@ -454,7 +454,7 @@ static int vmdk_init_tables(BlockDriverState *bs, VmdkExtent *extent,
         return -ENOMEM;
     }
 
-    ret = bdrv_pread(extent->file->bs,
+    ret = bdrv_pread(extent->file,
                      extent->l1_table_offset,
                      extent->l1_table,
                      l1_size);
@@ -474,7 +474,7 @@ static int vmdk_init_tables(BlockDriverState *bs, VmdkExtent *extent,
             ret = -ENOMEM;
             goto fail_l1;
         }
-        ret = bdrv_pread(extent->file->bs,
+        ret = bdrv_pread(extent->file,
                          extent->l1_backup_table_offset,
                          extent->l1_backup_table,
                          l1_size);
@@ -508,7 +508,7 @@ static int vmdk_open_vmfs_sparse(BlockDriverState *bs,
     VMDK3Header header;
     VmdkExtent *extent;
 
-    ret = bdrv_pread(file->bs, sizeof(magic), &header, sizeof(header));
+    ret = bdrv_pread(file, sizeof(magic), &header, sizeof(header));
     if (ret < 0) {
         error_setg_errno(errp, -ret,
                          "Could not read header from file '%s'",
@@ -538,14 +538,13 @@ static int vmdk_open_vmfs_sparse(BlockDriverState *bs,
 static int vmdk_open_desc_file(BlockDriverState *bs, int flags, char *buf,
                                QDict *options, Error **errp);
 
-static char *vmdk_read_desc(BlockDriverState *file, uint64_t desc_offset,
-                            Error **errp)
+static char *vmdk_read_desc(BdrvChild *file, uint64_t desc_offset, Error **errp)
 {
     int64_t size;
     char *buf;
     int ret;
 
-    size = bdrv_getlength(file);
+    size = bdrv_getlength(file->bs);
     if (size < 0) {
         error_setg_errno(errp, -size, "Could not access file");
         return NULL;
@@ -586,7 +585,7 @@ static int vmdk_open_vmdk4(BlockDriverState *bs,
     int64_t l1_backup_offset = 0;
     bool compressed;
 
-    ret = bdrv_pread(file->bs, sizeof(magic), &header, sizeof(header));
+    ret = bdrv_pread(file, sizeof(magic), &header, sizeof(header));
     if (ret < 0) {
         error_setg_errno(errp, -ret,
                          "Could not read header from file '%s'",
@@ -596,7 +595,7 @@ static int vmdk_open_vmdk4(BlockDriverState *bs,
     if (header.capacity == 0) {
         uint64_t desc_offset = le64_to_cpu(header.desc_offset);
         if (desc_offset) {
-            char *buf = vmdk_read_desc(file->bs, desc_offset << 9, errp);
+            char *buf = vmdk_read_desc(file, desc_offset << 9, errp);
             if (!buf) {
                 return -EINVAL;
             }
@@ -636,7 +635,7 @@ static int vmdk_open_vmdk4(BlockDriverState *bs,
             } QEMU_PACKED eos_marker;
         } QEMU_PACKED footer;
 
-        ret = bdrv_pread(file->bs,
+        ret = bdrv_pread(file,
             bs->file->bs->total_sectors * 512 - 1536,
             &footer, sizeof(footer));
         if (ret < 0) {
@@ -874,7 +873,7 @@ static int vmdk_parse_extents(const char *desc, BlockDriverState *bs,
             extent->flat_start_offset = flat_offset << 9;
         } else if (!strcmp(type, "SPARSE") || !strcmp(type, "VMFSSPARSE")) {
             /* SPARSE extent and VMFSSPARSE extent are both "COWD" sparse file*/
-            char *buf = vmdk_read_desc(extent_file->bs, 0, errp);
+            char *buf = vmdk_read_desc(extent_file, 0, errp);
             if (!buf) {
                 ret = -EINVAL;
             } else {
@@ -943,7 +942,7 @@ static int vmdk_open(BlockDriverState *bs, QDict *options, int flags,
     BDRVVmdkState *s = bs->opaque;
     uint32_t magic;
 
-    buf = vmdk_read_desc(bs->file->bs, 0, errp);
+    buf = vmdk_read_desc(bs->file, 0, errp);
     if (!buf) {
         return -EINVAL;
     }
@@ -1046,7 +1045,7 @@ static int get_whole_cluster(BlockDriverState *bs,
     /* Read backing data before skip range */
     if (skip_start_bytes > 0) {
         if (bs->backing) {
-            ret = bdrv_pread(bs->backing->bs, offset, whole_grain,
+            ret = bdrv_pread(bs->backing, offset, whole_grain,
                              skip_start_bytes);
             if (ret < 0) {
                 ret = VMDK_ERROR;
@@ -1063,7 +1062,7 @@ static int get_whole_cluster(BlockDriverState *bs,
     /* Read backing data after skip range */
     if (skip_end_bytes < cluster_bytes) {
         if (bs->backing) {
-            ret = bdrv_pread(bs->backing->bs, offset + skip_end_bytes,
+            ret = bdrv_pread(bs->backing, offset + skip_end_bytes,
                              whole_grain + skip_end_bytes,
                              cluster_bytes - skip_end_bytes);
             if (ret < 0) {
@@ -1191,8 +1190,7 @@ static int get_cluster_offset(BlockDriverState *bs,
         }
     }
     l2_table = extent->l2_cache + (min_index * extent->l2_size);
-    if (bdrv_pread(
-                extent->file->bs,
+    if (bdrv_pread(extent->file,
                 (int64_t)l2_offset * 512,
                 l2_table,
                 extent->l2_size * sizeof(uint32_t)
@@ -1424,7 +1422,7 @@ static int vmdk_read_extent(VmdkExtent *extent, int64_t cluster_offset,
     buf_bytes = cluster_bytes * 2;
     cluster_buf = g_malloc(buf_bytes);
     uncomp_buf = g_malloc(cluster_bytes);
-    ret = bdrv_pread(extent->file->bs,
+    ret = bdrv_pread(extent->file,
                 cluster_offset,
                 cluster_buf, buf_bytes);
     if (ret < 0) {
diff --git a/block/vpc.c b/block/vpc.c
index 076a7ce399..9528637fca 100644
--- a/block/vpc.c
+++ b/block/vpc.c
@@ -237,7 +237,7 @@ static int vpc_open(BlockDriverState *bs, QDict *options, int flags,
         goto fail;
     }
 
-    ret = bdrv_pread(bs->file->bs, 0, s->footer_buf, HEADER_SIZE);
+    ret = bdrv_pread(bs->file, 0, s->footer_buf, HEADER_SIZE);
     if (ret < 0) {
         error_setg(errp, "Unable to read VHD header");
         goto fail;
@@ -257,7 +257,7 @@ static int vpc_open(BlockDriverState *bs, QDict *options, int flags,
         }
 
         /* If a fixed disk, the footer is found only at the end of the file */
-        ret = bdrv_pread(bs->file->bs, offset-HEADER_SIZE, s->footer_buf,
+        ret = bdrv_pread(bs->file, offset-HEADER_SIZE, s->footer_buf,
                          HEADER_SIZE);
         if (ret < 0) {
             goto fail;
@@ -328,7 +328,7 @@ static int vpc_open(BlockDriverState *bs, QDict *options, int flags,
     }
 
     if (disk_type == VHD_DYNAMIC) {
-        ret = bdrv_pread(bs->file->bs, be64_to_cpu(footer->data_offset), buf,
+        ret = bdrv_pread(bs->file, be64_to_cpu(footer->data_offset), buf,
                          HEADER_SIZE);
         if (ret < 0) {
             error_setg(errp, "Error reading dynamic VHD header");
@@ -385,7 +385,7 @@ static int vpc_open(BlockDriverState *bs, QDict *options, int flags,
 
         s->bat_offset = be64_to_cpu(dyndisk_header->table_offset);
 
-        ret = bdrv_pread(bs->file->bs, s->bat_offset, s->pagetable,
+        ret = bdrv_pread(bs->file, s->bat_offset, s->pagetable,
                          pagetable_size);
         if (ret < 0) {
             error_setg(errp, "Error reading pagetable");
diff --git a/include/block/block.h b/include/block/block.h
index ea17936f41..4b1d090378 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -233,9 +233,8 @@ int bdrv_write(BdrvChild *child, int64_t sector_num,
 int bdrv_pwrite_zeroes(BlockDriverState *bs, int64_t offset,
                        int count, BdrvRequestFlags flags);
 int bdrv_make_zero(BlockDriverState *bs, BdrvRequestFlags flags);
-int bdrv_pread(BlockDriverState *bs, int64_t offset,
-               void *buf, int count);
-int bdrv_preadv(BlockDriverState *bs, int64_t offset, QEMUIOVector *qiov);
+int bdrv_pread(BdrvChild *child, int64_t offset, void *buf, int bytes);
+int bdrv_preadv(BdrvChild *child, int64_t offset, QEMUIOVector *qiov);
 int bdrv_pwrite(BlockDriverState *bs, int64_t offset,
                 const void *buf, int count);
 int bdrv_pwritev(BlockDriverState *bs, int64_t offset, QEMUIOVector *qiov);