Merge remote-tracking branch 'remotes/stefanha/tags/block-pull-request' into staging

Pull request

# gpg: Signature made Tue 27 Aug 2019 21:16:27 BST
# gpg:                using RSA key 8695A8BFD3F97CDAAC35775A9CA4ABB381AB73C8
# gpg: Good signature from "Stefan Hajnoczi <stefanha@redhat.com>" [full]
# gpg:                 aka "Stefan Hajnoczi <stefanha@gmail.com>" [full]
# Primary key fingerprint: 8695 A8BF D3F9 7CDA AC35  775A 9CA4 ABB3 81AB 73C8

* remotes/stefanha/tags/block-pull-request:
  block/qcow2: implement .bdrv_co_pwritev(_compressed)_part
  block/qcow2: implement .bdrv_co_preadv_part
  block/qcow2: refactor qcow2_co_preadv to use buffer-based io
  block/io: introduce bdrv_co_p{read, write}v_part
  block/io: bdrv_aligned_pwritev: use and support qiov_offset
  block/io: bdrv_aligned_preadv: use and support qiov_offset
  block/io: bdrv_co_do_copy_on_readv: lazy allocation
  block/io: bdrv_co_do_copy_on_readv: use and support qiov_offset
  block: define .*_part io handlers in BlockDriver
  block/io: refactor padding
  util/iov: improve qemu_iovec_is_zero
  util/iov: introduce qemu_iovec_init_extended

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

block/backup.c

@@ -674,7 +674,7 @@ BlockJob *backup_job_create(const char *job_id, BlockDriverState *bs,
         return NULL;
     }
 
-    if (compress && target->drv->bdrv_co_pwritev_compressed == NULL) {
+    if (compress && !block_driver_can_compress(target->drv)) {
         error_setg(errp, "Compression is not supported for this drive %s",
                    bdrv_get_device_name(target));
         return NULL;

block/qcow2-cluster.c

@@ -452,8 +452,9 @@ static int coroutine_fn do_perform_cow_read(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_preadv(bs, src_cluster_offset + offset_in_cluster,
-                                  qiov->size, qiov, 0);
+    ret = bs->drv->bdrv_co_preadv_part(bs,
+                                       src_cluster_offset + offset_in_cluster,
+                                       qiov->size, qiov, 0, 0);
     if (ret < 0) {
         return ret;
     }
@@ -828,7 +829,6 @@ static int perform_cow(BlockDriverState *bs, QCowL2Meta *m)
     assert(start->nb_bytes <= UINT_MAX - end->nb_bytes);
     assert(start->nb_bytes + end->nb_bytes <= UINT_MAX - data_bytes);
     assert(start->offset + start->nb_bytes <= end->offset);
-    assert(!m->data_qiov || m->data_qiov->size == data_bytes);
 
     if ((start->nb_bytes == 0 && end->nb_bytes == 0) || m->skip_cow) {
         return 0;
@@ -860,7 +860,11 @@ static int perform_cow(BlockDriverState *bs, QCowL2Meta *m)
     /* The part of the buffer where the end region is located */
     end_buffer = start_buffer + buffer_size - end->nb_bytes;
 
-    qemu_iovec_init(&qiov, 2 + (m->data_qiov ? m->data_qiov->niov : 0));
+    qemu_iovec_init(&qiov, 2 + (m->data_qiov ?
+                                qemu_iovec_subvec_niov(m->data_qiov,
+                                                       m->data_qiov_offset,
+                                                       data_bytes)
+                                : 0));
 
     qemu_co_mutex_unlock(&s->lock);
     /* First we read the existing data from both COW regions. We
@@ -903,7 +907,7 @@ static int perform_cow(BlockDriverState *bs, QCowL2Meta *m)
         if (start->nb_bytes) {
             qemu_iovec_add(&qiov, start_buffer, start->nb_bytes);
         }
-        qemu_iovec_concat(&qiov, m->data_qiov, 0, data_bytes);
+        qemu_iovec_concat(&qiov, m->data_qiov, m->data_qiov_offset, data_bytes);
         if (end->nb_bytes) {
             qemu_iovec_add(&qiov, end_buffer, end->nb_bytes);
         }

block/qcow2.c

@@ -76,7 +76,8 @@ qcow2_co_preadv_compressed(BlockDriverState *bs,
                            uint64_t file_cluster_offset,
                            uint64_t offset,
                            uint64_t bytes,
-                           QEMUIOVector *qiov);
+                           QEMUIOVector *qiov,
+                           size_t qiov_offset);
 
 static int qcow2_probe(const uint8_t *buf, int buf_size, const char *filename)
 {
@@ -1967,21 +1968,18 @@ out:
     return ret;
 }
 
-static coroutine_fn int qcow2_co_preadv(BlockDriverState *bs, uint64_t offset,
-                                        uint64_t bytes, QEMUIOVector *qiov,
-                                        int flags)
+static coroutine_fn int qcow2_co_preadv_part(BlockDriverState *bs,
+                                             uint64_t offset, uint64_t bytes,
+                                             QEMUIOVector *qiov,
+                                             size_t qiov_offset, int flags)
 {
     BDRVQcow2State *s = bs->opaque;
     int offset_in_cluster;
     int ret;
     unsigned int cur_bytes; /* number of bytes in current iteration */
     uint64_t cluster_offset = 0;
-    uint64_t bytes_done = 0;
-    QEMUIOVector hd_qiov;
     uint8_t *cluster_data = NULL;
 
-    qemu_iovec_init(&hd_qiov, qiov->niov);
-
     while (bytes != 0) {
 
         /* prepare next request */
@@ -2000,34 +1998,31 @@ static coroutine_fn int qcow2_co_preadv(BlockDriverState *bs, uint64_t offset,
 
         offset_in_cluster = offset_into_cluster(s, offset);
 
-        qemu_iovec_reset(&hd_qiov);
-        qemu_iovec_concat(&hd_qiov, qiov, bytes_done, cur_bytes);
-
         switch (ret) {
         case QCOW2_CLUSTER_UNALLOCATED:
 
             if (bs->backing) {
                 BLKDBG_EVENT(bs->file, BLKDBG_READ_BACKING_AIO);
-                ret = bdrv_co_preadv(bs->backing, offset, cur_bytes,
-                                     &hd_qiov, 0);
+                ret = bdrv_co_preadv_part(bs->backing, offset, cur_bytes,
+                                          qiov, qiov_offset, 0);
                 if (ret < 0) {
                     goto fail;
                 }
             } else {
                 /* Note: in this case, no need to wait */
-                qemu_iovec_memset(&hd_qiov, 0, 0, cur_bytes);
+                qemu_iovec_memset(qiov, qiov_offset, 0, cur_bytes);
             }
             break;
 
         case QCOW2_CLUSTER_ZERO_PLAIN:
         case QCOW2_CLUSTER_ZERO_ALLOC:
-            qemu_iovec_memset(&hd_qiov, 0, 0, cur_bytes);
+            qemu_iovec_memset(qiov, qiov_offset, 0, cur_bytes);
             break;
 
         case QCOW2_CLUSTER_COMPRESSED:
             ret = qcow2_co_preadv_compressed(bs, cluster_offset,
                                              offset, cur_bytes,
-                                             &hd_qiov);
+                                             qiov, qiov_offset);
             if (ret < 0) {
                 goto fail;
             }
@@ -2059,19 +2054,15 @@ static coroutine_fn int qcow2_co_preadv(BlockDriverState *bs, uint64_t offset,
                 }
 
                 assert(cur_bytes <= QCOW_MAX_CRYPT_CLUSTERS * s->cluster_size);
-                qemu_iovec_reset(&hd_qiov);
-                qemu_iovec_add(&hd_qiov, cluster_data, cur_bytes);
-            }
 
-            BLKDBG_EVENT(bs->file, BLKDBG_READ_AIO);
-            ret = bdrv_co_preadv(s->data_file,
-                                 cluster_offset + offset_in_cluster,
-                                 cur_bytes, &hd_qiov, 0);
-            if (ret < 0) {
-                goto fail;
-            }
-            if (bs->encrypted) {
-                assert(s->crypto);
+                BLKDBG_EVENT(bs->file, BLKDBG_READ_AIO);
+                ret = bdrv_co_pread(s->data_file,
+                                    cluster_offset + offset_in_cluster,
+                                    cur_bytes, cluster_data, 0);
+                if (ret < 0) {
+                    goto fail;
+                }
+
                 assert((offset & (BDRV_SECTOR_SIZE - 1)) == 0);
                 assert((cur_bytes & (BDRV_SECTOR_SIZE - 1)) == 0);
                 if (qcow2_co_decrypt(bs, cluster_offset, offset,
@@ -2079,7 +2070,15 @@ static coroutine_fn int qcow2_co_preadv(BlockDriverState *bs, uint64_t offset,
                     ret = -EIO;
                     goto fail;
                 }
-                qemu_iovec_from_buf(qiov, bytes_done, cluster_data, cur_bytes);
+                qemu_iovec_from_buf(qiov, qiov_offset, cluster_data, cur_bytes);
+            } else {
+                BLKDBG_EVENT(bs->file, BLKDBG_READ_AIO);
+                ret = bdrv_co_preadv_part(s->data_file,
+                                          cluster_offset + offset_in_cluster,
+                                          cur_bytes, qiov, qiov_offset, 0);
+                if (ret < 0) {
+                    goto fail;
+                }
             }
             break;
 
@@ -2091,12 +2090,11 @@ static coroutine_fn int qcow2_co_preadv(BlockDriverState *bs, uint64_t offset,
 
         bytes -= cur_bytes;
         offset += cur_bytes;
-        bytes_done += cur_bytes;
+        qiov_offset += cur_bytes;
     }
     ret = 0;
 
 fail:
-    qemu_iovec_destroy(&hd_qiov);
     qemu_vfree(cluster_data);
 
     return ret;
@@ -2105,7 +2103,8 @@ fail:
 /* Check if it's possible to merge a write request with the writing of
  * the data from the COW regions */
 static bool merge_cow(uint64_t offset, unsigned bytes,
-                      QEMUIOVector *hd_qiov, QCowL2Meta *l2meta)
+                      QEMUIOVector *qiov, size_t qiov_offset,
+                      QCowL2Meta *l2meta)
 {
     QCowL2Meta *m;
 
@@ -2134,11 +2133,12 @@ static bool merge_cow(uint64_t offset, unsigned bytes,
 
         /* Make sure that adding both COW regions to the QEMUIOVector
          * does not exceed IOV_MAX */
-        if (hd_qiov->niov > IOV_MAX - 2) {
+        if (qemu_iovec_subvec_niov(qiov, qiov_offset, bytes) > IOV_MAX - 2) {
             continue;
         }
 
-        m->data_qiov = hd_qiov;
+        m->data_qiov = qiov;
+        m->data_qiov_offset = qiov_offset;
         return true;
     }
 
@@ -2220,24 +2220,22 @@ static int handle_alloc_space(BlockDriverState *bs, QCowL2Meta *l2meta)
     return 0;
 }
 
-static coroutine_fn int qcow2_co_pwritev(BlockDriverState *bs, uint64_t offset,
-                                         uint64_t bytes, QEMUIOVector *qiov,
-                                         int flags)
+static coroutine_fn int qcow2_co_pwritev_part(
+        BlockDriverState *bs, uint64_t offset, uint64_t bytes,
+        QEMUIOVector *qiov, size_t qiov_offset, int flags)
 {
     BDRVQcow2State *s = bs->opaque;
     int offset_in_cluster;
     int ret;
     unsigned int cur_bytes; /* number of sectors in current iteration */
     uint64_t cluster_offset;
-    QEMUIOVector hd_qiov;
+    QEMUIOVector encrypted_qiov;
     uint64_t bytes_done = 0;
     uint8_t *cluster_data = NULL;
     QCowL2Meta *l2meta = NULL;
 
     trace_qcow2_writev_start_req(qemu_coroutine_self(), offset, bytes);
 
-    qemu_iovec_init(&hd_qiov, qiov->niov);
-
     qemu_co_mutex_lock(&s->lock);
 
     while (bytes != 0) {
@@ -2270,9 +2268,6 @@ static coroutine_fn int qcow2_co_pwritev(BlockDriverState *bs, uint64_t offset,
 
         qemu_co_mutex_unlock(&s->lock);
 
-        qemu_iovec_reset(&hd_qiov);
-        qemu_iovec_concat(&hd_qiov, qiov, bytes_done, cur_bytes);
-
         if (bs->encrypted) {
             assert(s->crypto);
             if (!cluster_data) {
@@ -2285,9 +2280,9 @@ static coroutine_fn int qcow2_co_pwritev(BlockDriverState *bs, uint64_t offset,
                 }
             }
 
-            assert(hd_qiov.size <=
-                   QCOW_MAX_CRYPT_CLUSTERS * s->cluster_size);
-            qemu_iovec_to_buf(&hd_qiov, 0, cluster_data, hd_qiov.size);
+            assert(cur_bytes <= QCOW_MAX_CRYPT_CLUSTERS * s->cluster_size);
+            qemu_iovec_to_buf(qiov, qiov_offset + bytes_done,
+                              cluster_data, cur_bytes);
 
             if (qcow2_co_encrypt(bs, cluster_offset, offset,
                                  cluster_data, cur_bytes) < 0) {
@@ -2295,8 +2290,7 @@ static coroutine_fn int qcow2_co_pwritev(BlockDriverState *bs, uint64_t offset,
                 goto out_unlocked;
             }
 
-            qemu_iovec_reset(&hd_qiov);
-            qemu_iovec_add(&hd_qiov, cluster_data, cur_bytes);
+            qemu_iovec_init_buf(&encrypted_qiov, cluster_data, cur_bytes);
         }
 
         /* Try to efficiently initialize the physical space with zeroes */
@@ -2309,13 +2303,17 @@ static coroutine_fn int qcow2_co_pwritev(BlockDriverState *bs, uint64_t offset,
          * writing of the guest data together with that of the COW regions.
          * If it's not possible (or not necessary) then write the
          * guest data now. */
-        if (!merge_cow(offset, cur_bytes, &hd_qiov, l2meta)) {
+        if (!merge_cow(offset, cur_bytes,
+                       bs->encrypted ? &encrypted_qiov : qiov,
+                       bs->encrypted ? 0 : qiov_offset + bytes_done, l2meta))
+        {
             BLKDBG_EVENT(bs->file, BLKDBG_WRITE_AIO);
             trace_qcow2_writev_data(qemu_coroutine_self(),
                                     cluster_offset + offset_in_cluster);
-            ret = bdrv_co_pwritev(s->data_file,
-                                  cluster_offset + offset_in_cluster,
-                                  cur_bytes, &hd_qiov, 0);
+            ret = bdrv_co_pwritev_part(
+                    s->data_file, cluster_offset + offset_in_cluster, cur_bytes,
+                    bs->encrypted ? &encrypted_qiov : qiov,
+                    bs->encrypted ? 0 : qiov_offset + bytes_done, 0);
             if (ret < 0) {
                 goto out_unlocked;
             }
@@ -2344,7 +2342,6 @@ out_locked:
 
     qemu_co_mutex_unlock(&s->lock);
 
-    qemu_iovec_destroy(&hd_qiov);
     qemu_vfree(cluster_data);
     trace_qcow2_writev_done_req(qemu_coroutine_self(), ret);
 
@@ -4009,8 +4006,9 @@ fail:
 /* XXX: put compressed sectors first, then all the cluster aligned
    tables to avoid losing bytes in alignment */
 static coroutine_fn int
-qcow2_co_pwritev_compressed(BlockDriverState *bs, uint64_t offset,
-                            uint64_t bytes, QEMUIOVector *qiov)
+qcow2_co_pwritev_compressed_part(BlockDriverState *bs,
+                                 uint64_t offset, uint64_t bytes,
+                                 QEMUIOVector *qiov, size_t qiov_offset)
 {
     BDRVQcow2State *s = bs->opaque;
     int ret;
@@ -4047,7 +4045,7 @@ qcow2_co_pwritev_compressed(BlockDriverState *bs, uint64_t offset,
         /* Zero-pad last write if image size is not cluster aligned */
         memset(buf + bytes, 0, s->cluster_size - bytes);
     }
-    qemu_iovec_to_buf(qiov, 0, buf, bytes);
+    qemu_iovec_to_buf(qiov, qiov_offset, buf, bytes);
 
     out_buf = g_malloc(s->cluster_size);
 
@@ -4055,7 +4053,7 @@ qcow2_co_pwritev_compressed(BlockDriverState *bs, uint64_t offset,
                                 buf, s->cluster_size);
     if (out_len == -ENOMEM) {
         /* could not compress: write normal cluster */
-        ret = qcow2_co_pwritev(bs, offset, bytes, qiov, 0);
+        ret = qcow2_co_pwritev_part(bs, offset, bytes, qiov, qiov_offset, 0);
         if (ret < 0) {
             goto fail;
         }
@@ -4097,7 +4095,8 @@ qcow2_co_preadv_compressed(BlockDriverState *bs,
                            uint64_t file_cluster_offset,
                            uint64_t offset,
                            uint64_t bytes,
-                           QEMUIOVector *qiov)
+                           QEMUIOVector *qiov,
+                           size_t qiov_offset)
 {
     BDRVQcow2State *s = bs->opaque;
     int ret = 0, csize, nb_csectors;
@@ -4128,7 +4127,7 @@ qcow2_co_preadv_compressed(BlockDriverState *bs,
         goto fail;
     }
 
-    qemu_iovec_from_buf(qiov, 0, out_buf + offset_in_cluster, bytes);
+    qemu_iovec_from_buf(qiov, qiov_offset, out_buf + offset_in_cluster, bytes);
 
 fail:
     qemu_vfree(out_buf);
@@ -4665,8 +4664,8 @@ static int qcow2_save_vmstate(BlockDriverState *bs, QEMUIOVector *qiov,
     BDRVQcow2State *s = bs->opaque;
 
     BLKDBG_EVENT(bs->file, BLKDBG_VMSTATE_SAVE);
-    return bs->drv->bdrv_co_pwritev(bs, qcow2_vm_state_offset(s) + pos,
-                                    qiov->size, qiov, 0);
+    return bs->drv->bdrv_co_pwritev_part(bs, qcow2_vm_state_offset(s) + pos,
+                                         qiov->size, qiov, 0, 0);
 }
 
 static int qcow2_load_vmstate(BlockDriverState *bs, QEMUIOVector *qiov,
@@ -4675,8 +4674,8 @@ static int qcow2_load_vmstate(BlockDriverState *bs, QEMUIOVector *qiov,
     BDRVQcow2State *s = bs->opaque;
 
     BLKDBG_EVENT(bs->file, BLKDBG_VMSTATE_LOAD);
-    return bs->drv->bdrv_co_preadv(bs, qcow2_vm_state_offset(s) + pos,
-                                   qiov->size, qiov, 0);
+    return bs->drv->bdrv_co_preadv_part(bs, qcow2_vm_state_offset(s) + pos,
+                                        qiov->size, qiov, 0, 0);
 }
 
 /*
@@ -5218,8 +5217,8 @@ BlockDriver bdrv_qcow2 = {
     .bdrv_has_zero_init_truncate = bdrv_has_zero_init_1,
     .bdrv_co_block_status = qcow2_co_block_status,
 
-    .bdrv_co_preadv         = qcow2_co_preadv,
-    .bdrv_co_pwritev        = qcow2_co_pwritev,
+    .bdrv_co_preadv_part    = qcow2_co_preadv_part,
+    .bdrv_co_pwritev_part   = qcow2_co_pwritev_part,
     .bdrv_co_flush_to_os    = qcow2_co_flush_to_os,
 
     .bdrv_co_pwrite_zeroes  = qcow2_co_pwrite_zeroes,
@@ -5227,7 +5226,7 @@ BlockDriver bdrv_qcow2 = {
     .bdrv_co_copy_range_from = qcow2_co_copy_range_from,
     .bdrv_co_copy_range_to  = qcow2_co_copy_range_to,
     .bdrv_co_truncate       = qcow2_co_truncate,
-    .bdrv_co_pwritev_compressed = qcow2_co_pwritev_compressed,
+    .bdrv_co_pwritev_compressed_part = qcow2_co_pwritev_compressed_part,
     .bdrv_make_empty        = qcow2_make_empty,
 
     .bdrv_snapshot_create   = qcow2_snapshot_create,

block/qcow2.h

@@ -420,6 +420,7 @@ typedef struct QCowL2Meta
      * from @cow_start and @cow_end into one single write operation.
      */
     QEMUIOVector *data_qiov;
+    size_t data_qiov_offset;
 
     /** Pointer to next L2Meta of the same write request */
     struct QCowL2Meta *next;

include/block/block_int.h

@@ -210,6 +210,9 @@ struct BlockDriver {
      */
     int coroutine_fn (*bdrv_co_preadv)(BlockDriverState *bs,
         uint64_t offset, uint64_t bytes, QEMUIOVector *qiov, int flags);
+    int coroutine_fn (*bdrv_co_preadv_part)(BlockDriverState *bs,
+        uint64_t offset, uint64_t bytes,
+        QEMUIOVector *qiov, size_t qiov_offset, int flags);
     int coroutine_fn (*bdrv_co_writev)(BlockDriverState *bs,
         int64_t sector_num, int nb_sectors, QEMUIOVector *qiov, int flags);
     /**
@@ -229,6 +232,9 @@ struct BlockDriver {
      */
     int coroutine_fn (*bdrv_co_pwritev)(BlockDriverState *bs,
         uint64_t offset, uint64_t bytes, QEMUIOVector *qiov, int flags);
+    int coroutine_fn (*bdrv_co_pwritev_part)(BlockDriverState *bs,
+        uint64_t offset, uint64_t bytes,
+        QEMUIOVector *qiov, size_t qiov_offset, int flags);
 
     /*
      * Efficiently zero a region of the disk image.  Typically an image format
@@ -339,6 +345,9 @@ struct BlockDriver {
 
     int coroutine_fn (*bdrv_co_pwritev_compressed)(BlockDriverState *bs,
         uint64_t offset, uint64_t bytes, QEMUIOVector *qiov);
+    int coroutine_fn (*bdrv_co_pwritev_compressed_part)(BlockDriverState *bs,
+        uint64_t offset, uint64_t bytes, QEMUIOVector *qiov,
+        size_t qiov_offset);
 
     int (*bdrv_snapshot_create)(BlockDriverState *bs,
                                 QEMUSnapshotInfo *sn_info);
@@ -570,6 +579,12 @@ struct BlockDriver {
     const char *const *strong_runtime_opts;
 };
 
+static inline bool block_driver_can_compress(BlockDriver *drv)
+{
+    return drv->bdrv_co_pwritev_compressed ||
+           drv->bdrv_co_pwritev_compressed_part;
+}
+
 typedef struct BlockLimits {
     /* Alignment requirement, in bytes, for offset/length of I/O
      * requests. Must be a power of 2 less than INT_MAX; defaults to
@@ -944,9 +959,15 @@ extern BlockDriver bdrv_qcow2;
 int coroutine_fn bdrv_co_preadv(BdrvChild *child,
     int64_t offset, unsigned int bytes, QEMUIOVector *qiov,
     BdrvRequestFlags flags);
+int coroutine_fn bdrv_co_preadv_part(BdrvChild *child,
+    int64_t offset, unsigned int bytes,
+    QEMUIOVector *qiov, size_t qiov_offset, BdrvRequestFlags flags);
 int coroutine_fn bdrv_co_pwritev(BdrvChild *child,
     int64_t offset, unsigned int bytes, QEMUIOVector *qiov,
     BdrvRequestFlags flags);
+int coroutine_fn bdrv_co_pwritev_part(BdrvChild *child,
+    int64_t offset, unsigned int bytes,
+    QEMUIOVector *qiov, size_t qiov_offset, BdrvRequestFlags flags);
 
 static inline int coroutine_fn bdrv_co_pread(BdrvChild *child,
     int64_t offset, unsigned int bytes, void *buf, BdrvRequestFlags flags)

include/qemu/iov.h

@@ -199,13 +199,21 @@ static inline void *qemu_iovec_buf(QEMUIOVector *qiov)
 
 void qemu_iovec_init(QEMUIOVector *qiov, int alloc_hint);
 void qemu_iovec_init_external(QEMUIOVector *qiov, struct iovec *iov, int niov);
+void qemu_iovec_init_extended(
+        QEMUIOVector *qiov,
+        void *head_buf, size_t head_len,
+        QEMUIOVector *mid_qiov, size_t mid_offset, size_t mid_len,
+        void *tail_buf, size_t tail_len);
+void qemu_iovec_init_slice(QEMUIOVector *qiov, QEMUIOVector *source,
+                           size_t offset, size_t len);
+int qemu_iovec_subvec_niov(QEMUIOVector *qiov, size_t offset, size_t len);
 void qemu_iovec_add(QEMUIOVector *qiov, void *base, size_t len);
 void qemu_iovec_concat(QEMUIOVector *dst,
                        QEMUIOVector *src, size_t soffset, size_t sbytes);
 size_t qemu_iovec_concat_iov(QEMUIOVector *dst,
                              struct iovec *src_iov, unsigned int src_cnt,
                              size_t soffset, size_t sbytes);
-bool qemu_iovec_is_zero(QEMUIOVector *qiov);
+bool qemu_iovec_is_zero(QEMUIOVector *qiov, size_t qiov_offeset, size_t bytes);
 void qemu_iovec_destroy(QEMUIOVector *qiov);
 void qemu_iovec_reset(QEMUIOVector *qiov);
 size_t qemu_iovec_to_buf(QEMUIOVector *qiov, size_t offset,

qemu-img.c

@@ -2388,7 +2388,7 @@ static int img_convert(int argc, char **argv)
         const char *preallocation =
             qemu_opt_get(opts, BLOCK_OPT_PREALLOC);
 
-        if (drv && !drv->bdrv_co_pwritev_compressed) {
+        if (drv && !block_driver_can_compress(drv)) {
             error_report("Compression not supported for this file format");
             ret = -1;
             goto out;
@@ -2459,7 +2459,7 @@ static int img_convert(int argc, char **argv)
     }
     out_bs = blk_bs(s.target);
 
-    if (s.compressed && !out_bs->drv->bdrv_co_pwritev_compressed) {
+    if (s.compressed && !block_driver_can_compress(out_bs->drv)) {
         error_report("Compression not supported for this file format");
         ret = -1;
         goto out;

util/iov.c

@@ -354,34 +354,153 @@ void qemu_iovec_concat(QEMUIOVector *dst,
 }
 
 /*
- * Check if the contents of the iovecs are all zero
+ * qiov_find_iov
+ *
+ * Return pointer to iovec structure, where byte at @offset in original vector
+ * @iov exactly is.
+ * Set @remaining_offset to be offset inside that iovec to the same byte.
  */
-bool qemu_iovec_is_zero(QEMUIOVector *qiov)
+static struct iovec *iov_skip_offset(struct iovec *iov, size_t offset,
+                                     size_t *remaining_offset)
 {
-    int i;
-    for (i = 0; i < qiov->niov; i++) {
-        size_t offs = QEMU_ALIGN_DOWN(qiov->iov[i].iov_len, 4 * sizeof(long));
-        uint8_t *ptr = qiov->iov[i].iov_base;
-        if (offs && !buffer_is_zero(qiov->iov[i].iov_base, offs)) {
+    while (offset > 0 && offset >= iov->iov_len) {
+        offset -= iov->iov_len;
+        iov++;
+    }
+    *remaining_offset = offset;
+
+    return iov;
+}
+
+/*
+ * qiov_slice
+ *
+ * Find subarray of iovec's, containing requested range. @head would
+ * be offset in first iov (returned by the function), @tail would be
+ * count of extra bytes in last iovec (returned iov + @niov - 1).
+ */
+static struct iovec *qiov_slice(QEMUIOVector *qiov,
+                                size_t offset, size_t len,
+                                size_t *head, size_t *tail, int *niov)
+{
+    struct iovec *iov, *end_iov;
+
+    assert(offset + len <= qiov->size);
+
+    iov = iov_skip_offset(qiov->iov, offset, head);
+    end_iov = iov_skip_offset(iov, *head + len, tail);
+
+    if (*tail > 0) {
+        assert(*tail < end_iov->iov_len);
+        *tail = end_iov->iov_len - *tail;
+        end_iov++;
+    }
+
+    *niov = end_iov - iov;
+
+    return iov;
+}
+
+int qemu_iovec_subvec_niov(QEMUIOVector *qiov, size_t offset, size_t len)
+{
+    size_t head, tail;
+    int niov;
+
+    qiov_slice(qiov, offset, len, &head, &tail, &niov);
+
+    return niov;
+}
+
+/*
+ * Compile new iovec, combining @head_buf buffer, sub-qiov of @mid_qiov,
+ * and @tail_buf buffer into new qiov.
+ */
+void qemu_iovec_init_extended(
+        QEMUIOVector *qiov,
+        void *head_buf, size_t head_len,
+        QEMUIOVector *mid_qiov, size_t mid_offset, size_t mid_len,
+        void *tail_buf, size_t tail_len)
+{
+    size_t mid_head, mid_tail;
+    int total_niov, mid_niov = 0;
+    struct iovec *p, *mid_iov;
+
+    if (mid_len) {
+        mid_iov = qiov_slice(mid_qiov, mid_offset, mid_len,
+                             &mid_head, &mid_tail, &mid_niov);
+    }
+
+    total_niov = !!head_len + mid_niov + !!tail_len;
+    if (total_niov == 1) {
+        qemu_iovec_init_buf(qiov, NULL, 0);
+        p = &qiov->local_iov;
+    } else {
+        qiov->niov = qiov->nalloc = total_niov;
+        qiov->size = head_len + mid_len + tail_len;
+        p = qiov->iov = g_new(struct iovec, qiov->niov);
+    }
+
+    if (head_len) {
+        p->iov_base = head_buf;
+        p->iov_len = head_len;
+        p++;
+    }
+
+    if (mid_len) {
+        memcpy(p, mid_iov, mid_niov * sizeof(*p));
+        p[0].iov_base = (uint8_t *)p[0].iov_base + mid_head;
+        p[0].iov_len -= mid_head;
+        p[mid_niov - 1].iov_len -= mid_tail;
+        p += mid_niov;
+    }
+
+    if (tail_len) {
+        p->iov_base = tail_buf;
+        p->iov_len = tail_len;
+    }
+}
+
+/*
+ * Check if the contents of subrange of qiov data is all zeroes.
+ */
+bool qemu_iovec_is_zero(QEMUIOVector *qiov, size_t offset, size_t bytes)
+{
+    struct iovec *iov;
+    size_t current_offset;
+
+    assert(offset + bytes <= qiov->size);
+
+    iov = iov_skip_offset(qiov->iov, offset, &current_offset);
+
+    while (bytes) {
+        uint8_t *base = (uint8_t *)iov->iov_base + current_offset;
+        size_t len = MIN(iov->iov_len - current_offset, bytes);
+
+        if (!buffer_is_zero(base, len)) {
             return false;
         }
-        for (; offs < qiov->iov[i].iov_len; offs++) {
-            if (ptr[offs]) {
-                return false;
-            }
-        }
+
+        current_offset = 0;
+        bytes -= len;
+        iov++;
     }
+
     return true;
 }
 
+void qemu_iovec_init_slice(QEMUIOVector *qiov, QEMUIOVector *source,
+                           size_t offset, size_t len)
+{
+    qemu_iovec_init_extended(qiov, NULL, 0, source, offset, len, NULL, 0);
+}
+
 void qemu_iovec_destroy(QEMUIOVector *qiov)
 {
-    assert(qiov->nalloc != -1);
+    if (qiov->nalloc != -1) {
+        g_free(qiov->iov);
+    }
 
-    qemu_iovec_reset(qiov);
-    g_free(qiov->iov);
-    qiov->nalloc = 0;
-    qiov->iov = NULL;
+    memset(qiov, 0, sizeof(*qiov));
 }
 
 void qemu_iovec_reset(QEMUIOVector *qiov)