block/qcow2: refactor qcow2_co_pwritev_part

Similarly to previous commit, prepare for parallelizing write-loop
iterations.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Message-id: 20190916175324.18478-5-vsementsov@virtuozzo.com
Signed-off-by: Max Reitz <mreitz@redhat.com>

block/qcow2.c

@@ -2242,6 +2242,88 @@ static int handle_alloc_space(BlockDriverState *bs, QCowL2Meta *l2meta)
     return 0;
 }
 
+/*
+ * qcow2_co_pwritev_task
+ * Called with s->lock unlocked
+ * l2meta  - if not NULL, qcow2_co_pwritev_task() will consume it. Caller must
+ *           not use it somehow after qcow2_co_pwritev_task() call
+ */
+static coroutine_fn int qcow2_co_pwritev_task(BlockDriverState *bs,
+                                              uint64_t file_cluster_offset,
+                                              uint64_t offset, uint64_t bytes,
+                                              QEMUIOVector *qiov,
+                                              uint64_t qiov_offset,
+                                              QCowL2Meta *l2meta)
+{
+    int ret;
+    BDRVQcow2State *s = bs->opaque;
+    void *crypt_buf = NULL;
+    int offset_in_cluster = offset_into_cluster(s, offset);
+    QEMUIOVector encrypted_qiov;
+
+    if (bs->encrypted) {
+        assert(s->crypto);
+        assert(bytes <= QCOW_MAX_CRYPT_CLUSTERS * s->cluster_size);
+        crypt_buf = qemu_try_blockalign(bs->file->bs, bytes);
+        if (crypt_buf == NULL) {
+            ret = -ENOMEM;
+            goto out_unlocked;
+        }
+        qemu_iovec_to_buf(qiov, qiov_offset, crypt_buf, bytes);
+
+        if (qcow2_co_encrypt(bs, file_cluster_offset + offset_in_cluster,
+                             offset, crypt_buf, bytes) < 0)
+        {
+            ret = -EIO;
+            goto out_unlocked;
+        }
+
+        qemu_iovec_init_buf(&encrypted_qiov, crypt_buf, bytes);
+        qiov = &encrypted_qiov;
+        qiov_offset = 0;
+    }
+
+    /* Try to efficiently initialize the physical space with zeroes */
+    ret = handle_alloc_space(bs, l2meta);
+    if (ret < 0) {
+        goto out_unlocked;
+    }
+
+    /*
+     * If we need to do COW, check if it's possible to merge the
+     * 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, bytes, qiov, qiov_offset, l2meta)) {
+        BLKDBG_EVENT(bs->file, BLKDBG_WRITE_AIO);
+        trace_qcow2_writev_data(qemu_coroutine_self(),
+                                file_cluster_offset + offset_in_cluster);
+        ret = bdrv_co_pwritev_part(s->data_file,
+                                   file_cluster_offset + offset_in_cluster,
+                                   bytes, qiov, qiov_offset, 0);
+        if (ret < 0) {
+            goto out_unlocked;
+        }
+    }
+
+    qemu_co_mutex_lock(&s->lock);
+
+    ret = qcow2_handle_l2meta(bs, &l2meta, true);
+    goto out_locked;
+
+out_unlocked:
+    qemu_co_mutex_lock(&s->lock);
+
+out_locked:
+    qcow2_handle_l2meta(bs, &l2meta, false);
+    qemu_co_mutex_unlock(&s->lock);
+
+    qemu_vfree(crypt_buf);
+
+    return ret;
+}
+
 static coroutine_fn int qcow2_co_pwritev_part(
         BlockDriverState *bs, uint64_t offset, uint64_t bytes,
         QEMUIOVector *qiov, size_t qiov_offset, int flags)
@@ -2251,15 +2333,10 @@ static coroutine_fn int qcow2_co_pwritev_part(
     int ret;
     unsigned int cur_bytes; /* number of sectors in current iteration */
     uint64_t cluster_offset;
-    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_co_mutex_lock(&s->lock);
-
     while (bytes != 0) {
 
         l2meta = NULL;
@@ -2273,6 +2350,8 @@ static coroutine_fn int qcow2_co_pwritev_part(
                             - offset_in_cluster);
         }
 
+        qemu_co_mutex_lock(&s->lock);
+
         ret = qcow2_alloc_cluster_offset(bs, offset, &cur_bytes,
                                          &cluster_offset, &l2meta);
         if (ret < 0) {
@@ -2290,73 +2369,20 @@ static coroutine_fn int qcow2_co_pwritev_part(
 
         qemu_co_mutex_unlock(&s->lock);
 
-        if (bs->encrypted) {
+        ret = qcow2_co_pwritev_task(bs, cluster_offset, offset, cur_bytes,
-            assert(s->crypto);
+                                    qiov, qiov_offset, l2meta);
-            if (!cluster_data) {
+        l2meta = NULL; /* l2meta is consumed by qcow2_co_pwritev_task() */
-                cluster_data = qemu_try_blockalign(bs->file->bs,
-                                                   QCOW_MAX_CRYPT_CLUSTERS
-                                                   * s->cluster_size);
-                if (cluster_data == NULL) {
-                    ret = -ENOMEM;
-                    goto out_unlocked;
-                }
-            }
-
-            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_in_cluster, offset,
-                                 cluster_data, cur_bytes) < 0) {
-                ret = -EIO;
-                goto out_unlocked;
-            }
-
-            qemu_iovec_init_buf(&encrypted_qiov, cluster_data, cur_bytes);
-        }
-
-        /* Try to efficiently initialize the physical space with zeroes */
-        ret = handle_alloc_space(bs, l2meta);
         if (ret < 0) {
-            goto out_unlocked;
+            goto fail_nometa;
-        }
-
-        /* If we need to do COW, check if it's possible to merge the
-         * 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,
-                       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_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;
-            }
-        }
-
-        qemu_co_mutex_lock(&s->lock);
-
-        ret = qcow2_handle_l2meta(bs, &l2meta, true);
-        if (ret) {
-            goto out_locked;
         }
 
         bytes -= cur_bytes;
         offset += cur_bytes;
-        bytes_done += cur_bytes;
+        qiov_offset += cur_bytes;
         trace_qcow2_writev_done_part(qemu_coroutine_self(), cur_bytes);
     }
     ret = 0;
-    goto out_locked;
 
-out_unlocked:
     qemu_co_mutex_lock(&s->lock);
 
 out_locked:
@@ -2364,7 +2390,7 @@ out_locked:
 
     qemu_co_mutex_unlock(&s->lock);
 
-    qemu_vfree(cluster_data);
+fail_nometa:
     trace_qcow2_writev_done_req(qemu_coroutine_self(), ret);
 
     return ret;