block: Introduce bdrv_pwritev() for qcow2_save_vmstate

Directly pass the QEMUIOVector on instead of linearising it.
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

block.c

@@ -2131,27 +2131,21 @@ static void coroutine_fn bdrv_rw_co_entry(void *opaque)
 }
 
 /*
- * Process a synchronous request using coroutines
+ * Process a vectored synchronous request using coroutines
  */
-static int bdrv_rw_co(BlockDriverState *bs, int64_t sector_num, uint8_t *buf,
-                      int nb_sectors, bool is_write)
+static int bdrv_rwv_co(BlockDriverState *bs, int64_t sector_num,
+                       QEMUIOVector *qiov, bool is_write)
 {
-    QEMUIOVector qiov;
-    struct iovec iov = {
-        .iov_base = (void *)buf,
-        .iov_len = nb_sectors * BDRV_SECTOR_SIZE,
-    };
     Coroutine *co;
     RwCo rwco = {
         .bs = bs,
         .sector_num = sector_num,
-        .nb_sectors = nb_sectors,
-        .qiov = &qiov,
+        .nb_sectors = qiov->size >> BDRV_SECTOR_BITS,
+        .qiov = qiov,
         .is_write = is_write,
         .ret = NOT_DONE,
     };
-
-    qemu_iovec_init_external(&qiov, &iov, 1);
+    assert((qiov->size & (BDRV_SECTOR_SIZE - 1)) == 0);
 
     /**
      * In sync call context, when the vcpu is blocked, this throttling timer
@@ -2177,6 +2171,22 @@ static int bdrv_rw_co(BlockDriverState *bs, int64_t sector_num, uint8_t *buf,
     return rwco.ret;
 }
 
+/*
+ * Process a synchronous request using coroutines
+ */
+static int bdrv_rw_co(BlockDriverState *bs, int64_t sector_num, uint8_t *buf,
+                      int nb_sectors, bool is_write)
+{
+    QEMUIOVector qiov;
+    struct iovec iov = {
+        .iov_base = (void *)buf,
+        .iov_len = nb_sectors * BDRV_SECTOR_SIZE,
+    };
+
+    qemu_iovec_init_external(&qiov, &iov, 1);
+    return bdrv_rwv_co(bs, sector_num, &qiov, is_write);
+}
+
 /* return < 0 if error. See bdrv_write() for the return codes */
 int bdrv_read(BlockDriverState *bs, int64_t sector_num,
               uint8_t *buf, int nb_sectors)
@@ -2210,6 +2220,11 @@ int bdrv_write(BlockDriverState *bs, int64_t sector_num,
     return bdrv_rw_co(bs, sector_num, (uint8_t *)buf, nb_sectors, true);
 }
 
+int bdrv_writev(BlockDriverState *bs, int64_t sector_num, QEMUIOVector *qiov)
+{
+    return bdrv_rwv_co(bs, sector_num, qiov, true);
+}
+
 int bdrv_pread(BlockDriverState *bs, int64_t offset,
                void *buf, int count1)
 {
@@ -2255,15 +2270,15 @@ int bdrv_pread(BlockDriverState *bs, int64_t offset,
     return count1;
 }
 
-int bdrv_pwrite(BlockDriverState *bs, int64_t offset,
-                const void *buf, int count1)
+int bdrv_pwritev(BlockDriverState *bs, int64_t offset, QEMUIOVector *qiov)
 {
     uint8_t tmp_buf[BDRV_SECTOR_SIZE];
     int len, nb_sectors, count;
     int64_t sector_num;
     int ret;
 
-    count = count1;
+    count = qiov->size;
+
     /* first write to align to sector start */
     len = (BDRV_SECTOR_SIZE - offset) & (BDRV_SECTOR_SIZE - 1);
     if (len > count)
@@ -2272,24 +2287,32 @@ int bdrv_pwrite(BlockDriverState *bs, int64_t offset,
     if (len > 0) {
         if ((ret = bdrv_read(bs, sector_num, tmp_buf, 1)) < 0)
             return ret;
-        memcpy(tmp_buf + (offset & (BDRV_SECTOR_SIZE - 1)), buf, len);
+        qemu_iovec_to_buf(qiov, 0, tmp_buf + (offset & (BDRV_SECTOR_SIZE - 1)),
+                          len);
         if ((ret = bdrv_write(bs, sector_num, tmp_buf, 1)) < 0)
             return ret;
         count -= len;
         if (count == 0)
-            return count1;
+            return qiov->size;
         sector_num++;
-        buf += len;
     }
 
     /* write the sectors "in place" */
     nb_sectors = count >> BDRV_SECTOR_BITS;
     if (nb_sectors > 0) {
-        if ((ret = bdrv_write(bs, sector_num, buf, nb_sectors)) < 0)
+        QEMUIOVector qiov_inplace;
+
+        qemu_iovec_init(&qiov_inplace, qiov->niov);
+        qemu_iovec_concat(&qiov_inplace, qiov, len,
+                          nb_sectors << BDRV_SECTOR_BITS);
+        ret = bdrv_writev(bs, sector_num, &qiov_inplace);
+        qemu_iovec_destroy(&qiov_inplace);
+        if (ret < 0) {
             return ret;
+        }
+
         sector_num += nb_sectors;
         len = nb_sectors << BDRV_SECTOR_BITS;
-        buf += len;
         count -= len;
     }
 
@@ -2297,11 +2320,24 @@ int bdrv_pwrite(BlockDriverState *bs, int64_t offset,
     if (count > 0) {
         if ((ret = bdrv_read(bs, sector_num, tmp_buf, 1)) < 0)
             return ret;
-        memcpy(tmp_buf, buf, count);
+        qemu_iovec_to_buf(qiov, qiov->size - count, tmp_buf, count);
         if ((ret = bdrv_write(bs, sector_num, tmp_buf, 1)) < 0)
             return ret;
     }
-    return count1;
+    return qiov->size;
+}
+
+int bdrv_pwrite(BlockDriverState *bs, int64_t offset,
+                const void *buf, int count1)
+{
+    QEMUIOVector qiov;
+    struct iovec iov = {
+        .iov_base   = (void *) buf,
+        .iov_len    = count1,
+    };
+
+    qemu_iovec_init_external(&qiov, &iov, 1);
+    return bdrv_pwritev(bs, offset, &qiov);
 }
 
 /*

block/qcow2.c

@@ -1658,18 +1658,12 @@ static int qcow2_save_vmstate(BlockDriverState *bs, QEMUIOVector *qiov,
     BDRVQcowState *s = bs->opaque;
     int growable = bs->growable;
     int ret;
-    void *buf;
-
-    buf = qemu_blockalign(bs, qiov->size);
-    qemu_iovec_to_buf(qiov, 0, buf, qiov->size);
 
     BLKDBG_EVENT(bs->file, BLKDBG_VMSTATE_SAVE);
     bs->growable = 1;
-    ret = bdrv_pwrite(bs, qcow2_vm_state_offset(s) + pos, buf, qiov->size);
+    ret = bdrv_pwritev(bs, qcow2_vm_state_offset(s) + pos, qiov);
     bs->growable = growable;
 
-    qemu_vfree(buf);
-
     return ret;
 }
 

include/block/block.h

@@ -166,10 +166,12 @@ int bdrv_read_unthrottled(BlockDriverState *bs, int64_t sector_num,
                           uint8_t *buf, int nb_sectors);
 int bdrv_write(BlockDriverState *bs, int64_t sector_num,
                const uint8_t *buf, int nb_sectors);
+int bdrv_writev(BlockDriverState *bs, int64_t sector_num, QEMUIOVector *qiov);
 int bdrv_pread(BlockDriverState *bs, int64_t offset,
                void *buf, int count);
 int bdrv_pwrite(BlockDriverState *bs, int64_t offset,
                 const void *buf, int count);
+int bdrv_pwritev(BlockDriverState *bs, int64_t offset, QEMUIOVector *qiov);
 int bdrv_pwrite_sync(BlockDriverState *bs, int64_t offset,
     const void *buf, int count);
 int coroutine_fn bdrv_co_readv(BlockDriverState *bs, int64_t sector_num,