block: Use blk_co_preadv() for blk_read()

This patch introduces blk_co_preadv() as a central function on the
BlockBackend level that is supposed to handle all read requests from the
BB to its root BDS eventually.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>

block/block-backend.c

@@ -22,6 +22,8 @@
 /* Number of coroutines to reserve per attached device model */
 #define COROUTINE_POOL_RESERVATION 64
 
+#define NOT_DONE 0x7fffffff /* used while emulated sync operation in progress */
+
 static AioContext *blk_aiocb_get_aio_context(BlockAIOCB *acb);
 
 struct BlockBackend {
@@ -693,15 +695,69 @@ static int blk_check_request(BlockBackend *blk, int64_t sector_num,
                                   nb_sectors * BDRV_SECTOR_SIZE);
 }
 
-int blk_read(BlockBackend *blk, int64_t sector_num, uint8_t *buf,
+static int coroutine_fn blk_co_preadv(BlockBackend *blk, int64_t offset,
-             int nb_sectors)
+                                      unsigned int bytes, QEMUIOVector *qiov,
+                                      BdrvRequestFlags flags)
 {
-    int ret = blk_check_request(blk, sector_num, nb_sectors);
+    int ret = blk_check_byte_request(blk, offset, bytes);
     if (ret < 0) {
         return ret;
     }
 
-    return bdrv_read(blk_bs(blk), sector_num, buf, nb_sectors);
+    return bdrv_co_do_preadv(blk_bs(blk), offset, bytes, qiov, flags);
+}
+
+typedef struct BlkRwCo {
+    BlockBackend *blk;
+    int64_t offset;
+    QEMUIOVector *qiov;
+    int ret;
+    BdrvRequestFlags flags;
+} BlkRwCo;
+
+static void blk_read_entry(void *opaque)
+{
+    BlkRwCo *rwco = opaque;
+
+    rwco->ret = blk_co_preadv(rwco->blk, rwco->offset, rwco->qiov->size,
+                              rwco->qiov, rwco->flags);
+}
+
+int blk_read(BlockBackend *blk, int64_t sector_num, uint8_t *buf,
+             int nb_sectors)
+{
+    AioContext *aio_context;
+    QEMUIOVector qiov;
+    struct iovec iov;
+    Coroutine *co;
+    BlkRwCo rwco;
+
+    if (nb_sectors < 0 || nb_sectors > BDRV_REQUEST_MAX_SECTORS) {
+        return -EINVAL;
+    }
+
+    iov = (struct iovec) {
+        .iov_base = buf,
+        .iov_len = nb_sectors * BDRV_SECTOR_SIZE,
+    };
+    qemu_iovec_init_external(&qiov, &iov, 1);
+
+    rwco = (BlkRwCo) {
+        .blk    = blk,
+        .offset = sector_num << BDRV_SECTOR_BITS,
+        .qiov   = &qiov,
+        .ret    = NOT_DONE,
+    };
+
+    co = qemu_coroutine_create(blk_read_entry);
+    qemu_coroutine_enter(co, &rwco);
+
+    aio_context = blk_get_aio_context(blk);
+    while (rwco.ret == NOT_DONE) {
+        aio_poll(aio_context, true);
+    }
+
+    return rwco.ret;
 }
 
 int blk_read_unthrottled(BlockBackend *blk, int64_t sector_num, uint8_t *buf,

block/io.c

@@ -44,9 +44,6 @@ static int coroutine_fn bdrv_co_readv_em(BlockDriverState *bs,
 static int coroutine_fn bdrv_co_writev_em(BlockDriverState *bs,
                                          int64_t sector_num, int nb_sectors,
                                          QEMUIOVector *iov);
-static int coroutine_fn bdrv_co_do_preadv(BlockDriverState *bs,
-    int64_t offset, unsigned int bytes, QEMUIOVector *qiov,
-    BdrvRequestFlags flags);
 static int coroutine_fn bdrv_co_do_pwritev(BlockDriverState *bs,
     int64_t offset, unsigned int bytes, QEMUIOVector *qiov,
     BdrvRequestFlags flags);
@@ -939,7 +936,7 @@ out:
 /*
  * Handle a read request in coroutine context
  */
-static int coroutine_fn bdrv_co_do_preadv(BlockDriverState *bs,
+int coroutine_fn bdrv_co_do_preadv(BlockDriverState *bs,
     int64_t offset, unsigned int bytes, QEMUIOVector *qiov,
     BdrvRequestFlags flags)
 {

include/block/block_int.h

@@ -508,6 +508,10 @@ extern BlockDriver bdrv_qcow2;
  */
 void bdrv_setup_io_funcs(BlockDriver *bdrv);
 
+int coroutine_fn bdrv_co_do_preadv(BlockDriverState *bs,
+    int64_t offset, unsigned int bytes, QEMUIOVector *qiov,
+    BdrvRequestFlags flags);
+
 int get_tmp_filename(char *filename, int size);
 BlockDriver *bdrv_probe_all(const uint8_t *buf, int buf_size,
                             const char *filename);