block: Use blk_co_pdiscard() for all BB level discard

All read/write functions already have a single coroutine-based function
on the BlockBackend level through which all requests go (no matter what
API style the external caller used) and which passes the requests down
to the block node level.

This patch extends this mode of operation to discards.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>

block/block-backend.c

@@ -1114,16 +1114,21 @@ BlockAIOCB *blk_aio_flush(BlockBackend *blk,
     return blk_aio_prwv(blk, 0, 0, NULL, blk_aio_flush_entry, 0, cb, opaque);
 }
 
+static void blk_aio_pdiscard_entry(void *opaque)
+{
+    BlkAioEmAIOCB *acb = opaque;
+    BlkRwCo *rwco = &acb->rwco;
+
+    rwco->ret = blk_co_pdiscard(rwco->blk, rwco->offset, acb->bytes);
+    blk_aio_complete(acb);
+}
+
 BlockAIOCB *blk_aio_pdiscard(BlockBackend *blk,
                              int64_t offset, int count,
                              BlockCompletionFunc *cb, void *opaque)
 {
-    int ret = blk_check_byte_request(blk, offset, count);
-    if (ret < 0) {
-        return blk_abort_aio_request(blk, cb, opaque, ret);
-    }
-
-    return bdrv_aio_pdiscard(blk_bs(blk), offset, count, cb, opaque);
+    return blk_aio_prwv(blk, offset, count, NULL, blk_aio_pdiscard_entry, 0,
+                        cb, opaque);
 }
 
 void blk_aio_cancel(BlockAIOCB *acb)
@@ -1562,14 +1567,15 @@ int blk_truncate(BlockBackend *blk, int64_t offset)
     return bdrv_truncate(blk_bs(blk), offset);
 }
 
-int blk_pdiscard(BlockBackend *blk, int64_t offset, int count)
+static void blk_pdiscard_entry(void *opaque)
 {
-    int ret = blk_check_byte_request(blk, offset, count);
-    if (ret < 0) {
-        return ret;
-    }
+    BlkRwCo *rwco = opaque;
+    rwco->ret = blk_co_pdiscard(rwco->blk, rwco->offset, rwco->qiov->size);
+}
 
-    return bdrv_pdiscard(blk_bs(blk), offset, count);
+int blk_pdiscard(BlockBackend *blk, int64_t offset, int count)
+{
+    return blk_prw(blk, offset, NULL, count, blk_pdiscard_entry, 0);
 }
 
 int blk_save_vmstate(BlockBackend *blk, const uint8_t *buf,