@@ -971,21 +971,25 @@ err:
/*
* Forwards an already correctly aligned request to the BlockDriver. This
- * handles copy on read and zeroing after EOF; any other features must be
- * implemented by the caller.
+ * handles copy on read, zeroing after EOF, and fragmentation of large
+ * reads; any other features must be implemented by the caller.
*/
static int coroutine_fn bdrv_aligned_preadv(BlockDriverState *bs,
BdrvTrackedRequest *req, int64_t offset, unsigned int bytes,
int64_t align, QEMUIOVector *qiov, int flags)
{
int64_t total_bytes, max_bytes;
- int ret;
+ int ret = 0;
+ uint64_t bytes_remaining = bytes;
+ int max_transfer;
assert(is_power_of_2(align));
assert((offset & (align - 1)) == 0);
assert((bytes & (align - 1)) == 0);
assert(!qiov || bytes == qiov->size);
assert((bs->open_flags & BDRV_O_NO_IO) == 0);
+ max_transfer = QEMU_ALIGN_DOWN(MIN_NON_ZERO(bs->bl.max_transfer, INT_MAX),
+ align);
/* TODO: We would need a per-BDS .supported_read_flags and
* potential fallback support, if we ever implement any read flags
@@ -1024,7 +1028,7 @@ static int coroutine_fn bdrv_aligned_preadv(BlockDriverState *bs,
}
}
- /* Forward the request to the BlockDriver */
+ /* Forward the request to the BlockDriver, possibly fragmenting it */
total_bytes = bdrv_getlength(bs);
if (total_bytes < 0) {
ret = total_bytes;
@@ -1032,30 +1036,39 @@ static int coroutine_fn bdrv_aligned_preadv(BlockDriverState *bs,
}
max_bytes = ROUND_UP(MAX(0, total_bytes - offset), align);
- if (bytes <= max_bytes) {
+ if (bytes <= max_bytes && bytes <= max_transfer) {
ret = bdrv_driver_preadv(bs, offset, bytes, qiov, 0);
- } else if (max_bytes > 0) {
- QEMUIOVector local_qiov;
-
- qemu_iovec_init(&local_qiov, qiov->niov);
- qemu_iovec_concat(&local_qiov, qiov, 0, max_bytes);
-
- ret = bdrv_driver_preadv(bs, offset, max_bytes, &local_qiov, 0);
-
- qemu_iovec_destroy(&local_qiov);
- } else {
- ret = 0;
+ goto out;
}
- /* Reading beyond end of file is supposed to produce zeroes */
- if (ret == 0 && total_bytes < offset + bytes) {
- uint64_t zero_offset = MAX(0, total_bytes - offset);
- uint64_t zero_bytes = offset + bytes - zero_offset;
- qemu_iovec_memset(qiov, zero_offset, 0, zero_bytes);
+ while (bytes_remaining) {
+ int num;
+
+ if (max_bytes) {
+ QEMUIOVector local_qiov;
+
+ num = MIN(bytes_remaining, MIN(max_bytes, max_transfer));
+ assert(num);
+ qemu_iovec_init(&local_qiov, qiov->niov);
+ qemu_iovec_concat(&local_qiov, qiov, bytes - bytes_remaining, num);
+
+ ret = bdrv_driver_preadv(bs, offset + bytes - bytes_remaining,
+ num, &local_qiov, 0);
+ max_bytes -= num;
+ qemu_iovec_destroy(&local_qiov);
+ } else {
+ num = bytes_remaining;
+ ret = qemu_iovec_memset(qiov, bytes - bytes_remaining, 0,
+ bytes_remaining);
+ }
+ if (ret < 0) {
+ goto out;
+ }
+ bytes_remaining -= num;
}
out:
- return ret;
+ return ret < 0 ? ret : 0;
}
/*