block/io: support int64_t bytes in bdrv_aligned_preadv()

We are generally moving to int64_t for both offset and bytes parameters
on all io paths.

Main motivation is realization of 64-bit write_zeroes operation for
fast zeroing large disk chunks, up to the whole disk.

We chose signed type, to be consistent with off_t (which is signed) and
with possibility for signed return type (where negative value means
error).

So, prepare bdrv_aligned_preadv() now.

Make the bytes variable in bdrv_padding_rmw_read() int64_t, as it is
only used for pass-through to bdrv_aligned_preadv().

All bdrv_aligned_preadv() callers are safe as type is widening. Let's
look inside:

 - add a new-style assertion that request is good.
 - callees bdrv_is_allocated(), bdrv_co_do_copy_on_readv() supports
   int64_t bytes
 - conversion of bytes_remaining is OK, as we never have requests
   overflowing BDRV_MAX_LENGTH
 - looping through bytes_remaining is ok, num is updated to int64_t
   - for bdrv_driver_preadv we have same limit of max_transfer
   - qemu_iovec_memset is OK, as bytes+qiov_offset should not overflow
     qiov->size anyway (thanks to bdrv_check_qiov_request())

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Message-Id: <20201211183934.169161-14-vsementsov@virtuozzo.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
[eblake: grammar tweak]
Signed-off-by: Eric Blake <eblake@redhat.com>

block/io.c

@@ -1475,15 +1475,16 @@ static int coroutine_fn bdrv_co_do_copy_on_readv(BdrvChild *child,
  * reads; any other features must be implemented by the caller.
  */
 static int coroutine_fn bdrv_aligned_preadv(BdrvChild *child,
-    BdrvTrackedRequest *req, int64_t offset, unsigned int bytes,
+    BdrvTrackedRequest *req, int64_t offset, int64_t bytes,
     int64_t align, QEMUIOVector *qiov, size_t qiov_offset, int flags)
 {
     BlockDriverState *bs = child->bs;
     int64_t total_bytes, max_bytes;
     int ret = 0;
-    uint64_t bytes_remaining = bytes;
+    int64_t bytes_remaining = bytes;
     int max_transfer;
 
+    bdrv_check_qiov_request(offset, bytes, qiov, qiov_offset, &error_abort);
     assert(is_power_of_2(align));
     assert((offset & (align - 1)) == 0);
     assert((bytes & (align - 1)) == 0);
@@ -1545,7 +1546,7 @@ static int coroutine_fn bdrv_aligned_preadv(BdrvChild *child,
     }
 
     while (bytes_remaining) {
-        int num;
+        int64_t num;
 
         if (max_bytes) {
             num = MIN(bytes_remaining, MIN(max_bytes, max_transfer));
@@ -1652,7 +1653,7 @@ static int bdrv_padding_rmw_read(BdrvChild *child,
     assert(req->serialising && pad->buf);
 
     if (pad->head || pad->merge_reads) {
-        uint64_t bytes = pad->merge_reads ? pad->buf_len : align;
+        int64_t bytes = pad->merge_reads ? pad->buf_len : align;
 
         qemu_iovec_init_buf(&local_qiov, pad->buf, bytes);