block/io: support int64_t bytes in bdrv_co_do_pwrite_zeroes()

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_co_do_pwrite_zeroes() now.

Callers are safe, as converting int to int64_t is safe. Concentrate on
'bytes' usage in the function (thx to Eric Blake):

    compute 'int tail' via % 'int alignment' - safe
    fragmentation loop 'int num' - still fragments with a cap on
      max_transfer

    use of 'num' within the loop
    MIN(bytes, max_transfer) as well as %alignment - still works, so
         calculations in if (head) {} are safe
    clamp size by 'int max_write_zeroes' - safe
    drv->bdrv_co_pwrite_zeroes(int) - safe because of clamping
    clamp size by 'int max_transfer' - safe
    buf allocation is still clamped to max_transfer
    qemu_iovec_init_buf(size_t) - safe because of clamping
    bdrv_driver_pwritev(uint64_t) - safe

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Message-Id: <20201211183934.169161-11-vsementsov@virtuozzo.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Eric Blake <eblake@redhat.com>

block/io.c

@@ -41,7 +41,7 @@
 
 static void bdrv_parent_cb_resize(BlockDriverState *bs);
 static int coroutine_fn bdrv_co_do_pwrite_zeroes(BlockDriverState *bs,
-    int64_t offset, int bytes, BdrvRequestFlags flags);
+    int64_t offset, int64_t bytes, BdrvRequestFlags flags);
 
 static void bdrv_parent_drained_begin(BlockDriverState *bs, BdrvChild *ignore,
                                       bool ignore_bds_parents)
@@ -1819,7 +1819,7 @@ int coroutine_fn bdrv_co_preadv_part(BdrvChild *child,
 }
 
 static int coroutine_fn bdrv_co_do_pwrite_zeroes(BlockDriverState *bs,
-    int64_t offset, int bytes, BdrvRequestFlags flags)
+    int64_t offset, int64_t bytes, BdrvRequestFlags flags)
 {
     BlockDriver *drv = bs->drv;
     QEMUIOVector qiov;
@@ -1834,6 +1834,8 @@ static int coroutine_fn bdrv_co_do_pwrite_zeroes(BlockDriverState *bs,
                         bs->bl.request_alignment);
     int max_transfer = MIN_NON_ZERO(bs->bl.max_transfer, MAX_BOUNCE_BUFFER);
 
+    bdrv_check_request(offset, bytes, &error_abort);
+
     if (!drv) {
         return -ENOMEDIUM;
     }
@@ -1849,7 +1851,7 @@ static int coroutine_fn bdrv_co_do_pwrite_zeroes(BlockDriverState *bs,
     assert(max_write_zeroes >= bs->bl.request_alignment);
 
     while (bytes > 0 && !ret) {
-        int num = bytes;
+        int64_t num = bytes;
 
         /* Align request.  Block drivers can expect the "bulk" of the request
          * to be aligned, and that unaligned requests do not cross cluster