diff options
Diffstat (limited to 'block')
| -rw-r--r-- | block/nbd.c | 19 |
1 files changed, 18 insertions, 1 deletions
diff --git a/block/nbd.c b/block/nbd.c index 2e72df528a..208be59602 100644 --- a/block/nbd.c +++ b/block/nbd.c @@ -437,7 +437,24 @@ static void nbd_refresh_limits(BlockDriverState *bs, Error **errp) uint32_t min = s->info.min_block; uint32_t max = MIN_NON_ZERO(NBD_MAX_BUFFER_SIZE, s->info.max_block); - bs->bl.request_alignment = min ? min : BDRV_SECTOR_SIZE; + /* + * If the server did not advertise an alignment: + * - a size that is not sector-aligned implies that an alignment + * of 1 can be used to access those tail bytes + * - advertisement of block status requires an alignment of 1, so + * that we don't violate block layer constraints that block + * status is always aligned (as we can't control whether the + * server will report sub-sector extents, such as a hole at EOF + * on an unaligned POSIX file) + * - otherwise, assume the server is so old that we are safer avoiding + * sub-sector requests + */ + if (!min) { + min = (!QEMU_IS_ALIGNED(s->info.size, BDRV_SECTOR_SIZE) || + s->info.base_allocation) ? 1 : BDRV_SECTOR_SIZE; + } + + bs->bl.request_alignment = min; bs->bl.max_pdiscard = max; bs->bl.max_pwrite_zeroes = max; bs->bl.max_transfer = max; |