Maximum transfer size when accessing a kernel block device is only relevant when using SCSI passthrough (SG_IO ioctl) since only in this case the requests are passed directly to underlying hardware with no pre-processing. Same is true when using /dev/sg* character devices (which only support SG_IO)
Therefore split the block driver's advertized max transfer size by the regular max transfer size, and the max transfer size for SCSI passthrough (the new max_ioctl_transfer field) In the next patch, the qemu block drivers that support SCSI passthrough will set the max_ioctl_transfer field, and simultaneously, the block devices that implement scsi passthrough will switch to 'blk_get_max_ioctl_transfer' to query and to pass it to the guest. Signed-off-by: Maxim Levitsky <mlevi...@redhat.com> --- block/block-backend.c | 12 ++++++++++++ block/io.c | 2 ++ include/block/block_int.h | 4 ++++ include/sysemu/block-backend.h | 1 + 4 files changed, 19 insertions(+) diff --git a/block/block-backend.c b/block/block-backend.c index ce78d30794..c1d149a755 100644 --- a/block/block-backend.c +++ b/block/block-backend.c @@ -1938,6 +1938,18 @@ uint32_t blk_get_max_transfer(BlockBackend *blk) return MIN_NON_ZERO(max, INT_MAX); } +/* Returns the maximum transfer length, for SCSI passthrough */ +uint32_t blk_get_max_ioctl_transfer(BlockBackend *blk) +{ + BlockDriverState *bs = blk_bs(blk); + uint32_t max = 0; + + if (bs) { + max = bs->bl.max_ioctl_transfer; + } + return MIN_NON_ZERO(max, INT_MAX); +} + int blk_get_max_iov(BlockBackend *blk) { return blk->root->bs->bl.max_iov; diff --git a/block/io.c b/block/io.c index ec5e152bb7..3eae176992 100644 --- a/block/io.c +++ b/block/io.c @@ -126,6 +126,8 @@ static void bdrv_merge_limits(BlockLimits *dst, const BlockLimits *src) { dst->opt_transfer = MAX(dst->opt_transfer, src->opt_transfer); dst->max_transfer = MIN_NON_ZERO(dst->max_transfer, src->max_transfer); + dst->max_ioctl_transfer = MIN_NON_ZERO(dst->max_ioctl_transfer, + src->max_ioctl_transfer); dst->opt_mem_alignment = MAX(dst->opt_mem_alignment, src->opt_mem_alignment); dst->min_mem_alignment = MAX(dst->min_mem_alignment, diff --git a/include/block/block_int.h b/include/block/block_int.h index 95d9333be1..e9874c8c23 100644 --- a/include/block/block_int.h +++ b/include/block/block_int.h @@ -678,6 +678,10 @@ typedef struct BlockLimits { * clamped down. */ uint32_t max_transfer; + /* Maximal transfer length for SCSI passthrough (ioctl interface) */ + uint32_t max_ioctl_transfer; + + /* memory alignment, in bytes so that no bounce buffer is needed */ size_t min_mem_alignment; diff --git a/include/sysemu/block-backend.h b/include/sysemu/block-backend.h index 8203d7f6f9..b019a37b7a 100644 --- a/include/sysemu/block-backend.h +++ b/include/sysemu/block-backend.h @@ -203,6 +203,7 @@ void blk_eject(BlockBackend *blk, bool eject_flag); int blk_get_flags(BlockBackend *blk); uint32_t blk_get_request_alignment(BlockBackend *blk); uint32_t blk_get_max_transfer(BlockBackend *blk); +uint32_t blk_get_max_ioctl_transfer(BlockBackend *blk); int blk_get_max_iov(BlockBackend *blk); void blk_set_guest_block_size(BlockBackend *blk, int align); void *blk_try_blockalign(BlockBackend *blk, size_t size); -- 2.26.2