| Message ID | 20201217165612.942849-4-mlevitsk@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | SCSI: fix transfer limits for SCSI passthrough | expand |
On 17.12.20 17:56, Maxim Levitsky wrote: > 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. So by “with no pre-processing” you mean in particular no pre-processing by the kernel? I.e., that file-posix for non-SG devices actually has no max transfer limit, because the kernel will split overly long requests by itself? > 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 <mlevitsk@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 24205f5168..ac5aea435e 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); I’d prefer this to be aligned to the opening parenthesis. > 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 1eeafc118c..c59b0aefc4 100644 > --- a/include/block/block_int.h > +++ b/include/block/block_int.h > @@ -686,6 +686,10 @@ typedef struct BlockLimits { > * clamped down. */ > uint32_t max_transfer; > > + /* Maximal transfer length for SCSI passthrough (ioctl interface) */ > + uint32_t max_ioctl_transfer; > + > + Is there a specific reason you added a double newline here? (All other fields in this struct are separated by a single newline) Max > /* 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); >
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 24205f5168..ac5aea435e 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 1eeafc118c..c59b0aefc4 100644 --- a/include/block/block_int.h +++ b/include/block/block_int.h @@ -686,6 +686,10 @@ 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);
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 <mlevitsk@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(+)