On Tuesday May 8, agk@xxxxxxxxxx wrote:
> From: Neil Brown <neilb@xxxxxxx>
>
> Make sure dm honours max_hw_sectors of underlying devices
I think I want to un-ack this patch (if that makes sense).
I don't think max_hw_sectors is at all relevant to dm or md.
I looked back at the mail thread that sparked this. Someone reported
a problem. I suggested this patch based on differences between
combine_restrictions_low and blk_queue_stack_limits, and we never
heard anything more.
As far as I can tell, max_hw_sectors is only used by bio_add_pc_page
which is only used for the scsi SG_IO ioctl. i.e. it is only needed
when bypassing the block layer and talking very directly to a low
level device.
(Did I get that right Jens?)
So I'm sure this patch doesn't fix the original problem, and I don't
think we really want this patch (it won't hurt, except that it might
confuse readers). We should probably remove
t->max_hw_sectors = min_not_zero(t->max_hw_sectors,b->max_hw_sectors);
from blk_queue_stack_limits.
NeilBrown
>
> Signed-off-by: Neil Brown <neilb@xxxxxxx>
> Signed-off-by: Alasdair G Kergon <agk@xxxxxxxxxx>
> ---
>
> ### Diffstat output
> drivers/md/dm-table.c | 9 +++++++++
> include/linux/device-mapper.h | 1 +
> 2 files changed, 10 insertions(+)
>
> Index: linux-2.6.21/drivers/md/dm-table.c
> ===================================================================
> --- linux-2.6.21.orig/drivers/md/dm-table.c 2007-05-01 17:38:32.000000000 +0100
> +++ linux-2.6.21/drivers/md/dm-table.c 2007-05-01 17:40:45.000000000 +0100
> @@ -99,6 +99,9 @@ static void combine_restrictions_low(str
> lhs->max_segment_size =
> min_not_zero(lhs->max_segment_size, rhs->max_segment_size);
>
> + lhs->max_hw_sectors =
> + min_not_zero(lhs->max_hw_sectors, rhs->max_hw_sectors);
> +
> lhs->seg_boundary_mask =
> min_not_zero(lhs->seg_boundary_mask, rhs->seg_boundary_mask);
>
> @@ -561,6 +564,9 @@ void dm_set_device_limits(struct dm_targ
> rs->max_segment_size =
> min_not_zero(rs->max_segment_size, q->max_segment_size);
>
> + rs->max_hw_sectors =
> + min_not_zero(rs->max_hw_sectors, q->max_hw_sectors);
> +
> rs->seg_boundary_mask =
> min_not_zero(rs->seg_boundary_mask,
> q->seg_boundary_mask);
> @@ -696,6 +702,8 @@ static void check_for_valid_limits(struc
> {
> if (!rs->max_sectors)
> rs->max_sectors = SAFE_MAX_SECTORS;
> + if (!rs->max_hw_sectors)
> + rs->max_hw_sectors = SAFE_MAX_SECTORS;
> if (!rs->max_phys_segments)
> rs->max_phys_segments = MAX_PHYS_SEGMENTS;
> if (!rs->max_hw_segments)
> @@ -889,6 +897,7 @@ void dm_table_set_restrictions(struct dm
> q->max_hw_segments = t->limits.max_hw_segments;
> q->hardsect_size = t->limits.hardsect_size;
> q->max_segment_size = t->limits.max_segment_size;
> + q->max_hw_sectors = t->limits.max_hw_sectors;
> q->seg_boundary_mask = t->limits.seg_boundary_mask;
> if (t->limits.no_cluster)
> q->queue_flags &= ~(1 << QUEUE_FLAG_CLUSTER);
> Index: linux-2.6.21/include/linux/device-mapper.h
> ===================================================================
> --- linux-2.6.21.orig/include/linux/device-mapper.h 2007-05-01 17:38:32.000000000 +0100
> +++ linux-2.6.21/include/linux/device-mapper.h 2007-05-01 17:40:45.000000000 +0100
> @@ -115,6 +115,7 @@ struct io_restrictions {
> unsigned short max_hw_segments;
> unsigned short hardsect_size;
> unsigned int max_segment_size;
> + unsigned int max_hw_sectors;
> unsigned long seg_boundary_mask;
> unsigned char no_cluster; /* inverted so that 0 is default */
> };
--
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