On 10/17/24 9:09 AM, Keith Busch wrote:
Drivers with hardware that support write hints need a way to export how
many are available so applications can generically query this.
Something is missing from this patch, namely a change for the SCSI disk
(sd) driver that sets max_write_hints to sdkp->permanent_stream_count.
+What: /sys/block/<disk>/queue/max_write_hints
+Date: October 2024
+Contact: linux-block@xxxxxxxxxxxxxxx
+Description:
+ [RO] Maximum number of write hints supported, 0 if not
+ supported. If supported, valid values are 1 through
+ max_write_hints, inclusive.
That's a bit short. I think it would help to add a reference to the
aspects of the standards related to this attribute: permanent streams
for SCSI and FDP for NVMe.
diff --git a/block/blk-settings.c b/block/blk-settings.c
index a446654ddee5e..921fb4d334fa4 100644
--- a/block/blk-settings.c
+++ b/block/blk-settings.c
@@ -43,6 +43,7 @@ void blk_set_stacking_limits(struct queue_limits *lim)
lim->seg_boundary_mask = BLK_SEG_BOUNDARY_MASK;
/* Inherit limits from component devices */
+ lim->max_write_hints = USHRT_MAX;
lim->max_segments = USHRT_MAX;
lim->max_discard_segments = USHRT_MAX;
lim->max_hw_sectors = UINT_MAX;
@@ -544,6 +545,8 @@ int blk_stack_limits(struct queue_limits *t, struct queue_limits *b,
t->max_segment_size = min_not_zero(t->max_segment_size,
b->max_segment_size);
+ t->max_write_hints = min(t->max_write_hints, b->max_write_hints);
+
alignment = queue_limit_alignment_offset(b, start);
I prefer that lim->max_write_hints is initialized to zero in
blk_set_stacking_limits() and that blk_stack_limits() uses
min_not_zero().
Thanks,
Bart.
