block: Expose discard granularity

While SSDs track block usage on a per-sector basis, RAID arrays often
have allocation blocks that are bigger.  Allow the discard granularity
and alignment to be set and teach the topology stacking logic how to
handle them.

Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

3 files changed, 70 insertions, 10 deletions

diff --git a/block/blk-settings.c b/block/blk-settings.c
index 66d4aa8799b7..7f986cafacd5 100644
--- a/block/blk-settings.c
+++ b/block/blk-settings.c
@@ -96,7 +96,10 @@ void blk_set_default_limits(struct queue_limits *lim)
         lim->max_segment_size = MAX_SEGMENT_SIZE;
         lim->max_sectors = BLK_DEF_MAX_SECTORS;
         lim->max_hw_sectors = INT_MAX;
-        lim->max_discard_sectors = SAFE_MAX_SECTORS;
+        lim->max_discard_sectors = 0;
+        lim->discard_granularity = 0;
+        lim->discard_alignment = 0;
+        lim->discard_misaligned = 0;
         lim->logical_block_size = lim->physical_block_size = lim->io_min = 512;
         lim->bounce_pfn = (unsigned long)(BLK_BOUNCE_ANY >> PAGE_SHIFT);
         lim->alignment_offset = 0;
@@ -488,6 +491,16 @@ void blk_queue_stack_limits(struct request_queue *t, struct request_queue *b)
 }
 EXPORT_SYMBOL(blk_queue_stack_limits);
 
+static unsigned int lcm(unsigned int a, unsigned int b)
+{
+        if (a && b)
+                return (a * b) / gcd(a, b);
+        else if (b)
+                return b;
+
+        return a;
+}
+
 /**
  * blk_stack_limits - adjust queue_limits for stacked devices
  * @t:  the stacking driver limits (top)
@@ -502,6 +515,10 @@ EXPORT_SYMBOL(blk_queue_stack_limits);
 int blk_stack_limits(struct queue_limits *t, struct queue_limits *b,
                      sector_t offset)
 {
+        int ret;
+
+        ret = 0;
+
         t->max_sectors = min_not_zero(t->max_sectors, b->max_sectors);
         t->max_hw_sectors = min_not_zero(t->max_hw_sectors, b->max_hw_sectors);
         t->bounce_pfn = min_not_zero(t->bounce_pfn, b->bounce_pfn);
@@ -531,7 +548,13 @@ int blk_stack_limits(struct queue_limits *t, struct queue_limits *b,
         if (offset &&
             (offset & (b->physical_block_size - 1)) != b->alignment_offset) {
                 t->misaligned = 1;
-                return -1;
+                ret = -1;
+        }
+
+        if (offset &&
+            (offset & (b->discard_granularity - 1)) != b->discard_alignment) {
+                t->discard_misaligned = 1;
+                ret = -1;
         }
 
         /* If top has no alignment offset, inherit from bottom */
@@ -539,23 +562,26 @@ int blk_stack_limits(struct queue_limits *t, struct queue_limits *b,
                 t->alignment_offset =
                         b->alignment_offset & (b->physical_block_size - 1);
 
+        if (!t->discard_alignment)
+                t->discard_alignment =
+                        b->discard_alignment & (b->discard_granularity - 1);
+
         /* Top device aligned on logical block boundary? */
         if (t->alignment_offset & (t->logical_block_size - 1)) {
                 t->misaligned = 1;
-                return -1;
+                ret = -1;
         }
 
-        /* Find lcm() of optimal I/O size */
-        if (t->io_opt && b->io_opt)
-                t->io_opt = (t->io_opt * b->io_opt) / gcd(t->io_opt, b->io_opt);
-        else if (b->io_opt)
-                t->io_opt = b->io_opt;
+        /* Find lcm() of optimal I/O size and granularity */
+        t->io_opt = lcm(t->io_opt, b->io_opt);
+        t->discard_granularity = lcm(t->discard_granularity,
+                                     b->discard_granularity);
 
         /* Verify that optimal I/O size is a multiple of io_min */
         if (t->io_min && t->io_opt % t->io_min)
-                return -1;
+                ret = -1;
 
-        return 0;
+        return ret;
 }
 EXPORT_SYMBOL(blk_stack_limits);
 
diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index 8a6d81afb284..3147145edc15 100644
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c
@@ -126,6 +126,16 @@ static ssize_t queue_io_opt_show(struct request_queue *q, char *page)
         return queue_var_show(queue_io_opt(q), page);
 }
 
+static ssize_t queue_discard_granularity_show(struct request_queue *q, char *page)
+{
+        return queue_var_show(q->limits.discard_granularity, page);
+}
+
+static ssize_t queue_discard_max_show(struct request_queue *q, char *page)
+{
+        return queue_var_show(q->limits.max_discard_sectors << 9, page);
+}
+
 static ssize_t
 queue_max_sectors_store(struct request_queue *q, const char *page, size_t count)
 {
@@ -293,6 +303,16 @@ static struct queue_sysfs_entry queue_io_opt_entry = {
         .show = queue_io_opt_show,
 };
 
+static struct queue_sysfs_entry queue_discard_granularity_entry = {
+        .attr = {.name = "discard_granularity", .mode = S_IRUGO },
+        .show = queue_discard_granularity_show,
+};
+
+static struct queue_sysfs_entry queue_discard_max_entry = {
+        .attr = {.name = "discard_max_bytes", .mode = S_IRUGO },
+        .show = queue_discard_max_show,
+};
+
 static struct queue_sysfs_entry queue_nonrot_entry = {
         .attr = {.name = "rotational", .mode = S_IRUGO | S_IWUSR },
         .show = queue_nonrot_show,
@@ -328,6 +348,8 @@ static struct attribute *default_attrs[] = {
         &queue_physical_block_size_entry.attr,
         &queue_io_min_entry.attr,
         &queue_io_opt_entry.attr,
+        &queue_discard_granularity_entry.attr,
+        &queue_discard_max_entry.attr,
         &queue_nonrot_entry.attr,
         &queue_nomerges_entry.attr,
         &queue_rq_affinity_entry.attr,
diff --git a/block/genhd.c b/block/genhd.c
index 517e4332cb37..b11a4ad7d571 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -861,12 +861,23 @@ static ssize_t disk_alignment_offset_show(struct device *dev,
         return sprintf(buf, "%d\n", queue_alignment_offset(disk->queue));
 }
 
+static ssize_t disk_discard_alignment_show(struct device *dev,
+                                           struct device_attribute *attr,
+                                           char *buf)
+{
+        struct gendisk *disk = dev_to_disk(dev);
+
+        return sprintf(buf, "%u\n", queue_discard_alignment(disk->queue));
+}
+
 static DEVICE_ATTR(range, S_IRUGO, disk_range_show, NULL);
 static DEVICE_ATTR(ext_range, S_IRUGO, disk_ext_range_show, NULL);
 static DEVICE_ATTR(removable, S_IRUGO, disk_removable_show, NULL);
 static DEVICE_ATTR(ro, S_IRUGO, disk_ro_show, NULL);
 static DEVICE_ATTR(size, S_IRUGO, part_size_show, NULL);
 static DEVICE_ATTR(alignment_offset, S_IRUGO, disk_alignment_offset_show, NULL);
+static DEVICE_ATTR(discard_alignment, S_IRUGO, disk_discard_alignment_show,
+                   NULL);
 static DEVICE_ATTR(capability, S_IRUGO, disk_capability_show, NULL);
 static DEVICE_ATTR(stat, S_IRUGO, part_stat_show, NULL);
 static DEVICE_ATTR(inflight, S_IRUGO, part_inflight_show, NULL);
@@ -887,6 +898,7 @@ static struct attribute *disk_attrs[] = {
         &dev_attr_ro.attr,
         &dev_attr_size.attr,
         &dev_attr_alignment_offset.attr,
+        &dev_attr_discard_alignment.attr,
         &dev_attr_capability.attr,
         &dev_attr_stat.attr,
         &dev_attr_inflight.attr,