block: Allow devices to indicate whether discarded blocks are zeroed
The discard ioctl is used by mkfs utilities to clear a block device
prior to putting metadata down. However, not all devices return zeroed
blocks after a discard. Some drives return stale data, potentially
containing old superblocks. It is therefore important to know whether
discarded blocks are properly zeroed.
Both ATA and SCSI drives have configuration bits that indicate whether
zeroes are returned after a discard operation. Implement a block level
interface that allows this information to be bubbled up the stack and
queried via a new block device ioctl.
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/block/blk-settings.c b/block/blk-settings.c
index 1ebc1fd..dd1f1e0 100644
--- a/block/blk-settings.c
+++ b/block/blk-settings.c
@@ -101,6 +101,7 @@
lim->discard_granularity = 0;
lim->discard_alignment = 0;
lim->discard_misaligned = 0;
+ lim->discard_zeroes_data = -1;
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;
@@ -544,6 +545,7 @@
t->io_min = max(t->io_min, b->io_min);
t->no_cluster |= b->no_cluster;
+ t->discard_zeroes_data &= b->discard_zeroes_data;
/* Bottom device offset aligned? */
if (offset &&
diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index 3147145..8606c95 100644
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c
@@ -136,6 +136,11 @@
return queue_var_show(q->limits.max_discard_sectors << 9, page);
}
+static ssize_t queue_discard_zeroes_data_show(struct request_queue *q, char *page)
+{
+ return queue_var_show(queue_discard_zeroes_data(q), page);
+}
+
static ssize_t
queue_max_sectors_store(struct request_queue *q, const char *page, size_t count)
{
@@ -313,6 +318,11 @@
.show = queue_discard_max_show,
};
+static struct queue_sysfs_entry queue_discard_zeroes_data_entry = {
+ .attr = {.name = "discard_zeroes_data", .mode = S_IRUGO },
+ .show = queue_discard_zeroes_data_show,
+};
+
static struct queue_sysfs_entry queue_nonrot_entry = {
.attr = {.name = "rotational", .mode = S_IRUGO | S_IWUSR },
.show = queue_nonrot_show,
@@ -350,6 +360,7 @@
&queue_io_opt_entry.attr,
&queue_discard_granularity_entry.attr,
&queue_discard_max_entry.attr,
+ &queue_discard_zeroes_data_entry.attr,
&queue_nonrot_entry.attr,
&queue_nomerges_entry.attr,
&queue_rq_affinity_entry.attr,
diff --git a/block/compat_ioctl.c b/block/compat_ioctl.c
index 9bd086c..4eb8e9e 100644
--- a/block/compat_ioctl.c
+++ b/block/compat_ioctl.c
@@ -747,6 +747,8 @@
return compat_put_uint(arg, bdev_io_opt(bdev));
case BLKALIGNOFF:
return compat_put_int(arg, bdev_alignment_offset(bdev));
+ case BLKDISCARDZEROES:
+ return compat_put_uint(arg, bdev_discard_zeroes_data(bdev));
case BLKFLSBUF:
case BLKROSET:
case BLKDISCARD:
diff --git a/block/ioctl.c b/block/ioctl.c
index 1f4d1de..be48ea5 100644
--- a/block/ioctl.c
+++ b/block/ioctl.c
@@ -280,6 +280,8 @@
return put_uint(arg, bdev_io_opt(bdev));
case BLKALIGNOFF:
return put_int(arg, bdev_alignment_offset(bdev));
+ case BLKDISCARDZEROES:
+ return put_uint(arg, bdev_discard_zeroes_data(bdev));
case BLKSECTGET:
return put_ushort(arg, queue_max_sectors(bdev_get_queue(bdev)));
case BLKRASET: