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Subject[PATCH v4 4/5] block: export diskseq in sysfs
Date
From: Matteo Croce <mcroce@microsoft.com>

Add a new sysfs handle to export the new diskseq value.
Place it in <sysfs>/block/<disk>/diskseq and document it.

$ grep . /sys/class/block/*/diskseq
/sys/class/block/loop0/diskseq:13
/sys/class/block/loop1/diskseq:14
/sys/class/block/loop2/diskseq:5
/sys/class/block/loop3/diskseq:6
/sys/class/block/ram0/diskseq:1
/sys/class/block/ram1/diskseq:2
/sys/class/block/vda/diskseq:7

Signed-off-by: Matteo Croce <mcroce@microsoft.com>
---
Documentation/ABI/testing/sysfs-block | 12 ++++++++++++
block/genhd.c | 10 ++++++++++
2 files changed, 22 insertions(+)

diff --git a/Documentation/ABI/testing/sysfs-block b/Documentation/ABI/testing/sysfs-block
index e34cdeeeb9d4..a0ed87386639 100644
--- a/Documentation/ABI/testing/sysfs-block
+++ b/Documentation/ABI/testing/sysfs-block
@@ -28,6 +28,18 @@ Description:
For more details refer Documentation/admin-guide/iostats.rst


+What: /sys/block/<disk>/diskseq
+Date: February 2021
+Contact: Matteo Croce <mcroce@microsoft.com>
+Description:
+ The /sys/block/<disk>/diskseq files reports the disk
+ sequence number, which is a monotonically increasing
+ number assigned to every drive.
+ Some devices, like the loop device, refresh such number
+ every time the backing file is changed.
+ The value type is 64 bit unsigned.
+
+
What: /sys/block/<disk>/<part>/stat
Date: February 2008
Contact: Jerome Marchand <jmarchan@redhat.com>
diff --git a/block/genhd.c b/block/genhd.c
index 3d9c9d189ff7..422c0dbc6ce2 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -985,6 +985,14 @@ static ssize_t disk_discard_alignment_show(struct device *dev,
return sprintf(buf, "%d\n", queue_discard_alignment(disk->queue));
}

+static ssize_t diskseq_show(struct device *dev,
+ struct device_attribute *attr, char *buf)
+{
+ struct gendisk *disk = dev_to_disk(dev);
+
+ return sprintf(buf, "%llu\n", disk->diskseq);
+}
+
static DEVICE_ATTR(range, 0444, disk_range_show, NULL);
static DEVICE_ATTR(ext_range, 0444, disk_ext_range_show, NULL);
static DEVICE_ATTR(removable, 0444, disk_removable_show, NULL);
@@ -997,6 +1005,7 @@ static DEVICE_ATTR(capability, 0444, disk_capability_show, NULL);
static DEVICE_ATTR(stat, 0444, part_stat_show, NULL);
static DEVICE_ATTR(inflight, 0444, part_inflight_show, NULL);
static DEVICE_ATTR(badblocks, 0644, disk_badblocks_show, disk_badblocks_store);
+static DEVICE_ATTR(diskseq, 0444, diskseq_show, NULL);

#ifdef CONFIG_FAIL_MAKE_REQUEST
ssize_t part_fail_show(struct device *dev,
@@ -1042,6 +1051,7 @@ static struct attribute *disk_attrs[] = {
&dev_attr_events.attr,
&dev_attr_events_async.attr,
&dev_attr_events_poll_msecs.attr,
+ &dev_attr_diskseq.attr,
#ifdef CONFIG_FAIL_MAKE_REQUEST
&dev_attr_fail.attr,
#endif
--
2.31.1
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