[RFC PATCH 1/5] block/genhd: Notify udev about capacity change

[Balbir Singh <sblbir@amazon.com>]

Allow block/genhd to notify user space (via udev) about disk size changes
using a new helper disk_set_capacity(), which is a wrapper on top
of set_capacity(). disk_set_capacity() will only notify via udev if
the current capacity or the target capacity is not zero.

Background:

As a part of a patch to allow sending the RESIZE event on disk capacity
change, Christoph (hch@lst.de) requested that the patch be made generic
and the hacks for virtio block and xen block devices be removed and
merged via a generic helper.

Testing:
1. I did some basic testing with an NVME device, by resizing it in
the backend and ensured that udevd received the event.

Suggested-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Balbir Singh <sblbir@amazon.com>
Signed-off-by: Someswarudu Sangaraju <ssomesh@amazon.com>
Signed-off-by: Balbir Singh <sblbir@amazon.com>
---
 block/genhd.c         | 19 +++++++++++++++++++
 include/linux/genhd.h |  1 +
 2 files changed, 20 insertions(+)

diff --git a/block/genhd.c b/block/genhd.c
index ff6268970ddc..94faec98607b 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -46,6 +46,25 @@ static void disk_add_events(struct gendisk *disk);
 static void disk_del_events(struct gendisk *disk);
 static void disk_release_events(struct gendisk *disk);
 
+/*
+ * Set disk capacity and notify if the size is not currently
+ * zero and will not be set to zero
+ */
+void disk_set_capacity(struct gendisk *disk, sector_t size)
+{
+	sector_t capacity = get_capacity(disk);
+
+	set_capacity(disk, size);
+	if (capacity != 0 && size != 0) {
+		char *envp[] = { "RESIZE=1", NULL };
+
+		kobject_uevent_env(&disk_to_dev(disk)->kobj, KOBJ_CHANGE, envp);
+	}
+}
+
+EXPORT_SYMBOL_GPL(disk_set_capacity);
+
+
 void part_inc_in_flight(struct request_queue *q, struct hd_struct *part, int rw)
 {
 	if (queue_is_mq(q))
diff --git a/include/linux/genhd.h b/include/linux/genhd.h
index a927829bb73a..f1a5ddcc781d 100644
--- a/include/linux/genhd.h
+++ b/include/linux/genhd.h
@@ -449,6 +449,7 @@ static inline int get_disk_ro(struct gendisk *disk)
 extern void disk_block_events(struct gendisk *disk);
 extern void disk_unblock_events(struct gendisk *disk);
 extern void disk_flush_events(struct gendisk *disk, unsigned int mask);
+extern void disk_set_capacity(struct gendisk *disk, sector_t size);
 extern unsigned int disk_clear_events(struct gendisk *disk, unsigned int mask);
 
 /* drivers/char/random.c */
-- 
2.16.5


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