[RESEND x2][PATCH v2] block: partition: Add partition specific uevent callbacks for partition info

[John Stultz <john.stultz@linaro.org>]

From: San Mehat <san@google.com>

This patch has been carried in the Android tree for quite some
time and is one of the few patches required to get a mainline
kernel up and running with an exsiting Android userspace. So I
wanted to submit it for review and consideration if it should
be merged.

For partitions, add new uevent parameters 'PARTN' which
specifies the partitions index in the table, and 'PARTNAME',
which specifies PARTNAME specifices the partition name of a
partition device.

Android's userspace uses this for creating device node links from the
partition name and number: ie:
	/dev/block/platform/soc/by-name/system
or
	/dev/block/platform/soc/by-num/p1

One can see its usage here:
https://android.googlesource.com/platform/system/core/+/master/init/devices.cpp#355
and
https://android.googlesource.com/platform/system/core/+/master/init/devices.cpp#494

Cc: Jens Axboe <axboe@kernel.dk>
Cc: Rom Lemarchand <romlem@google.com>
Cc: Android Kernel Team <kernel-team@android.com>
Cc: Jeff Moyer <jmoyer@redhat.com>
Cc: harald@redhat.com
Cc: Kees Cook <keescook@chromium.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Kay Sievers <kay@vrfy.org>
Signed-off-by: Dima Zavin <dima@android.com>
[Dropped NPARTS and reworded commit message for context]
Signed-off-by: John Stultz <john.stultz@linaro.org>
---
v2: Dropped NPARTS thanks to Jeff noticing it wasn't used

 block/partition-generic.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/block/partition-generic.c b/block/partition-generic.c
index 746935a..ae95e96 100644
--- a/block/partition-generic.c
+++ b/block/partition-generic.c
@@ -216,10 +216,21 @@ static void part_release(struct device *dev)
 	kfree(p);
 }
 
+static int part_uevent(struct device *dev, struct kobj_uevent_env *env)
+{
+	struct hd_struct *part = dev_to_part(dev);
+
+	add_uevent_var(env, "PARTN=%u", part->partno);
+	if (part->info && part->info->volname[0])
+		add_uevent_var(env, "PARTNAME=%s", part->info->volname);
+	return 0;
+}
+
 struct device_type part_type = {
 	.name		= "partition",
 	.groups		= part_attr_groups,
 	.release	= part_release,
+	.uevent		= part_uevent,
 };
 
 static void delete_partition_rcu_cb(struct rcu_head *head)
-- 
1.9.1