From c0ebe9729d1d3e56b17da39e9d42c9edf52dbcdf Mon Sep 17 00:00:00 2001
From: Coly Li <colyli@suse.de>
Date: Tue, 18 Dec 2018 21:49:57 +0800
Subject: [PATCH 1/2] bcache: export backing_dev_name via sysfs
Patch-mainline: Not yet, will submit to upstream for v4.21
References: fate#325346

This patch export dc->backing_dev_name to sysfs file
/sys/block/bcache<?>/bcache/backing_dev_name, then people or user space
tools may know the backing device name of this bcache device.

Of cause it can be done by parsing sysfs links, but this method can be
much simpler to find the link between bcache device and backing device.

Signed-off-by: Coly Li <colyli@suse.de>
---
 drivers/md/bcache/sysfs.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/md/bcache/sysfs.c b/drivers/md/bcache/sysfs.c
index 26f035a0c5b9..8f7674d199fb 100644
--- a/drivers/md/bcache/sysfs.c
+++ b/drivers/md/bcache/sysfs.c
@@ -67,6 +67,7 @@ read_attribute(written);
 read_attribute(btree_written);
 read_attribute(metadata_written);
 read_attribute(active_journal_entries);
+read_attribute(backing_dev_name);
 
 sysfs_time_stats_attribute(btree_gc,	sec, ms);
 sysfs_time_stats_attribute(btree_split, sec, us);
@@ -240,6 +241,12 @@ SHOW(__bch_cached_dev)
 		return strlen(buf);
 	}
 
+	if (attr == &sysfs_backing_dev_name) {
+		snprintf(buf, BDEVNAME_SIZE + 1, "%s", dc->backing_dev_name);
+		strcat(buf, "\n");
+		return strlen(buf);
+	}
+
 #undef var
 	return 0;
 }
@@ -431,6 +438,7 @@ static struct attribute *bch_cached_dev_files[] = {
 	&sysfs_verify,
 	&sysfs_bypass_torture_test,
 #endif
+	&sysfs_backing_dev_name,
 	NULL
 };
 KTYPE(bch_cached_dev);
-- 
2.16.4