pstore: Create a convenient mount point for pstore

Using /dev/pstore as a mount point for the pstore filesystem is slightly
awkward. We don't normally mount filesystems in /dev/ and the /dev/pstore
file isn't created automatically by anything. While this method will
still work, we can create a persistent mount point in sysfs. This will
put pstore on par with things like cgroups and efivarfs.

Signed-off-by: Josh Boyer <[e-mail]>
Acked-by: Kees Cook <[e-mail]>
Signed-off-by: Tony Luck <[e-mail]>

Documentation/ABI/testing/pstore

···
-Where:		/dev/pstore/...
+Where:		/sys/fs/pstore/... (or /dev/pstore/...)
 Date:		March 2011
 Kernel Version: 2.6.39
 Contact:	[e-mail]
···
 		of the console log is captured, but other interesting
 		data can also be saved.
 
-		# mount -t pstore -o kmsg_bytes=8000 - /dev/pstore
+		# mount -t pstore -o kmsg_bytes=8000 - /sys/fs/pstore
 
-		$ ls -l /dev/pstore
+		$ ls -l /sys/fs/pstore/
 		total 0
 		-r--r--r-- 1 root root 7896 Nov 30 15:38 dmesg-erst-1
 
···
 		the file will signal to the underlying persistent storage
 		device that it can reclaim the space for later re-use.
 
-		$ rm /dev/pstore/dmesg-erst-1
+		$ rm /sys/fs/pstore/dmesg-erst-1
 
-		The expectation is that all files in /dev/pstore
+		The expectation is that all files in /sys/fs/pstore/
 		will be saved elsewhere and erased from persistent store
 		soon after boot to free up space ready for the next
 		catastrophe.

fs/pstore/inode.c

···
 	.kill_sb	= pstore_kill_sb,
 };
 
+static struct kobject *pstore_kobj;
+
 static int __init init_pstore_fs(void)
 {
-	return register_filesystem(&pstore_fs_type);
+	int err = 0;
+
+	/* Create a convenient mount point for people to access pstore */
+	pstore_kobj = kobject_create_and_add("pstore", fs_kobj);
+	if (!pstore_kobj) {
+		err = -ENOMEM;
+		goto out;
+	}
+
+	err = register_filesystem(&pstore_fs_type);
+	if (err < 0)
+		kobject_put(pstore_kobj);
+
+out:
+	return err;
 }
 module_init(init_pstore_fs)