SYSFS: Allow boot time switching between deprecated and modern sysfs layout

I have some systems which need legacy sysfs due to old tools that are
making assumptions that a directory can never be a symlink to another
directory, and it's a big hazzle to compile separate kernels for them.

This patch turns CONFIG_SYSFS_DEPRECATED into a run time option
that can be switched on/off the kernel command line. This way
the same binary can be used in both cases with just a option
on the command line.

The old CONFIG_SYSFS_DEPRECATED_V2 option is still there to set
the default. I kept the weird name to not break existing
config files.

Also the compat code can be still completely disabled by undefining
CONFIG_SYSFS_DEPRECATED_SWITCH -- just the optimizer takes
care of this now instead of lots of ifdefs. This makes the code
look nicer.

v2: This is an updated version on top of Kay's patch to only
handle the block devices. I tested it on my old systems
and that seems to work.

Cc: axboe@kernel.dk
Signed-off-by: Andi Kleen <ak@linux.intel.com>
Cc: Kay Sievers <kay.sievers@vrfy.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 9 insertions, 10 deletions

diff --git a/fs/partitions/check.c b/fs/partitions/check.c
index 79fbf3f..137bf97 100644
--- a/fs/partitions/check.c
+++ b/fs/partitions/check.c
@@ -513,14 +513,14 @@ void register_disk(struct gendisk *disk)
 
 	if (device_add(ddev))
 		return;
-#ifndef CONFIG_SYSFS_DEPRECATED
-	err = sysfs_create_link(block_depr, &ddev->kobj,
-				kobject_name(&ddev->kobj));
-	if (err) {
-		device_del(ddev);
-		return;
+	if (!sysfs_deprecated) {
+		err = sysfs_create_link(block_depr, &ddev->kobj,
+					kobject_name(&ddev->kobj));
+		if (err) {
+			device_del(ddev);
+			return;
+		}
 	}
-#endif
 	disk->part0.holder_dir = kobject_create_and_add("holders", &ddev->kobj);
 	disk->slave_dir = kobject_create_and_add("slaves", &ddev->kobj);
 
@@ -737,8 +737,7 @@ void del_gendisk(struct gendisk *disk)
 	kobject_put(disk->part0.holder_dir);
 	kobject_put(disk->slave_dir);
 	disk->driverfs_dev = NULL;
-#ifndef CONFIG_SYSFS_DEPRECATED
-	sysfs_remove_link(block_depr, dev_name(disk_to_dev(disk)));
-#endif
+	if (!sysfs_deprecated)
+		sysfs_remove_link(block_depr, dev_name(disk_to_dev(disk)));
 	device_del(disk_to_dev(disk));
 }