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>

2 files changed, 19 insertions, 11 deletions

diff --git a/drivers/base/class.c b/drivers/base/class.c
index 1078969..9c63a56 100644
--- a/drivers/base/class.c
+++ b/drivers/base/class.c
@@ -184,9 +184,9 @@ int __class_register(struct class *cls, struct lock_class_key *key)
 	if (!cls->dev_kobj)
 		cls->dev_kobj = sysfs_dev_char_kobj;
 
-#if defined(CONFIG_SYSFS_DEPRECATED) && defined(CONFIG_BLOCK)
+#if defined(CONFIG_BLOCK)
 	/* let the block class directory show up in the root of sysfs */
-	if (cls != &block_class)
+	if (!sysfs_deprecated || cls != &block_class)
 		cp->class_subsys.kobj.kset = class_kset;
 #else
 	cp->class_subsys.kobj.kset = class_kset;
diff --git a/drivers/base/core.c b/drivers/base/core.c
index 6cf9069..f7f906f 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -26,6 +26,19 @@
 #include "base.h"
 #include "power/power.h"
 
+#ifdef CONFIG_SYSFS_DEPRECATED
+#ifdef CONFIG_SYSFS_DEPRECATED_V2
+long sysfs_deprecated = 1;
+#else
+long sysfs_deprecated = 0;
+#endif
+static __init int sysfs_deprecated_setup(char *arg)
+{
+	return strict_strtol(arg, 10, &sysfs_deprecated);
+}
+early_param("sysfs.deprecated", sysfs_deprecated_setup);
+#endif
+
 int (*platform_notify)(struct device *dev) = NULL;
 int (*platform_notify_remove)(struct device *dev) = NULL;
 static struct kobject *dev_kobj;
@@ -617,14 +630,13 @@ static struct kobject *get_device_parent(struct device *dev,
 		struct kobject *parent_kobj;
 		struct kobject *k;
 
-#ifdef CONFIG_SYSFS_DEPRECATED
 		/* block disks show up in /sys/block */
-		if (dev->class == &block_class) {
+		if (sysfs_deprecated && dev->class == &block_class) {
 			if (parent && parent->class == &block_class)
 				return &parent->kobj;
 			return &block_class.p->class_subsys.kobj;
 		}
-#endif
+
 		/*
 		 * If we have no parent, we live in "virtual".
 		 * Class-devices with a non class-device as parent, live
@@ -707,11 +719,9 @@ static int device_add_class_symlinks(struct device *dev)
 			goto out_subsys;
 	}
 
-#ifdef CONFIG_SYSFS_DEPRECATED
 	/* /sys/block has directories and does not need symlinks */
-	if (dev->class == &block_class)
+	if (sysfs_deprecated && dev->class == &block_class)
 		return 0;
-#endif
 
 	/* link in the class directory pointing to the device */
 	error = sysfs_create_link(&dev->class->p->class_subsys.kobj,
@@ -738,10 +748,8 @@ static void device_remove_class_symlinks(struct device *dev)
 	if (dev->parent && device_is_not_partition(dev))
 		sysfs_remove_link(&dev->kobj, "device");
 	sysfs_remove_link(&dev->kobj, "subsystem");
-#ifdef CONFIG_SYSFS_DEPRECATED
-	if (dev->class == &block_class)
+	if (sysfs_deprecated && dev->class == &block_class)
 		return;
-#endif
 	sysfs_delete_link(&dev->class->p->class_subsys.kobj, &dev->kobj, dev_name(dev));
 }