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 1078969889fd..9c63a5687d69 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 6cf9069f3150..f7f906f0a2f2 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));
 }