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>
diff --git a/init/Kconfig b/init/Kconfig
index 137609f..d742b6f 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -660,8 +660,12 @@
depends on SYSFS
default n
help
- This option switches the layout of the "block" class devices, to not
- show up in /sys/class/block/, but only in /sys/block/.
+ This option adds code that switches the layout of the "block" class
+ devices, to not show up in /sys/class/block/, but only in
+ /sys/block/.
+
+ This switch is only active when the sysfs.deprecated=1 boot option is
+ passed or the SYSFS_DEPRECATED_V2 option is set.
This option allows new kernels to run on old distributions and tools,
which might get confused by /sys/class/block/. Since 2007/2008 all
@@ -672,8 +676,22 @@
option enabled.
Only if you are using a new kernel on an old distribution, you might
- need to say Y here. Never say Y, if the original kernel, that came
- with your distribution, has not set this option.
+ need to say Y here.
+
+config SYSFS_DEPRECATED_V2
+ bool "enabled deprecated sysfs features by default"
+ default n
+ depends on SYSFS
+ depends on SYSFS_DEPRECATED
+ help
+ Enable deprecated sysfs by default.
+
+ See the CONFIG_SYSFS_DEPRECATED option for more details about this
+ option.
+
+ Only if you are using a new kernel on an old distribution, you might
+ need to say Y here. Even then, odds are you would not need it
+ enabled, you can always pass the boot option if absolutely necessary.
config RELAY
bool "Kernel->user space relay support (formerly relayfs)"