sysctl: deprecate sys_sysctl in a user space visible fashion.

After adding checking to register_sysctl_table and finding a whole new set
of bugs.  Missed by countless code reviews and testers I have finally lost
patience with the binary sysctl interface.

The binary sysctl interface has been sort of deprecated for years and
finding a user space program that uses the syscall is more difficult then
finding a needle in a haystack.  Problems continue to crop up, with the in
kernel implementation.  So since supporting something that no one uses is
silly, deprecate sys_sysctl with a sufficient grace period and notice that
the handful of user space applications that care can be fixed or replaced.

The /proc/sys sysctl interface that people use will continue to be
supported indefinitely.

This patch moves the tested warning about sysctls from the path where
sys_sysctl to a separate path called from both implementations of
sys_sysctl, and it adds a proper entry into
Documentation/feature-removal-schedule.

Allowing us to revisit this in a couple years time and actually kill
sys_sysctl.

[lethal@linux-sh.org: sysctl: Fix syscall disabled build]
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 35 insertions, 0 deletions

diff --git a/Documentation/feature-removal-schedule.txt b/Documentation/feature-removal-schedule.txt
index 280ec06573e..5b25162cd9a 100644
--- a/Documentation/feature-removal-schedule.txt
+++ b/Documentation/feature-removal-schedule.txt
@@ -82,6 +82,41 @@ Who:	Dominik Brodowski <linux@brodo.de>
 
 ---------------------------
 
+What:	sys_sysctl
+When:	September 2010
+Option: CONFIG_SYSCTL_SYSCALL
+Why:	The same information is available in a more convenient from
+	/proc/sys, and none of the sysctl variables appear to be
+	important performance wise.
+
+	Binary sysctls are a long standing source of subtle kernel
+	bugs and security issues.
+
+	When I looked several months ago all I could find after
+	searching several distributions were 5 user space programs and
+	glibc (which falls back to /proc/sys) using this syscall.
+
+	The man page for sysctl(2) documents it as unusable for user
+	space programs.
+
+	sysctl(2) is not generally ABI compatible to a 32bit user
+	space application on a 64bit and a 32bit kernel.
+
+	For the last several months the policy has been no new binary
+	sysctls and no one has put forward an argument to use them.
+
+	Binary sysctls issues seem to keep happening appearing so
+	properly deprecating them (with a warning to user space) and a
+	2 year grace warning period will mean eventually we can kill
+	them and end the pain.
+
+	In the mean time individual binary sysctls can be dealt with
+	in a piecewise fashion.
+
+Who:	Eric Biederman <ebiederm@xmission.com>
+
+---------------------------
+
 What:  a.out interpreter support for ELF executables
 When:  2.6.25
 Files: fs/binfmt_elf.c