[PATCH] sysctl: Undeprecate sys_sysctl

The basic issue is that despite have been deprecated and warned about as a
very bad thing in the man pages since its inception there are a few real
users of sys_sysctl. It was my assumption that because sysctl had been
deprecated for all of 2.6 there would be no user space users by this point,
so I initially gave sys_sysctl a very short deprecation period.

Now that I know there are a few real users the only sane way to proceed
with deprecation is to push the time limit out to a year or two work and
work with distributions that have big testing pools like fedora core to
find these last remaining users.

Which means that the sys_sysctl interface needs to be maintained in the
meantime.

Since I have provided a technical measure that allows us to add new sysctl
entries without reserving more binary numbers I believe that is enough to
fix the sys_sysctl binary interface maintenance problems, because there is
no longer a need to change the binary interface at all.

Since the sys_sysctl implementation needs to stay around for a while and
the worst of the maintenance issues that caused us to occasionally break
the ABI have been addressed I don't see any advantage in continuing with
the removal of sys_sysctl.

So instead of merely increasing the deprecation period this patch removes
the deprecation of sys_sysctl and modifies the kernel to compile the code
in by default.

With committing to maintain sys_sysctl we get all of the advantages of a
fast interface for anything that needs it. Currently sys_sysctl is about
5x faster than /proc/sys, for the same string data.

Signed-off-by: Eric W. Biederman <[e-mail]>
Acked-by: Alan Cox <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

Documentation/feature-removal-schedule.txt

···
 
 ---------------------------
 
-What:	sys_sysctl
-When:	January 2007
-Why:	The same information is available through /proc/sys and that is the
-	interface user space prefers to use. And there do not appear to be
-	any existing user in user space of sys_sysctl.  The additional
-	maintenance overhead of keeping a set of binary names gets
-	in the way of doing a good job of maintaining this interface.
-
-Who:	Eric Biederman <[e-mail]>
-
----------------------------
-
 What:	PCMCIA control ioctl (needed for pcmcia-cs [cardmgr, cardctl])
 When:	November 2005
 Files:	drivers/pcmcia/: pcmcia_ioctl.c

init/Kconfig

···
 
 config SYSCTL_SYSCALL
 	bool "Sysctl syscall support" if EMBEDDED
-	default n
+	default y
 	select SYSCTL
 	---help---
-	  Enable the deprecated sysctl system call.  sys_sysctl uses
-	  binary paths that have been found to be a major pain to maintain
-	  and use.  The interface in /proc/sys is now the primary and what
-	  everyone uses.
+	  sys_sysctl uses binary paths that have been found challenging
+	  to properly maintain and use.  The interface in /proc/sys
+	  using paths with ascii names is now the primary path to this
+	  information.
 
-	  Nothing has been using the binary sysctl interface for some
-	  time now so nothing should break if you disable sysctl syscall
-	  support, and your kernel will get marginally smaller.
+	  Almost nothing using the binary sysctl interface so if you are
+	  trying to save some space it is probably safe to disable this,
+	  making your kernel marginally smaller.
 
-	  Unless you have an application that uses the sys_sysctl interface
- 	  you should probably say N here.
+	  If unsure say Y here.
 
 config KALLSYMS
 	 bool "Load all symbols for debugging/kksymoops" if EMBEDDED