diff options
authorAndrew Morton <>2007-07-15 23:41:20 -0700
committerLinus Torvalds <>2007-07-16 09:05:49 -0700
commit97d8f83cb734525f96992fd61e4f7323ab3d549c (patch)
parent36cf3b5c3b7228bcf5124c530d50080b61a59f69 (diff)
Add Documentation/sysctl/ctl_unnumbered.txt
Poeple keep on adding new numbered sysctls, when they're supposed not to. Add a documentation file which explain why new sysctls should use CTL_UNNUMBERED. The next patch will sprinkle pointers to this throughout sysctl.c. Eric provided the text (thanks) Cc: "Eric W. Biederman" <> Signed-off-by: Andrew Morton <> Signed-off-by: Linus Torvalds <>
1 files changed, 22 insertions, 0 deletions
diff --git a/Documentation/sysctl/ctl_unnumbered.txt b/Documentation/sysctl/ctl_unnumbered.txt
new file mode 100644
index 000000000000..23003a8ea3e7
--- /dev/null
+++ b/Documentation/sysctl/ctl_unnumbered.txt
@@ -0,0 +1,22 @@
+Except for a few extremely rare exceptions user space applications do not use
+the binary sysctl interface. Instead everyone uses /proc/sys/... with
+readable ascii names.
+Recently the kernel has started supporting setting the binary sysctl value to
+CTL_UNNUMBERED so we no longer need to assign a binary sysctl path to allow
+sysctls to show up in /proc/sys.
+Assigning binary sysctl numbers is an endless source of conflicts in sysctl.h,
+breaking of the user space ABI (because of those conflicts), and maintenance
+problems. A complete pass through all of the sysctl users revealed multiple
+instances where the sysctl binary interface was broken and had gone undetected
+for years.
+So please do not add new binary sysctl numbers. They are unneeded and
+If you really need a new binary sysctl number please first merge your sysctl
+into the kernel and then as a separate patch allocate a binary sysctl number.
+(, June 2007)