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authorEric W. Biederman <ebiederm@xmission.com>2006-11-05 23:52:12 -0800
committerLinus Torvalds <torvalds@g5.osdl.org>2006-11-06 01:46:23 -0800
commitd99f160ac53e51090f015a8f0617cea25f81a191 (patch)
treea78f1169a937d211e8a02703e1e4ed9cc0edbef8
parent0e009be8a0c2309f3696df70f72ef0075aa34c9c (diff)
downloadlinux-2.6.34-ux500-d99f160ac53e51090f015a8f0617cea25f81a191.tar.gz
[PATCH] sysctl: allow a zero ctl_name in the middle of a sysctl table
Since it is becoming clear that there are just enough users of the binary sysctl interface that completely removing the binary interface from the kernel will not be an option for foreseeable future, we need to find a way to address the sysctl maintenance issues. The basic problem is that sysctl requires one central authority to allocate sysctl numbers, or else conflicts and ABI breakage occur. The proc interface to sysctl does not have that problem, as names are not densely allocated. By not terminating a sysctl table until I have neither a ctl_name nor a procname, it becomes simple to add sysctl entries that don't show up in the binary sysctl interface. Which allows people to avoid allocating a binary sysctl value when not needed. I have audited the kernel code and in my reading I have not found a single sysctl table that wasn't terminated by a completely zero filled entry. So this change in behavior should not affect anything. I think this mechanism eases the pain enough that combined with a little disciple we can solve the reoccurring sysctl ABI breakage. Signed-off-by: Eric W. Biederman <ebiederm@xmission.com> Acked-by: Alan Cox <alan@redhat.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
-rw-r--r--include/linux/sysctl.h9
-rw-r--r--kernel/sysctl.c8
2 files changed, 11 insertions, 6 deletions
diff --git a/include/linux/sysctl.h b/include/linux/sysctl.h
index 1b24bd45e08..c184732a70f 100644
--- a/include/linux/sysctl.h
+++ b/include/linux/sysctl.h
@@ -961,8 +961,8 @@ extern ctl_handler sysctl_ms_jiffies;
/*
* Register a set of sysctl names by calling register_sysctl_table
* with an initialised array of ctl_table's. An entry with zero
- * ctl_name terminates the table. table->de will be set up by the
- * registration and need not be initialised in advance.
+ * ctl_name and NULL procname terminates the table. table->de will be
+ * set up by the registration and need not be initialised in advance.
*
* sysctl names can be mirrored automatically under /proc/sys. The
* procname supplied controls /proc naming.
@@ -973,7 +973,10 @@ extern ctl_handler sysctl_ms_jiffies;
* Leaf nodes in the sysctl tree will be represented by a single file
* under /proc; non-leaf nodes will be represented by directories. A
* null procname disables /proc mirroring at this node.
- *
+ *
+ * sysctl entries with a zero ctl_name will not be available through
+ * the binary sysctl interface.
+ *
* sysctl(2) can automatically manage read and write requests through
* the sysctl table. The data and maxlen fields of the ctl_table
* struct enable minimal validation of the values being written to be
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 0c8e805bbd6..09e569f4792 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -1315,7 +1315,9 @@ repeat:
return -ENOTDIR;
if (get_user(n, name))
return -EFAULT;
- for ( ; table->ctl_name; table++) {
+ for ( ; table->ctl_name || table->procname; table++) {
+ if (!table->ctl_name)
+ continue;
if (n == table->ctl_name || table->ctl_name == CTL_ANY) {
int error;
if (table->child) {
@@ -1532,7 +1534,7 @@ static void register_proc_table(ctl_table * table, struct proc_dir_entry *root,
int len;
mode_t mode;
- for (; table->ctl_name; table++) {
+ for (; table->ctl_name || table->procname; table++) {
/* Can't do anything without a proc name. */
if (!table->procname)
continue;
@@ -1579,7 +1581,7 @@ static void register_proc_table(ctl_table * table, struct proc_dir_entry *root,
static void unregister_proc_table(ctl_table * table, struct proc_dir_entry *root)
{
struct proc_dir_entry *de;
- for (; table->ctl_name; table++) {
+ for (; table->ctl_name || table->procname; table++) {
if (!(de = table->de))
continue;
if (de->mode & S_IFDIR) {