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Subject[PATCH 1/5] sysctl: faster reimplementation of sysctl_check_table
Date
Determining the parent of a node at depth d
- previous implementation: O(d)
- current implementation: O(1)

Printing the path to a node at depth d
- previous implementation: O(d^2)
- current implementation: O(d)

This comes to a cost: we use an array ('parents') holding as many
pointers as there can be sysctl levels (currently CTL_MAXNAME=10).

The 'parents' array of pointers holds the same values as the
ctl_table->parents field because the function that updates ->parents
(sysctl_set_parent) is called with either NULL (for root nodes) or
with sysctl_set_parent(table, table->child).

Signed-off-by: Lucian Adrian Grijincu <lucian.grijincu@gmail.com>
---
kernel/sysctl_check.c | 121 ++++++++++++++++++++++++-------------------------
1 files changed, 60 insertions(+), 61 deletions(-)
diff --git a/kernel/sysctl_check.c b/kernel/sysctl_check.c
index 10b90d8..9b4fecd 100644
--- a/kernel/sysctl_check.c
+++ b/kernel/sysctl_check.c
@@ -6,58 +6,34 @@
#include <net/ip_vs.h>


-static int sysctl_depth(struct ctl_table *table)
-{
- struct ctl_table *tmp;
- int depth;
-
- depth = 0;
- for (tmp = table; tmp->parent; tmp = tmp->parent)
- depth++;
-
- return depth;
-}
-
-static struct ctl_table *sysctl_parent(struct ctl_table *table, int n)
+static void sysctl_print_path(struct ctl_table *table,
+ struct ctl_table **parents, int depth)
{
+ struct ctl_table *p;
int i;
-
- for (i = 0; table && i < n; i++)
- table = table->parent;
-
- return table;
-}
-
-
-static void sysctl_print_path(struct ctl_table *table)
-{
- struct ctl_table *tmp;
- int depth, i;
- depth = sysctl_depth(table);
if (table->procname) {
- for (i = depth; i >= 0; i--) {
- tmp = sysctl_parent(table, i);
- printk("/%s", tmp->procname?tmp->procname:"");
+ for (i = 0; i < depth; i++) {
+ p = parents[i];
+ printk("/%s", p->procname ? p->procname : "");
}
+ printk("/%s", table->procname);
}
printk(" ");
}

static struct ctl_table *sysctl_check_lookup(struct nsproxy *namespaces,
- struct ctl_table *table)
+ struct ctl_table *table, struct ctl_table **parents, int depth)
{
struct ctl_table_header *head;
struct ctl_table *ref, *test;
- int depth, cur_depth;
-
- depth = sysctl_depth(table);
+ int cur_depth;

for (head = __sysctl_head_next(namespaces, NULL); head;
head = __sysctl_head_next(namespaces, head)) {
cur_depth = depth;
ref = head->ctl_table;
repeat:
- test = sysctl_parent(table, cur_depth);
+ test = parents[depth - cur_depth];
for (; ref->procname; ref++) {
int match = 0;
if (cur_depth && !ref->child)
@@ -83,11 +59,12 @@ out:
return ref;
}

-static void set_fail(const char **fail, struct ctl_table *table, const char *str)
+static void set_fail(const char **fail, struct ctl_table *table,
+ const char *str, struct ctl_table **parents, int depth)
{
if (*fail) {
printk(KERN_ERR "sysctl table check failed: ");
- sysctl_print_path(table);
+ sysctl_print_path(table, parents, depth);
printk(" %s\n", *fail);
dump_stack();
}
@@ -95,16 +72,24 @@ static void set_fail(const char **fail, struct ctl_table *table, const char *str
}

static void sysctl_check_leaf(struct nsproxy *namespaces,
- struct ctl_table *table, const char **fail)
+ struct ctl_table *table, const char **fail,
+ struct ctl_table **parents, int depth)
{
struct ctl_table *ref;

- ref = sysctl_check_lookup(namespaces, table);
- if (ref && (ref != table))
- set_fail(fail, table, "Sysctl already exists");
+ ref = sysctl_check_lookup(namespaces, table, parents, depth);
+ if (ref && (ref != table)) {
+ printk(KERN_ALERT "sysctl_check_leaf ref[%s], table[%s]\n", ref->procname, table->procname);
+ set_fail(fail, table, "Sysctl already exists", parents, depth);
+ }
}

-int sysctl_check_table(struct nsproxy *namespaces, struct ctl_table *table)
+
+
+#define SET_FAIL(str) set_fail(&fail, table, str, parents, depth)
+
+static int __sysctl_check_table(struct nsproxy *namespaces,
+ struct ctl_table *table, struct ctl_table **parents, int depth)
{
int error = 0;
for (; table->procname; table++) {
@@ -112,23 +97,23 @@ int sysctl_check_table(struct nsproxy *namespaces, struct ctl_table *table)

if (table->parent) {
if (table->procname && !table->parent->procname)
- set_fail(&fail, table, "Parent without procname");
+ SET_FAIL("Parent without procname");
}
if (!table->procname)
- set_fail(&fail, table, "No procname");
+ SET_FAIL("No procname");
if (table->child) {
if (table->data)
- set_fail(&fail, table, "Directory with data?");
+ SET_FAIL("Directory with data?");
if (table->maxlen)
- set_fail(&fail, table, "Directory with maxlen?");
+ SET_FAIL("Directory with maxlen?");
if ((table->mode & (S_IRUGO|S_IXUGO)) != table->mode)
- set_fail(&fail, table, "Writable sysctl directory");
+ SET_FAIL("Writable sysctl directory");
if (table->proc_handler)
- set_fail(&fail, table, "Directory with proc_handler");
+ SET_FAIL("Directory with proc_handler");
if (table->extra1)
- set_fail(&fail, table, "Directory with extra1");
+ SET_FAIL("Directory with extra1");
if (table->extra2)
- set_fail(&fail, table, "Directory with extra2");
+ SET_FAIL("Directory with extra2");
} else {
if ((table->proc_handler == proc_dostring) ||
(table->proc_handler == proc_dointvec) ||
@@ -139,28 +124,42 @@ int sysctl_check_table(struct nsproxy *namespaces, struct ctl_table *table)
(table->proc_handler == proc_doulongvec_minmax) ||
(table->proc_handler == proc_doulongvec_ms_jiffies_minmax)) {
if (!table->data)
- set_fail(&fail, table, "No data");
+ SET_FAIL("No data");
if (!table->maxlen)
- set_fail(&fail, table, "No maxlen");
+ SET_FAIL("No maxlen");
}
#ifdef CONFIG_PROC_SYSCTL
if (table->procname && !table->proc_handler)
- set_fail(&fail, table, "No proc_handler");
-#endif
-#if 0
- if (!table->procname && table->proc_handler)
- set_fail(&fail, table, "proc_handler without procname");
+ SET_FAIL("No proc_handler");
#endif
- sysctl_check_leaf(namespaces, table, &fail);
+ parents[depth] = table;
+ sysctl_check_leaf(namespaces, table, &fail,
+ parents, depth);
}
if (table->mode > 0777)
- set_fail(&fail, table, "bogus .mode");
+ SET_FAIL("bogus .mode");
if (fail) {
- set_fail(&fail, table, NULL);
+ SET_FAIL(NULL);
error = -EINVAL;
}
- if (table->child)
- error |= sysctl_check_table(namespaces, table->child);
+ if (table->child) {
+ parents[depth] = table;
+ error |= __sysctl_check_table(namespaces, table->child,
+ parents, depth + 1);
+ }
}
return error;
}
+
+
+int sysctl_check_table(struct nsproxy *namespaces, struct ctl_table *table)
+{
+ struct ctl_table *parents[CTL_MAXNAME];
+ /* Keep track of parents as we go down into the tree.
+ *
+ * parents[i-1] will be the parent for parents[i].
+ * The node at depth 'd' will have the parent at parents[d-1].
+ * The root node (depth=0) has no parent in this array.
+ */
+ return __sysctl_check_table(namespaces, table, parents, 0);
+}
--
1.7.4.rc1.7.g2cf08.dirty


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