diff mbox

[24/29] sysctl: Replace root_list with links between sysctl_table_sets.

Message ID 1327639925-12920-24-git-send-email-ebiederm@xmission.com
State Not Applicable, archived
Delegated to: David Miller
Headers show

Commit Message

Eric W. Biederman Jan. 27, 2012, 4:52 a.m. UTC 
Piecing together directories by looking first in one directory
tree, than in another directory tree and finally in a third
directory tree makes it hard to verify that some directory
entries are not multiply defined and makes it hard to create
efficient implementations the sysctl filesystem.

Replace the sysctl wide list of roots with autogenerated
links from the core sysctl directory tree to the other
sysctl directory trees.

This simplifies sysctl directory reading and lookups as now
only entries in a single sysctl directory tree need to be
considered.

Benchmark before:
    make-dummies 0 999 -> 0.44s
    rmmod dummy        -> 0.065s
    make-dummies 0 9999 -> 1m36s
    rmmod dummy         -> 0.4s

Benchmark after:
    make-dummies 0 999 -> 0.63s
    rmmod dummy        -> 0.12s
    make-dummies 0 9999 -> 2m35s
    rmmod dummy         -> 18s

The slowdown is caused by the lookups used in insert_headers
and put_links to see if we need to add links or remove links.

Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
---
 fs/proc/proc_sysctl.c  |  397 +++++++++++++++++++++++++++++++++++------------
 include/linux/sysctl.h |    3 +-
 2 files changed, 296 insertions(+), 104 deletions(-)

Comments

Lucian Adrian Grijincu Jan. 30, 2012, 12:01 a.m. UTC | #1 
Very nice way to handle netns specific files with links between sets!

You did a much better job than I did at dealing with them.

It took me a while to understand how the code works. I'll try to write
something for Documentation/ because the inner workings are a bit
intertwined.

A few comments bellow.

On Fri, Jan 27, 2012 at 6:52 AM, Eric W. Biederman
<ebiederm@xmission.com> wrote:
> Piecing together directories by looking first in one directory
> tree, than in another directory tree and finally in a third

than -> then

> directory tree makes it hard to verify that some directory
> entries are not multiply defined and makes it hard to create
> efficient implementations the sysctl filesystem.
>
> Replace the sysctl wide list of roots with autogenerated
> links from the core sysctl directory tree to the other
> sysctl directory trees.
>
> This simplifies sysctl directory reading and lookups as now
> only entries in a single sysctl directory tree need to be
> considered.
>
> Benchmark before:
>    make-dummies 0 999 -> 0.44s
>    rmmod dummy        -> 0.065s
>    make-dummies 0 9999 -> 1m36s
>    rmmod dummy         -> 0.4s
>
> Benchmark after:
>    make-dummies 0 999 -> 0.63s
>    rmmod dummy        -> 0.12s
>    make-dummies 0 9999 -> 2m35s
>    rmmod dummy         -> 18s
>
> The slowdown is caused by the lookups used in insert_headers

insert_headers -> insert_header

> and put_links to see if we need to add links or remove links.




>  void register_sysctl_root(struct ctl_table_root *root)
>  {
> -       spin_lock(&sysctl_lock);
> -       list_add_tail(&root->root_list, &sysctl_table_root.root_list);
> -       spin_unlock(&sysctl_lock);
>  }


This function is empty. Can be deleted (there are two callers in
net/sysctl_net.c.


> @@ -400,6 +373,7 @@ static struct dentry *proc_sys_lookup(struct inode *dir, struct dentry *dentry,
>        struct inode *inode;
>        struct dentry *err = ERR_PTR(-ENOENT);
>        struct ctl_dir *ctl_dir;
> +       int ret;
>
>        if (IS_ERR(head))
>                return ERR_CAST(head);
> @@ -410,6 +384,11 @@ static struct dentry *proc_sys_lookup(struct inode *dir, struct dentry *dentry,
>        if (!p)
>                goto out;
>


"sysctl_follow_link" implies that it will follow the link. I would
pull out the check whether the header is a link or not. This wouldn't
save much (a function call), but it would make the code easier to
read:

	/* Get out quickly if not a link */
        if (S_ISLNK(p->mode)) {
		ret = sysctl_follow_link(&h, &p, current->nsproxy);
		err = ERR_PTR(ret);
		if (ret)
		        goto out;
        }



> +       ret = sysctl_follow_link(&h, &p, current->nsproxy);
> +       err = ERR_PTR(ret);
> +       if (ret)
> +               goto out;
> +
>        err = ERR_PTR(-ENOMEM);
>        inode = proc_sys_make_inode(dir->i_sb, h ? h : head, p);
>        if (h)
> @@ -547,6 +526,25 @@ static int proc_sys_fill_cache(struct file *filp, void *dirent,
>        return !!filldir(dirent, qname.name, qname.len, filp->f_pos, ino, type);
>  }
>
> +static int proc_sys_link_fill_cache(struct file *filp, void *dirent,
> +                                   filldir_t filldir,
> +                                   struct ctl_table_header *head,
> +                                   struct ctl_table *table)
> +{
> +       int err, ret = 0;
> +       head = sysctl_head_grab(head);
> +
> +       /* It is not an error if we can not follow the link ignore it */
> +       err = sysctl_follow_link(&head, &table, current->nsproxy);

similar

> +       if (err)
> +               goto out;
> +
> +       ret = proc_sys_fill_cache(filp, dirent, filldir, head, table);
> +out:
> +       sysctl_head_finish(head);
> +       return ret;
> +}
> +




> -static struct ctl_dir *get_subdir(struct ctl_table_set *set,
> -       struct ctl_dir *dir, const char *name, int namelen)
> +static struct ctl_dir *get_subdir(struct ctl_dir *dir,
> +                                 const char *name, int namelen)
>  {
> +       struct ctl_table_set *set = dir->header.set;
>        struct ctl_dir *subdir, *new = NULL;
>
>        spin_lock(&sysctl_lock);
> -       subdir = find_subdir(dir->header.set, dir, name, namelen);
> -       if (!IS_ERR(subdir))
> -               goto found;
> -       if ((PTR_ERR(subdir) == -ENOENT) && set != dir->header.set)
> -               subdir = find_subdir(set, dir, name, namelen);
> +       subdir = find_subdir(dir, name, namelen);
>        if (!IS_ERR(subdir))
>                goto found;
>        if (PTR_ERR(subdir) != -ENOENT)
> @@ -817,13 +815,14 @@ static struct ctl_dir *get_subdir(struct ctl_table_set *set,
>        if (!new)
>                goto failed;
>
> -       subdir = find_subdir(set, dir, name, namelen);
> +       subdir = find_subdir(dir, name, namelen);
>        if (!IS_ERR(subdir))
>                goto found;
>        if (PTR_ERR(subdir) != -ENOENT)
>                goto failed;

I think you're returning the wrong error here. If we got to this point
then subdir == ERR_PTR(-ENOENT).
We want to create a new dir here even if one doesn't exist.
So if we have an error in insert_header() we don't return that error,
but ENOENT.

>
> -       insert_header(dir, &new->header);
> +       if (insert_header(dir, &new->header))
> +               goto failed;
>        subdir = new;

Something like this would fix it:

        if (subdir = insert_header(dir, &new->header))



>  found:
>        subdir->header.nreg++;
> @@ -841,6 +840,57 @@ failed:
>        return subdir;
>  }
>
Dave Jones Jan. 30, 2012, 5:51 p.m. UTC | #2 
On Thu, Jan 26, 2012 at 08:52:00PM -0800, Eric W. Biederman wrote:

 > +	memset(set, sizeof(*set), 0);

checkpatch should warn you about this mistake.

	Dave
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Eric W. Biederman Jan. 31, 2012, 2:11 a.m. UTC | #3 
Dave Jones <davej@redhat.com> writes:

> On Thu, Jan 26, 2012 at 08:52:00PM -0800, Eric W. Biederman wrote:
>
>  > +	memset(set, sizeof(*set), 0);
>
> checkpatch should warn you about this mistake.

Is there a way to tie checkpatch into git.  Perhaps into git commit?

Having something that would catch this before I embarrassed myself
certainly sounds nice.  However my overall impression of checkpatch
is that it catches newbie mistakes so unless it is trivial to run
checkpatch I don't expect I will run it because I don't expect to
tell me anything useful.

Eric
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Joe Perches Jan. 31, 2012, 2:13 a.m. UTC | #4 
On Mon, 2012-01-30 at 18:11 -0800, Eric W. Biederman wrote:
> Is there a way to tie checkpatch into git.  Perhaps into git commit?

$ git log --format=email -p -1 $commit | \
  ./scripts/checkpatch.pl -

or maybe a front-end script prior to git commit

$ git diff --stat -p <paths> | \
  ./scripts.checkpatch.pl -


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Eric W. Biederman Jan. 31, 2012, 3:10 a.m. UTC | #5 
Lucian Adrian Grijincu <lucian.grijincu@gmail.com> writes:

> Very nice way to handle netns specific files with links between sets!
>
> You did a much better job than I did at dealing with them.
>
> It took me a while to understand how the code works. I'll try to write
> something for Documentation/ because the inner workings are a bit
> intertwined.
>
> A few comments bellow.

Thank you for your review.

I'm going to see how many of your comments I can incorporate into the
code.

Since no significant bugs have been seen my plan is to use incremental
patches on top of the existing code, to address the small issues that
have been seen.  That way I don't have to retest yet again.

>>  void register_sysctl_root(struct ctl_table_root *root)
>>  {
>> -       spin_lock(&sysctl_lock);
>> -       list_add_tail(&root->root_list, &sysctl_table_root.root_list);
>> -       spin_unlock(&sysctl_lock);
>>  }
>
>
> This function is empty. Can be deleted (there are two callers in
> net/sysctl_net.c.

Agreed.  There might be something useful by registering roots.  Perhaps
initialize the default set.  So I have kept the function for the short
term.  register_sysctl_root makes sense as an interface.  We just don't
have anything for register_sysctl_root to do right now.

>> @@ -400,6 +373,7 @@ static struct dentry *proc_sys_lookup(struct inode *dir, struct dentry *dentry,
>>        struct inode *inode;
>>        struct dentry *err = ERR_PTR(-ENOENT);
>>        struct ctl_dir *ctl_dir;
>> +       int ret;
>>
>>        if (IS_ERR(head))
>>                return ERR_CAST(head);
>> @@ -410,6 +384,11 @@ static struct dentry *proc_sys_lookup(struct inode *dir, struct dentry *dentry,
>>        if (!p)
>>                goto out;
>>
>
>
> "sysctl_follow_link" implies that it will follow the link. I would
> pull out the check whether the header is a link or not. This wouldn't
> save much (a function call), but it would make the code easier to
> read:
>
> 	/* Get out quickly if not a link */
>         if (S_ISLNK(p->mode)) {
> 		ret = sysctl_follow_link(&h, &p, current->nsproxy);
> 		err = ERR_PTR(ret);
> 		if (ret)
> 		        goto out;
>         }

Good point, and obviousness is part of what I am aiming for.


>>  {
>> +       struct ctl_table_set *set = dir->header.set;
>>        struct ctl_dir *subdir, *new = NULL;
>>
>>        spin_lock(&sysctl_lock);
>> -       subdir = find_subdir(dir->header.set, dir, name, namelen);
>> -       if (!IS_ERR(subdir))
>> -               goto found;
>> -       if ((PTR_ERR(subdir) == -ENOENT) && set != dir->header.set)
>> -               subdir = find_subdir(set, dir, name, namelen);
>> +       subdir = find_subdir(dir, name, namelen);
>>        if (!IS_ERR(subdir))
>>                goto found;
>>        if (PTR_ERR(subdir) != -ENOENT)
>> @@ -817,13 +815,14 @@ static struct ctl_dir *get_subdir(struct ctl_table_set *set,
>>        if (!new)
>>                goto failed;
>>
>> -       subdir = find_subdir(set, dir, name, namelen);
>> +       subdir = find_subdir(dir, name, namelen);
>>        if (!IS_ERR(subdir))
>>                goto found;
>>        if (PTR_ERR(subdir) != -ENOENT)
>>                goto failed;
>
> I think you're returning the wrong error here. If we got to this point
> then subdir == ERR_PTR(-ENOENT).
> We want to create a new dir here even if one doesn't exist.
> So if we have an error in insert_header() we don't return that error,
> but ENOENT.
>
>>
>> -       insert_header(dir, &new->header);
>> +       if (insert_header(dir, &new->header))
>> +               goto failed;
>>        subdir = new;
>
> Something like this would fix it:
>
>         if (subdir = insert_header(dir, &new->header))
>
>
>
>>  found:
>>        subdir->header.nreg++;
>> @@ -841,6 +840,57 @@ failed:
>>        return subdir;
>>  }
>>
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diff mbox

Patch

diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c
index a785565..ec54a57 100644
--- a/fs/proc/proc_sysctl.c
+++ b/fs/proc/proc_sysctl.c
@@ -32,26 +32,26 @@  static struct ctl_table root_table[] = {
 	},
 	{ }
 };
-static struct ctl_table_root sysctl_table_root;
-static struct ctl_dir sysctl_root_dir = {
-	.header = {
+static struct ctl_table_root sysctl_table_root = {
+	.default_set.list = LIST_HEAD_INIT(sysctl_table_root.default_set.dir.header.ctl_entry),
+	.default_set.dir.header = {
 		{{.count = 1,
 		  .nreg = 1,
 		  .ctl_table = root_table,
 		  .ctl_entry = LIST_HEAD_INIT(sysctl_table_root.default_set.list),}},
+		.ctl_table_arg = root_table,
 		.root = &sysctl_table_root,
 		.set = &sysctl_table_root.default_set,
 	},
 };
-static struct ctl_table_root sysctl_table_root = {
-	.root_list = LIST_HEAD_INIT(sysctl_table_root.root_list),
-	.default_set.list = LIST_HEAD_INIT(sysctl_root_dir.header.ctl_entry),
-	.default_set.root = &sysctl_table_root,
-};
 
 static DEFINE_SPINLOCK(sysctl_lock);
 
 static void drop_sysctl_table(struct ctl_table_header *header);
+static int sysctl_follow_link(struct ctl_table_header **phead,
+	struct ctl_table **pentry, struct nsproxy *namespaces);
+static int insert_links(struct ctl_table_header *head);
+static void put_links(struct ctl_table_header *header);
 
 static void sysctl_print_dir(struct ctl_dir *dir)
 {
@@ -76,9 +76,9 @@  static int namecmp(const char *name1, int len1, const char *name2, int len2)
 }
 
 static struct ctl_table *find_entry(struct ctl_table_header **phead,
-	struct ctl_table_set *set, struct ctl_dir *dir,
-	const char *name, int namelen)
+	struct ctl_dir *dir, const char *name, int namelen)
 {
+	struct ctl_table_set *set = dir->header.set;
 	struct ctl_table_header *head;
 	struct ctl_table *entry;
 
@@ -119,11 +119,21 @@  static void erase_header(struct ctl_table_header *head)
 	list_del_init(&head->ctl_entry);
 }
 
-static void insert_header(struct ctl_dir *dir, struct ctl_table_header *header)
+static int insert_header(struct ctl_dir *dir, struct ctl_table_header *header)
 {
+	int err;
+
+	dir->header.nreg++;
 	header->parent = dir;
-	header->parent->header.nreg++;
+	err = insert_links(header);
+	if (err)
+		goto fail_links;
 	list_add_tail(&header->ctl_entry, &header->set->list);
+	return 0;
+fail_links:
+	header->parent = NULL;
+	drop_sysctl_table(&dir->header);
+	return err;
 }
 
 /* called under sysctl_lock */
@@ -212,72 +222,39 @@  lookup_header_set(struct ctl_table_root *root, struct nsproxy *namespaces)
 	return set;
 }
 
-static struct list_head *
-lookup_header_list(struct ctl_table_root *root, struct nsproxy *namespaces)
-{
-	struct ctl_table_set *set = lookup_header_set(root, namespaces);
-	return &set->list;
-}
-
 static struct ctl_table *lookup_entry(struct ctl_table_header **phead,
 				      struct ctl_dir *dir,
 				      const char *name, int namelen)
 {
 	struct ctl_table_header *head;
 	struct ctl_table *entry;
-	struct ctl_table_root *root;
-	struct ctl_table_set *set;
 
 	spin_lock(&sysctl_lock);
-	root = &sysctl_table_root;
-	do {
-		set = lookup_header_set(root, current->nsproxy);
-		entry = find_entry(&head, set, dir, name, namelen);
-		if (entry && use_table(head))
-			*phead = head;
-		else
-			entry = NULL;
-		root = list_entry(root->root_list.next,
-				  struct ctl_table_root, root_list);
-	} while (!entry && root != &sysctl_table_root);
+	entry = find_entry(&head, dir, name, namelen);
+	if (entry && use_table(head))
+		*phead = head;
+	else
+		entry = NULL;
 	spin_unlock(&sysctl_lock);
 	return entry;
 }
 
 static struct ctl_table_header *next_usable_entry(struct ctl_dir *dir,
-	struct ctl_table_root *root, struct list_head *tmp)
+						  struct list_head *tmp)
 {
-	struct nsproxy *namespaces = current->nsproxy;
-	struct list_head *header_list;
+	struct ctl_table_set *set = dir->header.set;
 	struct ctl_table_header *head;
 
-	goto next;
-	for (;;) {
+	for (tmp = tmp->next; tmp != &set->list; tmp = tmp->next) {
 		head = list_entry(tmp, struct ctl_table_header, ctl_entry);
-		root = head->root;
 
 		if (head->parent != dir ||
 		    !head->ctl_table->procname ||
 		    !use_table(head))
-			goto next;
-
-		return head;
-	next:
-		tmp = tmp->next;
-		header_list = lookup_header_list(root, namespaces);
-		if (tmp != header_list)
 			continue;
 
-		do {
-			root = list_entry(root->root_list.next,
-					struct ctl_table_root, root_list);
-			if (root == &sysctl_table_root)
-				goto out;
-			header_list = lookup_header_list(root, namespaces);
-		} while (list_empty(header_list));
-		tmp = header_list->next;
+		return head;
 	}
-out:
 	return NULL;
 }
 
@@ -288,8 +265,7 @@  static void first_entry(struct ctl_dir *dir,
 	struct ctl_table *entry = NULL;
 
 	spin_lock(&sysctl_lock);
-	head = next_usable_entry(dir, &sysctl_table_root,
-				 &sysctl_table_root.default_set.list);
+	head = next_usable_entry(dir, &dir->header.set->list);
 	spin_unlock(&sysctl_lock);
 	if (head)
 		entry = head->ctl_table;
@@ -306,7 +282,7 @@  static void next_entry(struct ctl_table_header **phead, struct ctl_table **pentr
 	if (!entry->procname) {
 		spin_lock(&sysctl_lock);
 		unuse_table(head);
-		head = next_usable_entry(head->parent, head->root, &head->ctl_entry);
+		head = next_usable_entry(head->parent, &head->ctl_entry);
 		spin_unlock(&sysctl_lock);
 		if (head)
 			entry = head->ctl_table;
@@ -317,9 +293,6 @@  static void next_entry(struct ctl_table_header **phead, struct ctl_table **pentr
 
 void register_sysctl_root(struct ctl_table_root *root)
 {
-	spin_lock(&sysctl_lock);
-	list_add_tail(&root->root_list, &sysctl_table_root.root_list);
-	spin_unlock(&sysctl_lock);
 }
 
 /*
@@ -386,7 +359,7 @@  static struct ctl_table_header *grab_header(struct inode *inode)
 {
 	struct ctl_table_header *head = PROC_I(inode)->sysctl;
 	if (!head)
-		head = &sysctl_root_dir.header;
+		head = &sysctl_table_root.default_set.dir.header;
 	return sysctl_head_grab(head);
 }
 
@@ -400,6 +373,7 @@  static struct dentry *proc_sys_lookup(struct inode *dir, struct dentry *dentry,
 	struct inode *inode;
 	struct dentry *err = ERR_PTR(-ENOENT);
 	struct ctl_dir *ctl_dir;
+	int ret;
 
 	if (IS_ERR(head))
 		return ERR_CAST(head);
@@ -410,6 +384,11 @@  static struct dentry *proc_sys_lookup(struct inode *dir, struct dentry *dentry,
 	if (!p)
 		goto out;
 
+	ret = sysctl_follow_link(&h, &p, current->nsproxy);
+	err = ERR_PTR(ret);
+	if (ret)
+		goto out;
+
 	err = ERR_PTR(-ENOMEM);
 	inode = proc_sys_make_inode(dir->i_sb, h ? h : head, p);
 	if (h)
@@ -547,6 +526,25 @@  static int proc_sys_fill_cache(struct file *filp, void *dirent,
 	return !!filldir(dirent, qname.name, qname.len, filp->f_pos, ino, type);
 }
 
+static int proc_sys_link_fill_cache(struct file *filp, void *dirent,
+				    filldir_t filldir,
+				    struct ctl_table_header *head,
+				    struct ctl_table *table)
+{
+	int err, ret = 0;
+	head = sysctl_head_grab(head);
+
+	/* It is not an error if we can not follow the link ignore it */
+	err = sysctl_follow_link(&head, &table, current->nsproxy);
+	if (err)
+		goto out;
+
+	ret = proc_sys_fill_cache(filp, dirent, filldir, head, table);
+out:
+	sysctl_head_finish(head);
+	return ret;
+}
+
 static int scan(struct ctl_table_header *head, ctl_table *table,
 		unsigned long *pos, struct file *file,
 		void *dirent, filldir_t filldir)
@@ -556,7 +554,10 @@  static int scan(struct ctl_table_header *head, ctl_table *table,
 	if ((*pos)++ < file->f_pos)
 		return 0;
 
-	res = proc_sys_fill_cache(file, dirent, filldir, head, table);
+	if (unlikely(S_ISLNK(table->mode)))
+		res = proc_sys_link_fill_cache(file, dirent, filldir, head, table);
+	else
+		res = proc_sys_fill_cache(file, dirent, filldir, head, table);
 
 	if (res == 0)
 		file->f_pos = *pos;
@@ -757,13 +758,13 @@  static const struct dentry_operations proc_sys_dentry_operations = {
 	.d_compare	= proc_sys_compare,
 };
 
-static struct ctl_dir *find_subdir(struct ctl_table_set *set, struct ctl_dir *dir,
-	const char *name, int namelen)
+static struct ctl_dir *find_subdir(struct ctl_dir *dir,
+				   const char *name, int namelen)
 {
 	struct ctl_table_header *head;
 	struct ctl_table *entry;
 
-	entry = find_entry(&head, set, dir, name, namelen);
+	entry = find_entry(&head, dir, name, namelen);
 	if (!entry)
 		return ERR_PTR(-ENOENT);
 	if (S_ISDIR(entry->mode))
@@ -772,7 +773,7 @@  static struct ctl_dir *find_subdir(struct ctl_table_set *set, struct ctl_dir *di
 }
 
 static struct ctl_dir *new_dir(struct ctl_table_set *set,
-	const char *name, int namelen)
+			       const char *name, int namelen)
 {
 	struct ctl_table *table;
 	struct ctl_dir *new;
@@ -789,22 +790,19 @@  static struct ctl_dir *new_dir(struct ctl_table_set *set,
 	new_name[namelen] = '\0';
 	table[0].procname = new_name;
 	table[0].mode = S_IFDIR|S_IRUGO|S_IXUGO;
-	init_header(&new->header, set->root, set, table);
+	init_header(&new->header, set->dir.header.root, set, table);
 
 	return new;
 }
 
-static struct ctl_dir *get_subdir(struct ctl_table_set *set,
-	struct ctl_dir *dir, const char *name, int namelen)
+static struct ctl_dir *get_subdir(struct ctl_dir *dir,
+				  const char *name, int namelen)
 {
+	struct ctl_table_set *set = dir->header.set;
 	struct ctl_dir *subdir, *new = NULL;
 
 	spin_lock(&sysctl_lock);
-	subdir = find_subdir(dir->header.set, dir, name, namelen);
-	if (!IS_ERR(subdir))
-		goto found;
-	if ((PTR_ERR(subdir) == -ENOENT) && set != dir->header.set)
-		subdir = find_subdir(set, dir, name, namelen);
+	subdir = find_subdir(dir, name, namelen);
 	if (!IS_ERR(subdir))
 		goto found;
 	if (PTR_ERR(subdir) != -ENOENT)
@@ -817,13 +815,14 @@  static struct ctl_dir *get_subdir(struct ctl_table_set *set,
 	if (!new)
 		goto failed;
 
-	subdir = find_subdir(set, dir, name, namelen);
+	subdir = find_subdir(dir, name, namelen);
 	if (!IS_ERR(subdir))
 		goto found;
 	if (PTR_ERR(subdir) != -ENOENT)
 		goto failed;
 
-	insert_header(dir, &new->header);
+	if (insert_header(dir, &new->header))
+		goto failed;
 	subdir = new;
 found:
 	subdir->header.nreg++;
@@ -841,6 +840,57 @@  failed:
 	return subdir;
 }
 
+static struct ctl_dir *xlate_dir(struct ctl_table_set *set, struct ctl_dir *dir)
+{
+	struct ctl_dir *parent;
+	const char *procname;
+	if (!dir->header.parent)
+		return &set->dir;
+	parent = xlate_dir(set, dir->header.parent);
+	if (IS_ERR(parent))
+		return parent;
+	procname = dir->header.ctl_table[0].procname;
+	return find_subdir(parent, procname, strlen(procname));
+}
+
+static int sysctl_follow_link(struct ctl_table_header **phead,
+	struct ctl_table **pentry, struct nsproxy *namespaces)
+{
+	struct ctl_table_header *head;
+	struct ctl_table_root *root;
+	struct ctl_table_set *set;
+	struct ctl_table *entry;
+	struct ctl_dir *dir;
+	int ret;
+
+	/* Get out quickly if not a link */
+	if (!S_ISLNK((*pentry)->mode))
+		return 0;
+
+	ret = 0;
+	spin_lock(&sysctl_lock);
+	root = (*pentry)->data;
+	set = lookup_header_set(root, namespaces);
+	dir = xlate_dir(set, (*phead)->parent);
+	if (IS_ERR(dir))
+		ret = PTR_ERR(dir);
+	else {
+		const char *procname = (*pentry)->procname;
+		head = NULL;
+		entry = find_entry(&head, dir, procname, strlen(procname));
+		ret = -ENOENT;
+		if (entry && use_table(head)) {
+			unuse_table(*phead);
+			*phead = head;
+			*pentry = entry;
+			ret = 0;
+		}
+	}
+
+	spin_unlock(&sysctl_lock);
+	return ret;
+}
+
 static int sysctl_check_table_dups(const char *path, struct ctl_table *old,
 	struct ctl_table *table)
 {
@@ -859,30 +909,21 @@  static int sysctl_check_table_dups(const char *path, struct ctl_table *old,
 	return error;
 }
 
-static int sysctl_check_dups(struct nsproxy *namespaces,
-	struct ctl_dir *dir,
+static int sysctl_check_dups(struct ctl_dir *dir,
 	const char *path, struct ctl_table *table)
 {
-	struct ctl_table_root *root;
 	struct ctl_table_set *set;
 	struct ctl_table_header *head;
 	int error = 0;
 
-	root = &sysctl_table_root;
-	do {
-		set = lookup_header_set(root, namespaces);
-
-		list_for_each_entry(head, &set->list, ctl_entry) {
-			if (head->unregistering)
-				continue;
-			if (head->parent != dir)
-				continue;
-			error = sysctl_check_table_dups(path, head->ctl_table,
-							table);
-		}
-		root = list_entry(root->root_list.next,
-				  struct ctl_table_root, root_list);
-	} while (root != &sysctl_table_root);
+	set = dir->header.set;
+	list_for_each_entry(head, &set->list, ctl_entry) {
+		if (head->unregistering)
+			continue;
+		if (head->parent != dir)
+			continue;
+		error = sysctl_check_table_dups(path, head->ctl_table, table);
+	}
 	return error;
 }
 
@@ -932,6 +973,115 @@  static int sysctl_check_table(const char *path, struct ctl_table *table)
 	return err;
 }
 
+static struct ctl_table_header *new_links(struct ctl_dir *dir, struct ctl_table *table,
+	struct ctl_table_root *link_root)
+{
+	struct ctl_table *link_table, *entry, *link;
+	struct ctl_table_header *links;
+	char *link_name;
+	int nr_entries, name_bytes;
+
+	name_bytes = 0;
+	nr_entries = 0;
+	for (entry = table; entry->procname; entry++) {
+		nr_entries++;
+		name_bytes += strlen(entry->procname) + 1;
+	}
+
+	links = kzalloc(sizeof(struct ctl_table_header) +
+			sizeof(struct ctl_table)*(nr_entries + 1) +
+			name_bytes,
+			GFP_KERNEL);
+
+	if (!links)
+		return NULL;
+
+	link_table = (struct ctl_table *)(links + 1);
+	link_name = (char *)&link_table[nr_entries + 1];
+
+	for (link = link_table, entry = table; entry->procname; link++, entry++) {
+		int len = strlen(entry->procname) + 1;
+		memcpy(link_name, entry->procname, len);
+		link->procname = link_name;
+		link->mode = S_IFLNK|S_IRWXUGO;
+		link->data = link_root;
+		link_name += len;
+	}
+	init_header(links, dir->header.root, dir->header.set, link_table);
+	links->nreg = nr_entries;
+
+	return links;
+}
+
+static bool get_links(struct ctl_dir *dir,
+	struct ctl_table *table, struct ctl_table_root *link_root)
+{
+	struct ctl_table_header *head;
+	struct ctl_table *entry, *link;
+
+	/* Are there links available for every entry in table? */
+	for (entry = table; entry->procname; entry++) {
+		const char *procname = entry->procname;
+		link = find_entry(&head, dir, procname, strlen(procname));
+		if (!link)
+			return false;
+		if (S_ISDIR(link->mode) && S_ISDIR(entry->mode))
+			continue;
+		if (S_ISLNK(link->mode) && (link->data == link_root))
+			continue;
+		return false;
+	}
+
+	/* The checks passed.  Increase the registration count on the links */
+	for (entry = table; entry->procname; entry++) {
+		const char *procname = entry->procname;
+		link = find_entry(&head, dir, procname, strlen(procname));
+		head->nreg++;
+	}
+	return true;
+}
+
+static int insert_links(struct ctl_table_header *head)
+{
+	struct ctl_table_set *root_set = &sysctl_table_root.default_set;
+	struct ctl_dir *core_parent = NULL;
+	struct ctl_table_header *links;
+	int err;
+
+	if (head->set == root_set)
+		return 0;
+
+	core_parent = xlate_dir(root_set, head->parent);
+	if (IS_ERR(core_parent))
+		return 0;
+
+	if (get_links(core_parent, head->ctl_table, head->root))
+		return 0;
+
+	core_parent->header.nreg++;
+	spin_unlock(&sysctl_lock);
+
+	links = new_links(core_parent, head->ctl_table, head->root);
+
+	spin_lock(&sysctl_lock);
+	err = -ENOMEM;
+	if (!links)
+		goto out;
+
+	err = 0;
+	if (get_links(core_parent, head->ctl_table, head->root)) {
+		kfree(links);
+		goto out;
+	}
+
+	err = insert_header(core_parent, links);
+	if (err)
+		kfree(links);
+out:
+	drop_sysctl_table(&core_parent->header);
+	return err;
+}
+
 /**
  * __register_sysctl_table - register a leaf sysctl table
  * @root: List of sysctl headers to register on
@@ -980,6 +1130,7 @@  struct ctl_table_header *__register_sysctl_table(
 	struct nsproxy *namespaces,
 	const char *path, struct ctl_table *table)
 {
+	struct ctl_table_header *links = NULL;
 	struct ctl_table_header *header;
 	const char *name, *nextname;
 	struct ctl_table_set *set;
@@ -995,7 +1146,7 @@  struct ctl_table_header *__register_sysctl_table(
 
 	spin_lock(&sysctl_lock);
 	header->set = set = lookup_header_set(root, namespaces);
-	dir = &sysctl_root_dir;
+	dir = &set->dir;
 	dir->header.nreg++;
 	spin_unlock(&sysctl_lock);
 
@@ -1012,22 +1163,28 @@  struct ctl_table_header *__register_sysctl_table(
 		if (namelen == 0)
 			continue;
 
-		dir = get_subdir(set, dir, name, namelen);
+		dir = get_subdir(dir, name, namelen);
 		if (IS_ERR(dir))
 			goto fail;
 	}
+
 	spin_lock(&sysctl_lock);
-	if (sysctl_check_dups(namespaces, dir, path, table))
+	if (sysctl_check_dups(dir, path, table))
+		goto fail_put_dir_locked;
+
+	if (insert_header(dir, header))
 		goto fail_put_dir_locked;
-	insert_header(dir, header);
+
 	drop_sysctl_table(&dir->header);
 	spin_unlock(&sysctl_lock);
 
 	return header;
+
 fail_put_dir_locked:
 	drop_sysctl_table(&dir->header);
 	spin_unlock(&sysctl_lock);
 fail:
+	kfree(links);
 	kfree(header);
 	dump_stack();
 	return NULL;
@@ -1249,6 +1406,40 @@  struct ctl_table_header *register_sysctl_table(struct ctl_table *table)
 }
 EXPORT_SYMBOL(register_sysctl_table);
 
+static void put_links(struct ctl_table_header *header)
+{
+	struct ctl_table_set *root_set = &sysctl_table_root.default_set;
+	struct ctl_table_root *root = header->root;
+	struct ctl_dir *parent = header->parent;
+	struct ctl_dir *core_parent;
+	struct ctl_table *entry;
+
+	if (header->set == root_set)
+		return;
+
+	core_parent = xlate_dir(root_set, parent);
+	if (IS_ERR(core_parent))
+		return;
+
+	for (entry = header->ctl_table; entry->procname; entry++) {
+		struct ctl_table_header *link_head;
+		struct ctl_table *link;
+		const char *name = entry->procname;
+
+		link = find_entry(&link_head, core_parent, name, strlen(name));
+		if (link &&
+		    ((S_ISDIR(link->mode) && S_ISDIR(entry->mode)) ||
+		     (S_ISLNK(link->mode) && (link->data == root)))) {
+			drop_sysctl_table(link_head);
+		}
+		else {
+			printk(KERN_ERR "sysctl link missing during unregister: ");
+			sysctl_print_dir(parent);
+			printk(KERN_CONT "/%s\n", name);
+		}
+	}
+}
+
 static void drop_sysctl_table(struct ctl_table_header *header)
 {
 	struct ctl_dir *parent = header->parent;
@@ -1256,6 +1447,7 @@  static void drop_sysctl_table(struct ctl_table_header *header)
 	if (--header->nreg)
 		return;
 
+	put_links(header);
 	start_unregistering(header);
 	if (!--header->count)
 		kfree_rcu(header, rcu);
@@ -1301,13 +1493,14 @@  void unregister_sysctl_table(struct ctl_table_header * header)
 }
 EXPORT_SYMBOL(unregister_sysctl_table);
 
-void setup_sysctl_set(struct ctl_table_set *p,
+void setup_sysctl_set(struct ctl_table_set *set,
 	struct ctl_table_root *root,
 	int (*is_seen)(struct ctl_table_set *))
 {
-	INIT_LIST_HEAD(&p->list);
-	p->root = root;
-	p->is_seen = is_seen;
+	memset(set, sizeof(*set), 0);
+	INIT_LIST_HEAD(&set->list);
+	set->is_seen = is_seen;
+	init_header(&set->dir.header, root, set, root_table);
 }
 
 void retire_sysctl_set(struct ctl_table_set *set)
diff --git a/include/linux/sysctl.h b/include/linux/sysctl.h
index 3084b62..2a1446a 100644
--- a/include/linux/sysctl.h
+++ b/include/linux/sysctl.h
@@ -1051,12 +1051,11 @@  struct ctl_dir {
 
 struct ctl_table_set {
 	struct list_head list;
-	struct ctl_table_root *root;
 	int (*is_seen)(struct ctl_table_set *);
+	struct ctl_dir dir;
 };
 
 struct ctl_table_root {
-	struct list_head root_list;
 	struct ctl_table_set default_set;
 	struct ctl_table_set *(*lookup)(struct ctl_table_root *root,
 					   struct nsproxy *namespaces);