cgroups: support named cgroups hierarchies

To simplify referring to cgroup hierarchies in mount statements, and to
allow disambiguation in the presence of empty hierarchies and
multiply-bindable subsystems this patch adds support for naming a new
cgroup hierarchy via the "name=" mount option

A pre-existing hierarchy may be specified by either name or by subsystems;
a hierarchy's name cannot be changed by a remount operation.

Example usage:

# To create a hierarchy called "foo" containing the "cpu" subsystem
mount -t cgroup -oname=foo,cpu cgroup /mnt/cgroup1

# To mount the "foo" hierarchy on a second location
mount -t cgroup -oname=foo cgroup /mnt/cgroup2

Signed-off-by: Paul Menage <menage@google.com>
Reviewed-by: Li Zefan <lizf@cn.fujitsu.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Dhaval Giani <dhaval@linux.vnet.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 156 insertions, 48 deletions

diff --git a/Documentation/cgroups/cgroups.txt b/Documentation/cgroups/cgroups.txt
index 6eb1a97e88ce..4bccfc19196b 100644
--- a/Documentation/cgroups/cgroups.txt
+++ b/Documentation/cgroups/cgroups.txt
@@ -408,6 +408,26 @@ You can attach the current shell task by echoing 0:
 
 # echo 0 > tasks
 
+2.3 Mounting hierarchies by name
+--------------------------------
+
+Passing the name=<x> option when mounting a cgroups hierarchy
+associates the given name with the hierarchy.  This can be used when
+mounting a pre-existing hierarchy, in order to refer to it by name
+rather than by its set of active subsystems.  Each hierarchy is either
+nameless, or has a unique name.
+
+The name should match [\w.-]+
+
+When passing a name=<x> option for a new hierarchy, you need to
+specify subsystems manually; the legacy behaviour of mounting all
+subsystems when none are explicitly specified is not supported when
+you give a subsystem a name.
+
+The name of the subsystem appears as part of the hierarchy description
+in /proc/mounts and /proc/<pid>/cgroups.
+
+
 3. Kernel API
 =============
 
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index f5281aadbcab..03204044622f 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -23,6 +23,7 @@
  */
 
 #include <linux/cgroup.h>
+#include <linux/ctype.h>
 #include <linux/errno.h>
 #include <linux/fs.h>
 #include <linux/kernel.h>
@@ -60,6 +61,8 @@ static struct cgroup_subsys *subsys[] = {
 #include <linux/cgroup_subsys.h>
 };
 
+#define MAX_CGROUP_ROOT_NAMELEN 64
+
 /*
  * A cgroupfs_root represents the root of a cgroup hierarchy,
  * and may be associated with a superblock to form an active
@@ -94,6 +97,9 @@ struct cgroupfs_root {
 
         /* The path to use for release notifications. */
         char release_agent_path[PATH_MAX];
+
+        /* The name for this hierarchy - may be empty */
+        char name[MAX_CGROUP_ROOT_NAMELEN];
 };
 
 /*
@@ -841,6 +847,8 @@ static int cgroup_show_options(struct seq_file *seq, struct vfsmount *vfs)
                 seq_puts(seq, ",noprefix");
         if (strlen(root->release_agent_path))
                 seq_printf(seq, ",release_agent=%s", root->release_agent_path);
+        if (strlen(root->name))
+                seq_printf(seq, ",name=%s", root->name);
         mutex_unlock(&cgroup_mutex);
         return 0;
 }
@@ -849,6 +857,9 @@ struct cgroup_sb_opts {
         unsigned long subsys_bits;
         unsigned long flags;
         char *release_agent;
+        char *name;
+
+        struct cgroupfs_root *new_root;
 };
 
 /* Convert a hierarchy specifier into a bitmask of subsystems and
@@ -863,9 +874,7 @@ static int parse_cgroupfs_options(char *data,
         mask = ~(1UL << cpuset_subsys_id);
 #endif
 
-        opts->subsys_bits = 0;
-        opts->flags = 0;
-        opts->release_agent = NULL;
+        memset(opts, 0, sizeof(*opts));
 
         while ((token = strsep(&o, ",")) != NULL) {
                 if (!*token)
@@ -885,11 +894,33 @@ static int parse_cgroupfs_options(char *data,
                         /* Specifying two release agents is forbidden */
                         if (opts->release_agent)
                                 return -EINVAL;
-                        opts->release_agent = kzalloc(PATH_MAX, GFP_KERNEL);
+                        opts->release_agent =
+                                kstrndup(token + 14, PATH_MAX, GFP_KERNEL);
                         if (!opts->release_agent)
                                 return -ENOMEM;
-                        strncpy(opts->release_agent, token + 14, PATH_MAX - 1);
-                        opts->release_agent[PATH_MAX - 1] = 0;
+                } else if (!strncmp(token, "name=", 5)) {
+                        int i;
+                        const char *name = token + 5;
+                        /* Can't specify an empty name */
+                        if (!strlen(name))
+                                return -EINVAL;
+                        /* Must match [\w.-]+ */
+                        for (i = 0; i < strlen(name); i++) {
+                                char c = name[i];
+                                if (isalnum(c))
+                                        continue;
+                                if ((c == '.') || (c == '-') || (c == '_'))
+                                        continue;
+                                return -EINVAL;
+                        }
+                        /* Specifying two names is forbidden */
+                        if (opts->name)
+                                return -EINVAL;
+                        opts->name = kstrndup(name,
+                                              MAX_CGROUP_ROOT_NAMELEN,
+                                              GFP_KERNEL);
+                        if (!opts->name)
+                                return -ENOMEM;
                 } else {
                         struct cgroup_subsys *ss;
                         int i;
@@ -916,7 +947,7 @@ static int parse_cgroupfs_options(char *data,
                 return -EINVAL;
 
         /* We can't have an empty hierarchy */
-        if (!opts->subsys_bits)
+        if (!opts->subsys_bits && !opts->name)
                 return -EINVAL;
 
         return 0;
@@ -944,6 +975,12 @@ static int cgroup_remount(struct super_block *sb, int *flags, char *data)
                 goto out_unlock;
         }
 
+        /* Don't allow name to change at remount */
+        if (opts.name && strcmp(opts.name, root->name)) {
+                ret = -EINVAL;
+                goto out_unlock;
+        }
+
         ret = rebind_subsystems(root, opts.subsys_bits);
         if (ret)
                 goto out_unlock;
@@ -955,6 +992,7 @@ static int cgroup_remount(struct super_block *sb, int *flags, char *data)
                 strcpy(root->release_agent_path, opts.release_agent);
  out_unlock:
         kfree(opts.release_agent);
+        kfree(opts.name);
         mutex_unlock(&cgroup_mutex);
         mutex_unlock(&cgrp->dentry->d_inode->i_mutex);
         unlock_kernel();
@@ -977,6 +1015,7 @@ static void init_cgroup_housekeeping(struct cgroup *cgrp)
         INIT_LIST_HEAD(&cgrp->pids_list);
         init_rwsem(&cgrp->pids_mutex);
 }
+
 static void init_cgroup_root(struct cgroupfs_root *root)
 {
         struct cgroup *cgrp = &root->top_cgroup;
@@ -990,31 +1029,59 @@ static void init_cgroup_root(struct cgroupfs_root *root)
 
 static int cgroup_test_super(struct super_block *sb, void *data)
 {
-        struct cgroupfs_root *new = data;
+        struct cgroup_sb_opts *opts = data;
         struct cgroupfs_root *root = sb->s_fs_info;
 
-        /* First check subsystems */
-        if (new->subsys_bits != root->subsys_bits)
-            return 0;
+        /* If we asked for a name then it must match */
+        if (opts->name && strcmp(opts->name, root->name))
+                return 0;
 
-        /* Next check flags */
-        if (new->flags != root->flags)
+        /* If we asked for subsystems then they must match */
+        if (opts->subsys_bits && (opts->subsys_bits != root->subsys_bits))
                 return 0;
 
         return 1;
 }
 
+static struct cgroupfs_root *cgroup_root_from_opts(struct cgroup_sb_opts *opts)
+{
+        struct cgroupfs_root *root;
+
+        /* Empty hierarchies aren't supported */
+        if (!opts->subsys_bits)
+                return NULL;
+
+        root = kzalloc(sizeof(*root), GFP_KERNEL);
+        if (!root)
+                return ERR_PTR(-ENOMEM);
+
+        init_cgroup_root(root);
+        root->subsys_bits = opts->subsys_bits;
+        root->flags = opts->flags;
+        if (opts->release_agent)
+                strcpy(root->release_agent_path, opts->release_agent);
+        if (opts->name)
+                strcpy(root->name, opts->name);
+        return root;
+}
+
 static int cgroup_set_super(struct super_block *sb, void *data)
 {
         int ret;
-        struct cgroupfs_root *root = data;
+        struct cgroup_sb_opts *opts = data;
+
+        /* If we don't have a new root, we can't set up a new sb */
+        if (!opts->new_root)
+                return -EINVAL;
+
+        BUG_ON(!opts->subsys_bits);
 
         ret = set_anon_super(sb, NULL);
         if (ret)
                 return ret;
 
-        sb->s_fs_info = root;
-        root->sb = sb;
+        sb->s_fs_info = opts->new_root;
+        opts->new_root->sb = sb;
 
         sb->s_blocksize = PAGE_CACHE_SIZE;
         sb->s_blocksize_bits = PAGE_CACHE_SHIFT;
@@ -1051,48 +1118,43 @@ static int cgroup_get_sb(struct file_system_type *fs_type,
                          void *data, struct vfsmount *mnt)
 {
         struct cgroup_sb_opts opts;
+        struct cgroupfs_root *root;
         int ret = 0;
         struct super_block *sb;
-        struct cgroupfs_root *root;
-        struct list_head tmp_cg_links;
+        struct cgroupfs_root *new_root;
 
         /* First find the desired set of subsystems */
         ret = parse_cgroupfs_options(data, &opts);
-        if (ret) {
-                kfree(opts.release_agent);
-                return ret;
-        }
-
-        root = kzalloc(sizeof(*root), GFP_KERNEL);
-        if (!root) {
-                kfree(opts.release_agent);
-                return -ENOMEM;
-        }
+        if (ret)
+                goto out_err;
 
-        init_cgroup_root(root);
-        root->subsys_bits = opts.subsys_bits;
-        root->flags = opts.flags;
-        if (opts.release_agent) {
-                strcpy(root->release_agent_path, opts.release_agent);
-                kfree(opts.release_agent);
+        /*
+         * Allocate a new cgroup root. We may not need it if we're
+         * reusing an existing hierarchy.
+         */
+        new_root = cgroup_root_from_opts(&opts);
+        if (IS_ERR(new_root)) {
+                ret = PTR_ERR(new_root);
+                goto out_err;
         }
+        opts.new_root = new_root;
 
-        sb = sget(fs_type, cgroup_test_super, cgroup_set_super, root);
-
+        /* Locate an existing or new sb for this hierarchy */
+        sb = sget(fs_type, cgroup_test_super, cgroup_set_super, &opts);
         if (IS_ERR(sb)) {
-                kfree(root);
-                return PTR_ERR(sb);
+                ret = PTR_ERR(sb);
+                kfree(opts.new_root);
+                goto out_err;
         }
 
-        if (sb->s_fs_info != root) {
-                /* Reusing an existing superblock */
-                BUG_ON(sb->s_root == NULL);
-                kfree(root);
-                root = NULL;
-        } else {
-                /* New superblock */
+        root = sb->s_fs_info;
+        BUG_ON(!root);
+        if (root == opts.new_root) {
+                /* We used the new root structure, so this is a new hierarchy */
+                struct list_head tmp_cg_links;
                 struct cgroup *root_cgrp = &root->top_cgroup;
                 struct inode *inode;
+                struct cgroupfs_root *existing_root;
                 int i;
 
                 BUG_ON(sb->s_root != NULL);
@@ -1105,6 +1167,18 @@ static int cgroup_get_sb(struct file_system_type *fs_type,
                 mutex_lock(&inode->i_mutex);
                 mutex_lock(&cgroup_mutex);
 
+                if (strlen(root->name)) {
+                        /* Check for name clashes with existing mounts */
+                        for_each_active_root(existing_root) {
+                                if (!strcmp(existing_root->name, root->name)) {
+                                        ret = -EBUSY;
+                                        mutex_unlock(&cgroup_mutex);
+                                        mutex_unlock(&inode->i_mutex);
+                                        goto drop_new_super;
+                                }
+                        }
+                }
+
                 /*
                  * We're accessing css_set_count without locking
                  * css_set_lock here, but that's OK - it can only be
@@ -1123,7 +1197,8 @@ static int cgroup_get_sb(struct file_system_type *fs_type,
                 if (ret == -EBUSY) {
                         mutex_unlock(&cgroup_mutex);
                         mutex_unlock(&inode->i_mutex);
-                        goto free_cg_links;
+                        free_cg_links(&tmp_cg_links);
+                        goto drop_new_super;
                 }
 
                 /* EBUSY should be the only error here */
@@ -1157,15 +1232,25 @@ static int cgroup_get_sb(struct file_system_type *fs_type,
                 cgroup_populate_dir(root_cgrp);
                 mutex_unlock(&cgroup_mutex);
                 mutex_unlock(&inode->i_mutex);
+        } else {
+                /*
+                 * We re-used an existing hierarchy - the new root (if
+                 * any) is not needed
+                 */
+                kfree(opts.new_root);
         }
 
         simple_set_mnt(mnt, sb);
+        kfree(opts.release_agent);
+        kfree(opts.name);
         return 0;
 
- free_cg_links:
-        free_cg_links(&tmp_cg_links);
  drop_new_super:
         deactivate_locked_super(sb);
+ out_err:
+        kfree(opts.release_agent);
+        kfree(opts.name);
+
         return ret;
 }
 
@@ -2992,6 +3077,9 @@ static int proc_cgroup_show(struct seq_file *m, void *v)
                 seq_printf(m, "%lu:", root->subsys_bits);
                 for_each_subsys(root, ss)
                         seq_printf(m, "%s%s", count++ ? "," : "", ss->name);
+                if (strlen(root->name))
+                        seq_printf(m, "%sname=%s", count ? "," : "",
+                                   root->name);
                 seq_putc(m, ':');
                 get_first_subsys(&root->top_cgroup, NULL, &subsys_id);
                 cgrp = task_cgroup(tsk, subsys_id);