3 files changed, 152 insertions, 3 deletions

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 4fe74d156416..0e9a9aa9df64 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -67,6 +67,7 @@
 #include <linux/mount.h>
 #include <linux/security.h>
 #include <linux/ptrace.h>
+#include <linux/cgroup.h>
 #include <linux/cpuset.h>
 #include <linux/audit.h>
 #include <linux/poll.h>
@@ -2133,6 +2134,9 @@ static const struct pid_entry tgid_base_stuff[] = {
 #ifdef CONFIG_CPUSETS
         REG("cpuset",     S_IRUGO, cpuset),
 #endif
+#ifdef CONFIG_CGROUPS
+        REG("cgroup",  S_IRUGO, cgroup),
+#endif
         INF("oom_score",  S_IRUGO, oom_score),
         REG("oom_adj",    S_IRUGO|S_IWUSR, oom_adjust),
 #ifdef CONFIG_AUDITSYSCALL
@@ -2419,6 +2423,9 @@ static const struct pid_entry tid_base_stuff[] = {
 #ifdef CONFIG_CPUSETS
         REG("cpuset",    S_IRUGO, cpuset),
 #endif
+#ifdef CONFIG_CGROUPS
+        REG("cgroup",  S_IRUGO, cgroup),
+#endif
         INF("oom_score", S_IRUGO, oom_score),
         REG("oom_adj",   S_IRUGO|S_IWUSR, oom_adjust),
 #ifdef CONFIG_AUDITSYSCALL
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index b21cf093ac62..a9553568118f 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -29,6 +29,8 @@ extern void cgroup_fork(struct task_struct *p);
 extern void cgroup_fork_callbacks(struct task_struct *p);
 extern void cgroup_exit(struct task_struct *p, int run_callbacks);
 
+extern struct file_operations proc_cgroup_operations;
+
 /* Per-subsystem/per-cgroup state maintained by the system. */
 struct cgroup_subsys_state {
         /* The cgroup that this subsystem is attached to. Useful
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index cc68fe68a60e..db245f19eb8a 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -33,6 +33,7 @@
 #include <linux/mutex.h>
 #include <linux/mount.h>
 #include <linux/pagemap.h>
+#include <linux/proc_fs.h>
 #include <linux/rcupdate.h>
 #include <linux/sched.h>
 #include <linux/seq_file.h>
@@ -247,13 +248,15 @@ static int cgroup_mkdir(struct inode *dir, struct dentry *dentry, int mode);
 static int cgroup_rmdir(struct inode *unused_dir, struct dentry *dentry);
 static int cgroup_populate_dir(struct cgroup *cont);
 static struct inode_operations cgroup_dir_inode_operations;
+static struct file_operations proc_cgroupstats_operations;
+
+static struct backing_dev_info cgroup_backing_dev_info = {
+        .capabilities   = BDI_CAP_NO_ACCT_DIRTY | BDI_CAP_NO_WRITEBACK,
+};
 
 static struct inode *cgroup_new_inode(mode_t mode, struct super_block *sb)
 {
         struct inode *inode = new_inode(sb);
-        static struct backing_dev_info cgroup_backing_dev_info = {
-                .capabilities   = BDI_CAP_NO_ACCT_DIRTY | BDI_CAP_NO_WRITEBACK,
-        };
 
         if (inode) {
                 inode->i_mode = mode;
@@ -1600,6 +1603,11 @@ int __init cgroup_init(void)
 {
         int err;
         int i;
+        struct proc_dir_entry *entry;
+
+        err = bdi_init(&cgroup_backing_dev_info);
+        if (err)
+                return err;
 
         for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
                 struct cgroup_subsys *ss = subsys[i];
@@ -1611,10 +1619,142 @@ int __init cgroup_init(void)
         if (err < 0)
                 goto out;
 
+        entry = create_proc_entry("cgroups", 0, NULL);
+        if (entry)
+                entry->proc_fops = &proc_cgroupstats_operations;
+
 out:
+        if (err)
+                bdi_destroy(&cgroup_backing_dev_info);
+
         return err;
 }
 
+/*
+ * proc_cgroup_show()
+ *  - Print task's cgroup paths into seq_file, one line for each hierarchy
+ *  - Used for /proc/<pid>/cgroup.
+ *  - No need to task_lock(tsk) on this tsk->cgroup reference, as it
+ *    doesn't really matter if tsk->cgroup changes after we read it,
+ *    and we take cgroup_mutex, keeping attach_task() from changing it
+ *    anyway.  No need to check that tsk->cgroup != NULL, thanks to
+ *    the_top_cgroup_hack in cgroup_exit(), which sets an exiting tasks
+ *    cgroup to top_cgroup.
+ */
+
+/* TODO: Use a proper seq_file iterator */
+static int proc_cgroup_show(struct seq_file *m, void *v)
+{
+        struct pid *pid;
+        struct task_struct *tsk;
+        char *buf;
+        int retval;
+        struct cgroupfs_root *root;
+
+        retval = -ENOMEM;
+        buf = kmalloc(PAGE_SIZE, GFP_KERNEL);
+        if (!buf)
+                goto out;
+
+        retval = -ESRCH;
+        pid = m->private;
+        tsk = get_pid_task(pid, PIDTYPE_PID);
+        if (!tsk)
+                goto out_free;
+
+        retval = 0;
+
+        mutex_lock(&cgroup_mutex);
+
+        for_each_root(root) {
+                struct cgroup_subsys *ss;
+                struct cgroup *cont;
+                int subsys_id;
+                int count = 0;
+
+                /* Skip this hierarchy if it has no active subsystems */
+                if (!root->actual_subsys_bits)
+                        continue;
+                for_each_subsys(root, ss)
+                        seq_printf(m, "%s%s", count++ ? "," : "", ss->name);
+                seq_putc(m, ':');
+                get_first_subsys(&root->top_cgroup, NULL, &subsys_id);
+                cont = task_cgroup(tsk, subsys_id);
+                retval = cgroup_path(cont, buf, PAGE_SIZE);
+                if (retval < 0)
+                        goto out_unlock;
+                seq_puts(m, buf);
+                seq_putc(m, '\n');
+        }
+
+out_unlock:
+        mutex_unlock(&cgroup_mutex);
+        put_task_struct(tsk);
+out_free:
+        kfree(buf);
+out:
+        return retval;
+}
+
+static int cgroup_open(struct inode *inode, struct file *file)
+{
+        struct pid *pid = PROC_I(inode)->pid;
+        return single_open(file, proc_cgroup_show, pid);
+}
+
+struct file_operations proc_cgroup_operations = {
+        .open           = cgroup_open,
+        .read           = seq_read,
+        .llseek         = seq_lseek,
+        .release        = single_release,
+};
+
+/* Display information about each subsystem and each hierarchy */
+static int proc_cgroupstats_show(struct seq_file *m, void *v)
+{
+        int i;
+        struct cgroupfs_root *root;
+
+        mutex_lock(&cgroup_mutex);
+        seq_puts(m, "Hierarchies:\n");
+        for_each_root(root) {
+                struct cgroup_subsys *ss;
+                int first = 1;
+                seq_printf(m, "%p: bits=%lx cgroups=%d (", root,
+                           root->subsys_bits, root->number_of_cgroups);
+                for_each_subsys(root, ss) {
+                        seq_printf(m, "%s%s", first ? "" : ", ", ss->name);
+                        first = false;
+                }
+                seq_putc(m, ')');
+                if (root->sb) {
+                        seq_printf(m, " s_active=%d",
+                                   atomic_read(&root->sb->s_active));
+                }
+                seq_putc(m, '\n');
+        }
+        seq_puts(m, "Subsystems:\n");
+        for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
+                struct cgroup_subsys *ss = subsys[i];
+                seq_printf(m, "%d: name=%s hierarchy=%p\n",
+                           i, ss->name, ss->root);
+        }
+        mutex_unlock(&cgroup_mutex);
+        return 0;
+}
+
+static int cgroupstats_open(struct inode *inode, struct file *file)
+{
+        return single_open(file, proc_cgroupstats_show, 0);
+}
+
+static struct file_operations proc_cgroupstats_operations = {
+        .open = cgroupstats_open,
+        .read = seq_read,
+        .llseek = seq_lseek,
+        .release = single_release,
+};
+
 /**
  * cgroup_fork - attach newly forked task to its parents cgroup.
  * @tsk: pointer to task_struct of forking parent process.