[PATCH] make /proc/mounts pollable

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 47 insertions, 15 deletions

diff --git a/fs/proc/base.c b/fs/proc/base.c
index a170450aadb1..634355e16986 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -70,6 +70,7 @@
 #include <linux/seccomp.h>
 #include <linux/cpuset.h>
 #include <linux/audit.h>
+#include <linux/poll.h>
 #include "internal.h"
 
 /*
@@ -660,26 +661,38 @@ static struct file_operations proc_smaps_operations = {
 #endif
 
 extern struct seq_operations mounts_op;
+struct proc_mounts {
+        struct seq_file m;
+        int event;
+};
+
 static int mounts_open(struct inode *inode, struct file *file)
 {
         struct task_struct *task = proc_task(inode);
-        int ret = seq_open(file, &mounts_op);
+        struct namespace *namespace;
+        struct proc_mounts *p;
+        int ret = -EINVAL;
 
-        if (!ret) {
-                struct seq_file *m = file->private_data;
-                struct namespace *namespace;
-                task_lock(task);
-                namespace = task->namespace;
-                if (namespace)
-                        get_namespace(namespace);
-                task_unlock(task);
-
-                if (namespace)
-                        m->private = namespace;
-                else {
-                        seq_release(inode, file);
-                        ret = -EINVAL;
+        task_lock(task);
+        namespace = task->namespace;
+        if (namespace)
+                get_namespace(namespace);
+        task_unlock(task);
+
+        if (namespace) {
+                ret = -ENOMEM;
+                p = kmalloc(sizeof(struct proc_mounts), GFP_KERNEL);
+                if (p) {
+                        file->private_data = &p->m;
+                        ret = seq_open(file, &mounts_op);
+                        if (!ret) {
+                                p->m.private = namespace;
+                                p->event = namespace->event;
+                                return 0;
+                        }
+                        kfree(p);
                 }
+                put_namespace(namespace);
         }
         return ret;
 }
@@ -692,11 +705,30 @@ static int mounts_release(struct inode *inode, struct file *file)
         return seq_release(inode, file);
 }
 
+static unsigned mounts_poll(struct file *file, poll_table *wait)
+{
+        struct proc_mounts *p = file->private_data;
+        struct namespace *ns = p->m.private;
+        unsigned res = 0;
+
+        poll_wait(file, &ns->poll, wait);
+
+        spin_lock(&vfsmount_lock);
+        if (p->event != ns->event) {
+                p->event = ns->event;
+                res = POLLERR;
+        }
+        spin_unlock(&vfsmount_lock);
+
+        return res;
+}
+
 static struct file_operations proc_mounts_operations = {
         .open           = mounts_open,
         .read           = seq_read,
         .llseek         = seq_lseek,
         .release        = mounts_release,
+        .poll           = mounts_poll,
 };
 
 #define PROC_BLOCK_SIZE (3*1024)                /* 4K page size but our output routines use some slack for overruns */