/proc/swaps: support polling
System management wants to subscribe to changes in swap configuration.
Make /proc/swaps pollable like /proc/mounts.
[akpm@linux-foundation.org: document proc_poll_event]
Signed-off-by: Kay Sievers <kay.sievers@vrfy.org>
Acked-by: Greg KH <greg@kroah.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 9fc7bac..67ddaaf 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -30,6 +30,7 @@
#include <linux/capability.h>
#include <linux/syscalls.h>
#include <linux/memcontrol.h>
+#include <linux/poll.h>
#include <asm/pgtable.h>
#include <asm/tlbflush.h>
@@ -58,6 +59,10 @@
static DEFINE_MUTEX(swapon_mutex);
+static DECLARE_WAIT_QUEUE_HEAD(proc_poll_wait);
+/* Activity counter to indicate that a swapon or swapoff has occurred */
+static atomic_t proc_poll_event = ATOMIC_INIT(0);
+
static inline unsigned char swap_count(unsigned char ent)
{
return ent & ~SWAP_HAS_CACHE; /* may include SWAP_HAS_CONT flag */
@@ -1680,6 +1685,8 @@
}
filp_close(swap_file, NULL);
err = 0;
+ atomic_inc(&proc_poll_event);
+ wake_up_interruptible(&proc_poll_wait);
out_dput:
filp_close(victim, NULL);
@@ -1688,6 +1695,25 @@
}
#ifdef CONFIG_PROC_FS
+struct proc_swaps {
+ struct seq_file seq;
+ int event;
+};
+
+static unsigned swaps_poll(struct file *file, poll_table *wait)
+{
+ struct proc_swaps *s = file->private_data;
+
+ poll_wait(file, &proc_poll_wait, wait);
+
+ if (s->event != atomic_read(&proc_poll_event)) {
+ s->event = atomic_read(&proc_poll_event);
+ return POLLIN | POLLRDNORM | POLLERR | POLLPRI;
+ }
+
+ return POLLIN | POLLRDNORM;
+}
+
/* iterator */
static void *swap_start(struct seq_file *swap, loff_t *pos)
{
@@ -1771,7 +1797,24 @@
static int swaps_open(struct inode *inode, struct file *file)
{
- return seq_open(file, &swaps_op);
+ struct proc_swaps *s;
+ int ret;
+
+ s = kmalloc(sizeof(struct proc_swaps), GFP_KERNEL);
+ if (!s)
+ return -ENOMEM;
+
+ file->private_data = s;
+
+ ret = seq_open(file, &swaps_op);
+ if (ret) {
+ kfree(s);
+ return ret;
+ }
+
+ s->seq.private = s;
+ s->event = atomic_read(&proc_poll_event);
+ return ret;
}
static const struct file_operations proc_swaps_operations = {
@@ -1779,6 +1822,7 @@
.read = seq_read,
.llseek = seq_lseek,
.release = seq_release,
+ .poll = swaps_poll,
};
static int __init procswaps_init(void)
@@ -2084,6 +2128,9 @@
swap_info[prev]->next = type;
spin_unlock(&swap_lock);
mutex_unlock(&swapon_mutex);
+ atomic_inc(&proc_poll_event);
+ wake_up_interruptible(&proc_poll_wait);
+
error = 0;
goto out;
bad_swap: