Messages in this thread Patch in this message | | | Subject | Re: [PATCH] support polling of /proc/swaps | From | Kay Sievers <> | Date | Wed, 20 Oct 2010 01:25:47 +0200 |
| |
On Tue, 2010-10-19 at 15:31 -0700, Andrew Morton wrote: > On Tue, 19 Oct 2010 11:19:16 +0200 > Kay Sievers <kay.sievers@vrfy.org> wrote:
> It's a bit sad that we have to add quite a pile of infrastructure to > make a procfs file pollable. I wonder if it's possible to provide some > core support for this, and reduce the amount of code at each particular > handler site.
You mean something like adding the event counter to the seq_file? There is /proc/self/mounts,mountinfo and /proc/swaps so far, I think.
> Also, I wonder how we are to communicate the existence of this feature > to our users. Nobody will look in Documentation/filesystems/. Is > there a manpage? Seems not...
Hmm, 'man 5 proc'?
> > +static DECLARE_WAIT_QUEUE_HEAD(proc_poll_wait); > > +static int proc_poll_event; > > Please pick a lock to protect proc_poll_event.
An atomic_t should do it too, right?
> Then document that > locking here, when you also document proc_poll_event ;)
The actual value has no meaning at all, it just tells that something happened if it has changed.
From: Kay Sievers <kay.sievers@vrfy.org> Subject: support polling of /proc/swaps
System management wants to subscribe to changes in swap configuration. Make /proc/swaps pollable like /proc/mounts.
Signed-Off-By: Kay Sievers <kay.sievers@vrfy.org> --- mm/swapfile.c | 48 +++++++++++++++++++++++++++++++++++++++++++++++- 1 file changed, 47 insertions(+), 1 deletion(-)
--- 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 +59,9 @@ static struct swap_info_struct *swap_inf static DEFINE_MUTEX(swapon_mutex); +static DECLARE_WAIT_QUEUE_HEAD(proc_poll_wait); +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 +1684,8 @@ SYSCALL_DEFINE1(swapoff, const char __us } 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 +1694,25 @@ out: } #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 +1796,24 @@ static const struct seq_operations swaps 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 +1821,7 @@ static const struct file_operations proc .read = seq_read, .llseek = seq_lseek, .release = seq_release, + .poll = swaps_poll, }; static int __init procswaps_init(void) @@ -2084,6 +2127,9 @@ SYSCALL_DEFINE2(swapon, const char __use 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:
| |