Messages in this thread | | | Date | Tue, 19 Oct 2010 15:31:36 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH] support polling of /proc/swaps |
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On Tue, 19 Oct 2010 11:19:16 +0200 Kay Sievers <kay.sievers@vrfy.org> wrote:
> 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. >
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.
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...
> --- > 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 int proc_poll_event;
Please pick a lock to protect proc_poll_event. Then document that locking here, when you also document proc_poll_event ;)
> 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; > + proc_poll_event++;
Then fix this race.
> + wake_up_interruptible(&proc_poll_wait); > > out_dput: > filp_close(victim, NULL);
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