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Date: Tue, 14 Jun 2011 14:17:35 +1000
From: NeilBrown <neilb@...e.de>
To: Kay Sievers <kay.sievers@...y.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
"Eric W. Biederman" <ebiederm@...ssion.com>,
Lucas De Marchi <lucas.demarchi@...fusion.mobi>,
Alan Cox <alan@...rguk.ukuu.org.uk>,
linux-kernel@...r.kernel.org, Nick Piggin <npiggin@...nel.dk>,
Al Viro <viro@...iv.linux.org.uk>,
Christoph Hellwig <hch@....de>,
Stephen Rothwell <sfr@...b.auug.org.au>,
David Howells <dhowells@...hat.com>,
"Serge E. Hallyn" <serge.hallyn@...onical.com>,
Daniel Lezcano <daniel.lezcano@...e.fr>,
Jiri Slaby <jslaby@...e.cz>,
Greg Kroah-Hartman <gregkh@...e.de>,
James Morris <jmorris@...ei.org>
Subject: Re: [PATCH] sysctl: add support for poll()
On Mon, 13 Jun 2011 18:05:51 +0200 Kay Sievers <kay.sievers@...y.org> wrote:
> On Thu, 2011-06-09 at 15:16 +0200, Kay Sievers wrote:
> > On Thu, Jun 9, 2011 at 00:17, Andrew Morton <akpm@...ux-foundation.org> wrote:
>
> > > We already have several pollable procfs files, such as
> > > fs/proc/base.c:mounts_poll() and I think drivers/md has one. I do
> > > think that any work in this area should end up with those custom
> > > make-procfs-pollable hacks being identified and removed.
> >
> > For these files we can probably move the event counter into the
> > seq_file structure, and get rid of the dance to kmalloc it and assign
> > it to seq_file->private. That might simplify the logic a bit.
> >
> > [Adding Neil, to get his opinion of moving 'event' so seq_file and get
> > rid of the malloc dance]
>
> I guess, we could do something like this, which looks quite a bit
> simpler by moving the poll event counter into the dynamically allocated
> seq_file structure itself, instead of having private structures
> allocated on top to just carry the counter (patch is just
> compile-tested).
>
> Thanks,
> Kay
Acked-by: NeilBrown <neilb@...e.de>
Looks like a nice improvement - thanks.
It is a pity that files don't all respond the same way to select/poll though.
Some set POLLIN|POLLRDNORM always, some set it only when there is a new event.
I have found that the former is safer. There are some frameworks that always
use select/poll before reading, and get confused when they cannot read from
some /proc file.
And uniformity is good anyway.
NeilBrown
>
> ---
> drivers/md/md.c | 26 ++++++++------------------
> fs/namespace.c | 4 ++--
> fs/proc/base.c | 2 +-
> include/linux/mnt_namespace.h | 1 -
> include/linux/seq_file.h | 1 +
> mm/swapfile.c | 29 ++++++++---------------------
> 6 files changed, 20 insertions(+), 43 deletions(-)
>
> diff --git a/drivers/md/md.c b/drivers/md/md.c
> index aa640a8..b073d36 100644
> --- a/drivers/md/md.c
> +++ b/drivers/md/md.c
> @@ -6377,16 +6377,11 @@ static void md_seq_stop(struct seq_file *seq, void *v)
> mddev_put(mddev);
> }
>
> -struct mdstat_info {
> - int event;
> -};
> -
> static int md_seq_show(struct seq_file *seq, void *v)
> {
> mddev_t *mddev = v;
> sector_t sectors;
> mdk_rdev_t *rdev;
> - struct mdstat_info *mi = seq->private;
> struct bitmap *bitmap;
>
> if (v == (void*)1) {
> @@ -6398,7 +6393,7 @@ static int md_seq_show(struct seq_file *seq, void *v)
>
> spin_unlock(&pers_lock);
> seq_printf(seq, "\n");
> - mi->event = atomic_read(&md_event_count);
> + seq->poll_event = atomic_read(&md_event_count);
> return 0;
> }
> if (v == (void*)2) {
> @@ -6510,26 +6505,21 @@ static const struct seq_operations md_seq_ops = {
>
> static int md_seq_open(struct inode *inode, struct file *file)
> {
> + struct seq_file *seq;
> int error;
> - struct mdstat_info *mi = kmalloc(sizeof(*mi), GFP_KERNEL);
> - if (mi == NULL)
> - return -ENOMEM;
>
> error = seq_open(file, &md_seq_ops);
> if (error)
> - kfree(mi);
> - else {
> - struct seq_file *p = file->private_data;
> - p->private = mi;
> - mi->event = atomic_read(&md_event_count);
> - }
> + return error;
> +
> + seq = file->private_data;
> + seq->poll_event = atomic_read(&md_event_count);
> return error;
> }
>
> static unsigned int mdstat_poll(struct file *filp, poll_table *wait)
> {
> - struct seq_file *m = filp->private_data;
> - struct mdstat_info *mi = m->private;
> + struct seq_file *seq = filp->private_data;
> int mask;
>
> poll_wait(filp, &md_event_waiters, wait);
> @@ -6537,7 +6527,7 @@ static unsigned int mdstat_poll(struct file *filp, poll_table *wait)
> /* always allow read */
> mask = POLLIN | POLLRDNORM;
>
> - if (mi->event != atomic_read(&md_event_count))
> + if (seq->poll_event != atomic_read(&md_event_count))
> mask |= POLLERR | POLLPRI;
> return mask;
> }
> diff --git a/fs/namespace.c b/fs/namespace.c
> index fe59bd1..cda50fe 100644
> --- a/fs/namespace.c
> +++ b/fs/namespace.c
> @@ -934,8 +934,8 @@ int mnt_had_events(struct proc_mounts *p)
> int res = 0;
>
> br_read_lock(vfsmount_lock);
> - if (p->event != ns->event) {
> - p->event = ns->event;
> + if (p->m.poll_event != ns->event) {
> + p->m.poll_event = ns->event;
> res = 1;
> }
> br_read_unlock(vfsmount_lock);
> diff --git a/fs/proc/base.c b/fs/proc/base.c
> index 14def99..16d33a3 100644
> --- a/fs/proc/base.c
> +++ b/fs/proc/base.c
> @@ -673,7 +673,7 @@ static int mounts_open_common(struct inode *inode, struct file *file,
> p->m.private = p;
> p->ns = ns;
> p->root = root;
> - p->event = ns->event;
> + p->m.poll_event = ns->event;
>
> return 0;
>
> diff --git a/include/linux/mnt_namespace.h b/include/linux/mnt_namespace.h
> index 0b89efc..2930485 100644
> --- a/include/linux/mnt_namespace.h
> +++ b/include/linux/mnt_namespace.h
> @@ -18,7 +18,6 @@ struct proc_mounts {
> struct seq_file m; /* must be the first element */
> struct mnt_namespace *ns;
> struct path root;
> - int event;
> };
>
> struct fs_struct;
> diff --git a/include/linux/seq_file.h b/include/linux/seq_file.h
> index 03c0232..be720cd 100644
> --- a/include/linux/seq_file.h
> +++ b/include/linux/seq_file.h
> @@ -23,6 +23,7 @@ struct seq_file {
> u64 version;
> struct mutex lock;
> const struct seq_operations *op;
> + int poll_event;
> void *private;
> };
>
> diff --git a/mm/swapfile.c b/mm/swapfile.c
> index d537d29..5161d7d 100644
> --- a/mm/swapfile.c
> +++ b/mm/swapfile.c
> @@ -1681,19 +1681,14 @@ 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;
> + struct seq_file *seq = 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);
> + if (seq->poll_event != atomic_read(&proc_poll_event)) {
> + seq->poll_event = atomic_read(&proc_poll_event);
> return POLLIN | POLLRDNORM | POLLERR | POLLPRI;
> }
>
> @@ -1783,24 +1778,16 @@ static const struct seq_operations swaps_op = {
>
> static int swaps_open(struct inode *inode, struct file *file)
> {
> - struct proc_swaps *s;
> + struct seq_file *seq;
> 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);
> + if (ret)
> return ret;
> - }
>
> - s->seq.private = s;
> - s->event = atomic_read(&proc_poll_event);
> - return ret;
> + seq = file->private_data;
> + seq->poll_event = atomic_read(&proc_poll_event);
> + return 0;
> }
>
> static const struct file_operations proc_swaps_operations = {
>
>
--
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