Re: [PATCH] sysctl: add support for poll()

From: Kay Sievers
Date: Mon Jun 13 2011 - 12:06:02 EST

On Thu, 2011-06-09 at 15:16 +0200, Kay Sievers wrote:
> On Thu, Jun 9, 2011 at 00:17, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> 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

---
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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