linux-kernel - Re: [patch] pipe: add support for shrinking and growing pipes

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Date:	Thu, 03 Jun 2010 13:37:26 +0200
From:	Jens Axboe <jaxboe@...ionio.com>
To:	Miklos Szeredi <miklos@...redi.hu>
CC:	"mtk.manpages@...il.com" <mtk.manpages@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [patch] pipe: add support for shrinking and growing pipes

On 2010-06-03 13:32, Miklos Szeredi wrote:
> On Thu, 03 Jun 2010, Jens Axboe wrote:
>> I looked at that when I did the original pipe-max-pages, but it seems
>> we're not consistent in this regard. Anyway, here's what I came up with.
>> Not tested yet, and I hope thunderbird doesn't fsck up the patch.
> 
> Unfortunately it did (line wrap damage).

I suspected it might. This better?

diff --git a/fs/pipe.c b/fs/pipe.c
index f98fae3..f7f62f3 100644
--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -26,9 +26,14 @@

 /*
  * The max size that a non-root user is allowed to grow the pipe. Can
- * be set by root in /proc/sys/fs/pipe-max-pages
+ * be set by root in /proc/sys/fs/pipe_max_size
  */
-unsigned int pipe_max_pages = PIPE_DEF_BUFFERS * 16;
+unsigned int pipe_max_size = 1048576;
+
+/*
+ * Minimum pipe size, as required by POSIX
+ */
+unsigned int pipe_min_size = PAGE_SIZE;

 /*
  * We use a start+len construction, which provides full use of the
@@ -1156,6 +1161,35 @@ static long pipe_set_size(struct pipe_inode_info *pipe, unsigned long nr_pages)
 	return nr_pages * PAGE_SIZE;
 }

+/*
+ * Currently we rely on the pipe array holding a power-of-2 number
+ * of pages.
+ */
+static inline unsigned int round_pipe_size(unsigned int size)
+{
+	unsigned long nr_pages;
+
+	nr_pages = (size + PAGE_SIZE - 1) >> PAGE_SHIFT;
+	return roundup_pow_of_two(nr_pages) << PAGE_SHIFT;
+}
+
+/*
+ * This should work even if CONFIG_PROC_FS isn't set, as proc_dointvec_minmax
+ * will return an error.
+ */
+int pipe_proc_fn(struct ctl_table *table, int write, void __user *buf,
+		 size_t *lenp, loff_t *ppos)
+{
+	int ret;
+
+	ret = proc_dointvec_minmax(table, write, buf, lenp, ppos);
+	if (ret < 0 || !write)
+		return ret;
+
+	pipe_max_size = round_pipe_size(pipe_max_size);
+	return ret;
+}
+
 long pipe_fcntl(struct file *file, unsigned int cmd, unsigned long arg)
 {
 	struct pipe_inode_info *pipe;
@@ -1169,23 +1203,19 @@ long pipe_fcntl(struct file *file, unsigned int cmd, unsigned long arg)

 	switch (cmd) {
 	case F_SETPIPE_SZ: {
-		unsigned long nr_pages;
+		unsigned int size, nr_pages;

-		/*
-		 * Currently the array must be a power-of-2 size, so adjust
-		 * upwards if needed.
-		 */
-		nr_pages = (arg + PAGE_SIZE - 1) >> PAGE_SHIFT;
-		nr_pages = roundup_pow_of_two(nr_pages);
+		size = round_pipe_size(arg);
+		nr_pages = size >> PAGE_SHIFT;

-		if (!capable(CAP_SYS_RESOURCE) && nr_pages > pipe_max_pages) {
+		if (!capable(CAP_SYS_RESOURCE) && size > pipe_max_size) {
 			ret = -EPERM;
 			goto out;
-		} else if (nr_pages < 1) {
+		} else if (nr_pages < PAGE_SIZE) {
 			ret = -EINVAL;
 			goto out;
 		}
-		ret = pipe_set_size(pipe, arg);
+		ret = pipe_set_size(pipe, nr_pages);
 		break;
 		}
 	case F_GETPIPE_SZ:
diff --git a/include/linux/pipe_fs_i.h b/include/linux/pipe_fs_i.h
index 16de393..4457969 100644
--- a/include/linux/pipe_fs_i.h
+++ b/include/linux/pipe_fs_i.h
@@ -139,7 +139,9 @@ void pipe_lock(struct pipe_inode_info *);
 void pipe_unlock(struct pipe_inode_info *);
 void pipe_double_lock(struct pipe_inode_info *, struct pipe_inode_info *);

-extern unsigned int pipe_max_pages;
+extern unsigned int pipe_max_size, pipe_min_size;
+int pipe_proc_fn(struct ctl_table *, int, void __user *, size_t *, loff_t *);
+

 /* Drop the inode semaphore and wait for a pipe event, atomically */
 void pipe_wait(struct pipe_inode_info *pipe);
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 997080f..2f9b3a6 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -1471,12 +1471,12 @@ static struct ctl_table fs_table[] = {
 	},
 #endif
 	{
-		.procname	= "pipe-max-pages",
-		.data		= &pipe_max_pages,
+		.procname	= "pipe_max_size",
+		.data		= &pipe_max_size,
 		.maxlen		= sizeof(int),
 		.mode		= 0644,
-		.proc_handler	= &proc_dointvec_minmax,
-		.extra1		= &two,
+		.proc_handler	= &pipe_proc_fn,
+		.extra1		= &pipe_min_size,
 	},
 /*
  * NOTE: do not add new entries to this table unless you have read

-- 
Jens Axboe

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