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SubjectRe: [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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