[PATCH 6/7] pipe: simplify round_pipe_size()

Eric Biggers
2018-01-08T05:40:00Z

From: Eric Biggers <ebiggers@google.com>

round_pipe_size() calculates the number of pages the requested size
corresponds to, then rounds the page count up to the next power of 2.

However, it also rounds everything < PAGE_SIZE up to PAGE_SIZE.
Therefore, there's no need to actually translate the size into a page
count; we just need to round the size up to the next power of 2.

We do need to verify that bit 31 isn't set, since on 32-bit systems
roundup_pow_of_two() would be undefined in that case. But that can just
be combined with the UINT_MAX check which we need anyway now.

Finally, also remove the check for '!nr_pages' in pipe_set_size(), since
round_pipe_size() always returns either 0 or a multiple of PAGE_SIZE.

Signed-off-by: Eric Biggers <ebiggers@google.com>
---
fs/pipe.c | 15 +++------------
1 file changed, 3 insertions(+), 12 deletions(-)

diff --git a/fs/pipe.c b/fs/pipe.c
index f1ee1e599495..774cafd947dc 100644
--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -1022,20 +1022,14 @@ const struct file_operations pipefifo_fops = {
*/
unsigned int round_pipe_size(unsigned long size)
{
- unsigned long nr_pages;
-
- if (size > UINT_MAX)
+ if (size > (1U << 31))
return 0;

/* Minimum pipe size, as required by POSIX */
if (size < PAGE_SIZE)
- size = PAGE_SIZE;
-
- nr_pages = (size + PAGE_SIZE - 1) >> PAGE_SHIFT;
- if (nr_pages == 0)
- return 0;
+ return PAGE_SIZE;

- return roundup_pow_of_two(nr_pages) << PAGE_SHIFT;
+ return roundup_pow_of_two(size);
}

/*
@@ -1054,9 +1048,6 @@ static long pipe_set_size(struct pipe_inode_info *pipe, unsigned long arg)
return -EINVAL;
nr_pages = size >> PAGE_SHIFT;

- if (!nr_pages)
- return -EINVAL;
-
/*
* If trying to increase the pipe capacity, check that an
* unprivileged user is not trying to exceed various limits
--
2.15.1