pipe: make F_{GET,SET}PIPE_SZ deal with byte sizes

Instead of requiring an exact number of pages as the argument and
return value, change the API to deal with number of bytes instead.

This also relaxes the requirement that the passed in size must
result in a power-of-2 page array size. Round up to the nearest
power-of-2 automatically and return the resulting size of the pipe
on success.
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

fs/pipe.c

@@ -1112,26 +1112,20 @@ SYSCALL_DEFINE1(pipe, int __user *, fildes)
  * Allocate a new array of pipe buffers and copy the info over. Returns the
  * pipe size if successful, or return -ERROR on error.
  */
-static long pipe_set_size(struct pipe_inode_info *pipe, unsigned long arg)
+static long pipe_set_size(struct pipe_inode_info *pipe, unsigned long nr_pages)
 {
 	struct pipe_buffer *bufs;
 
-	/*
-	 * Must be a power-of-2 currently
-	 */
-	if (!is_power_of_2(arg))
-		return -EINVAL;
-
 	/*
 	 * We can shrink the pipe, if arg >= pipe->nrbufs. Since we don't
 	 * expect a lot of shrink+grow operations, just free and allocate
 	 * again like we would do for growing. If the pipe currently
 	 * contains more buffers than arg, then return busy.
 	 */
-	if (arg < pipe->nrbufs)
+	if (nr_pages < pipe->nrbufs)
 		return -EBUSY;
 
-	bufs = kcalloc(arg, sizeof(struct pipe_buffer), GFP_KERNEL);
+	bufs = kcalloc(nr_pages, sizeof(struct pipe_buffer), GFP_KERNEL);
 	if (unlikely(!bufs))
 		return -ENOMEM;
 
@@ -1152,8 +1146,8 @@ static long pipe_set_size(struct pipe_inode_info *pipe, unsigned long arg)
 	pipe->curbuf = 0;
 	kfree(pipe->bufs);
 	pipe->bufs = bufs;
-	pipe->buffers = arg;
-	return arg;
+	pipe->buffers = nr_pages;
+	return nr_pages * PAGE_SIZE;
 }
 
 long pipe_fcntl(struct file *file, unsigned int cmd, unsigned long arg)
@@ -1168,19 +1162,30 @@ long pipe_fcntl(struct file *file, unsigned int cmd, unsigned long arg)
 	mutex_lock(&pipe->inode->i_mutex);
 
 	switch (cmd) {
-	case F_SETPIPE_SZ:
-		if (!capable(CAP_SYS_ADMIN) && arg > pipe_max_pages)
+	case F_SETPIPE_SZ: {
+		unsigned long 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);
+
+		if (!capable(CAP_SYS_ADMIN) && nr_pages > pipe_max_pages)
 			return -EPERM;
+
 		/*
 		 * The pipe needs to be at least 2 pages large to
 		 * guarantee POSIX behaviour.
 		 */
-		if (arg < 2)
+		if (nr_pages < 2)
 			return -EINVAL;
-		ret = pipe_set_size(pipe, arg);
+		ret = pipe_set_size(pipe, nr_pages);
 		break;
+		}
 	case F_GETPIPE_SZ:
-		ret = pipe->buffers;
+		ret = pipe->buffers * PAGE_SIZE;
 		break;
 	default:
 		ret = -EINVAL;