[PATCH v4 3/3] fs: pipe2: Support O_SPECIFIC_FD

[Josh Triplett <josh@joshtriplett.org>]

This allows the caller of pipe2 to specify one or both file descriptors
rather than having them automatically use the lowest available file
descriptor. The caller can specify either file descriptor as -1 to
allow that file descriptor to use the lowest available.

Signed-off-by: Josh Triplett <josh@joshtriplett.org>
---
 fs/pipe.c | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/fs/pipe.c b/fs/pipe.c
index 16fb72e9abf7..4681a0d1d587 100644
--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -936,19 +936,19 @@ static int __do_pipe_flags(int *fd, struct file **files, int flags)
 	int error;
 	int fdw, fdr;
 
-	if (flags & ~(O_CLOEXEC | O_NONBLOCK | O_DIRECT))
+	if (flags & ~(O_CLOEXEC | O_NONBLOCK | O_DIRECT | O_SPECIFIC_FD))
 		return -EINVAL;
 
 	error = create_pipe_files(files, flags);
 	if (error)
 		return error;
 
-	error = get_unused_fd_flags(flags);
+	error = get_specific_unused_fd_flags(fd[0], flags);
 	if (error < 0)
 		goto err_read_pipe;
 	fdr = error;
 
-	error = get_unused_fd_flags(flags);
+	error = get_specific_unused_fd_flags(fd[1], flags);
 	if (error < 0)
 		goto err_fdr;
 	fdw = error;
@@ -969,7 +969,11 @@ static int __do_pipe_flags(int *fd, struct file **files, int flags)
 int do_pipe_flags(int *fd, int flags)
 {
 	struct file *files[2];
-	int error = __do_pipe_flags(fd, files, flags);
+	int error;
+
+	if (flags & O_SPECIFIC_FD)
+		return -EINVAL;
+	error = __do_pipe_flags(fd, files, flags);
 	if (!error) {
 		fd_install(fd[0], files[0]);
 		fd_install(fd[1], files[1]);
@@ -987,6 +991,10 @@ static int do_pipe2(int __user *fildes, int flags)
 	int fd[2];
 	int error;
 
+	if (flags & O_SPECIFIC_FD)
+		if (copy_from_user(fd, fildes, sizeof(fd)))
+			return -EFAULT;
+
 	error = __do_pipe_flags(fd, files, flags);
 	if (!error) {
 		if (unlikely(copy_to_user(fildes, fd, sizeof(fd)))) {
-- 
2.26.0