Re: [PATCH][RFC] open_tree(2) (was Re: [PATCH 30/32] vfs: Allow cloning of a mount tree with open(O_PATH|O_CLONE_MOUNT) [ver #8])

On Mon, Jun 4, 2018 at 7:35 PM, Al Viro [off-list ref] wrote:

On Mon, Jun 04, 2018 at 10:16:30AM -0700, Matthew Wilcox wrote:

quoted

On Sun, Jun 03, 2018 at 01:55:37AM +0100, Al Viro wrote:

quoted

+SYSCALL_DEFINE3(open_tree, int, dfd, const char *, filename, unsigned, flags)
+{
+   struct file *file;
+   struct path path;
+   int lookup_flags = LOOKUP_AUTOMOUNT | LOOKUP_FOLLOW;
+   bool detached = flags & OPEN_TREE_CLONE;
+   int error;
+   int fd;
+
+   BUILD_BUG_ON(OPEN_TREE_CLOEXEC != O_CLOEXEC);

Why do we need OPEN_TREE_CLOEXEC?  Wouldn't we be better off just making
the fd returned by open_tree implicitly close-on-exec?  I can think of
no good reason for these file descriptors to be inherited across exec()

How are they different from any file descriptor?  It's not as if it was
something usable only for mounting stuff - again, you can use them
with any ...at() syscalls.

Defaulting to close on exec helps keep out clutter from the API.

Is there a disadvantage to needing an explicit fcntl(F_SETFD) call to
disable close on exec?

Thanks,
Miklos