Re: [PATCH v3 1/3] pidfd: allow pidfd_open() on non-thread-group leaders

On 01/26, Christian Brauner wrote:

quoted

--- a/include/uapi/linux/pidfd.h
+++ b/include/uapi/linux/pidfd.h

@@ -7,6 +7,7 @@
 #include <linux/fcntl.h>

 /* Flags for pidfd_open().  */
-#define PIDFD_NONBLOCK O_NONBLOCK
+#define PIDFD_NONBLOCK	O_NONBLOCK
+#define PIDFD_THREAD	O_EXCL	// or anything else not used by anon_inode's

I like it!

The only request I would have is to not alias O_EXCL and PIDFD_THREAD.
Because it doesn't map as clearly as NONBLOCK did.

But it would be nice to have PIDFD_THREAD in file->f_flags. Where else
can we keep it?

I chose O_EXCL because it can only be used at open time, it can never
be used or changed after anon_inode_getfile(), so we can safely do

	pidfd_file->f_flags |= PIDFD_THREAD;

in __pidfd_prepare() and then check in pidfd_poll/pidfd_send_signal.

What do you suggest instead?

Oleg.