wishlist: mark unlinkat2() as in-progress

Move "Unlinking via two file descriptors" from TODO to In-Progress
next to the related `AT_EMPTY_PATH` for `unlinkat()` entry. Rename
the proposed syscall in the prototype to `unlinkat2()` to match the
"two file descriptors" framing.

Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>

Author: brauner

README.md

@@ -195,6 +195,22 @@ mounts.
 around only a file descriptor without having to keep the path around
 to be able to unlink the file/directory.
 
+### Unlinking via two file descriptors
+
+`unlinkat2(dir_fd, name, inode_fd)`: taking one file descriptor
+for the directory to remove a file in, and another one referring
+to the inode of the filename to remove. This call should only
+succeed if the specified filename still refers to the specified
+inode.
+
+**Use-Case:** code that operates on a well-know path that might be
+shared by multiple programs that jointly manage it might want to
+safely remove a filename under the guarantee it still refers to
+the expected inode. As a specific example, consider lock files,
+that should be cleaned up only if they still refer to the assumed
+owner's instance, but leave the file in place if another process
+already took over the filename.
+
 ### `AT_EMPTY_PATH` support for `openat()` and `openat2()`
 
 To get an operable version of an `O_PATH` file descriptors, it is
@@ -323,22 +339,6 @@ disk I/O. Consider implementation of a naive web browser which is
 pointed to `file://dev/zero`, not expecting an endless amount of
 data to read.
 
-### Unlinking via two file descriptors
-
-`unlinkat3(dir_fd, name, inode_fd)`: taking one file descriptor
-for the directory to remove a file in, and another one referring
-to the inode of the filename to remove. This call should only
-succeed if the specified filename still refers to the specified
-inode.
-
-**Use-Case:** code that operates on a well-know path that might be
-shared by multiple programs that jointly manage it might want to
-safely remove a filename under the guarantee it still refers to
-the expected inode. As a specific example, consider lock files,
-that should be cleaned up only if they still refer to the assumed
-owner's instance, but leave the file in place if another process
-already took over the filename.
-
 ### Determining if a mount point belongs to the current user
 
 Ability to determine if a mount point belongs to the current user