git: fae33d1d12a5 - main - open.2: add a note about conversion of a file descriptor into O_PATH

The branch main has been updated by kib:

URL: https://cgit.FreeBSD.org/src/commit/?id=fae33d1d12a51ca2bbdc7f5f189f7a4362fb48f7

commit fae33d1d12a51ca2bbdc7f5f189f7a4362fb48f7
Author:     Konstantin Belousov <kib@FreeBSD.org>
AuthorDate: 2025-05-25 16:32:34 +0000
Commit:     Konstantin Belousov <kib@FreeBSD.org>
CommitDate: 2025-05-25 20:32:26 +0000

    open.2: add a note about conversion of a file descriptor into O_PATH
    
    Reviewed by:    markj
    Sponsored by:   The FreeBSD Foundation
    MFC after:      3 days
    Differential revision:  https://reviews.freebsd.org/D50511
---
 lib/libsys/open.2 | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/lib/libsys/open.2 b/lib/libsys/open.2
index d8540637b690..6200723ed85c 100644
--- a/lib/libsys/open.2
+++ b/lib/libsys/open.2
@@ -464,6 +464,13 @@ flag for
 .Xr fstatat 2
 and related syscalls.
 .Pp
+Conversely, a file descriptor
+.Dv fd
+referencing a filesystem file can be converted to the
+.Dv O_PATH
+type of descriptor by using the following call
+.Dl opath_fd = openat(fd, \[dq]\[dq], O_EMPTY_PATH | O_PATH);
+.Pp
 If successful,
 .Fn open
 returns a non-negative integer, termed a file descriptor.