linux-kernel - [PATCH] chmod.2: document fchmodat(AT_EMPTY

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Message-Id: <20250619-fchmod-empty-path-v1-1-feff2c63abe4@cyphar.com>
Date: Thu, 19 Jun 2025 04:34:30 +1000
From: Aleksa Sarai <cyphar@...har.com>
To: Alejandro Colomar <alx@...nel.org>
Cc: linux-man@...r.kernel.org, Alexey Gladkov <legion@...nel.org>, 
 Christian Brauner <brauner@...nel.org>, linux-fsdevel@...r.kernel.org, 
 linux-kernel@...r.kernel.org, Aleksa Sarai <cyphar@...har.com>
Subject: [PATCH] chmod.2: document fchmodat(AT_EMPTY_PATH)

The documentation and behaviour is indentical to the equivalent flag for
fchownat(2).

Signed-off-by: Aleksa Sarai <cyphar@...har.com>
---
This was added back in 2023, but I forgot to send the documentation
patch for this and only noticed when I was trying to use it and realised
it wasn't in the man page -- mea culpa!
---
 man/man2/chmod.2 | 25 ++++++++++++++++++++++++-
 1 file changed, 24 insertions(+), 1 deletion(-)

diff --git a/man/man2/chmod.2 b/man/man2/chmod.2
index 307589481593..671e256ba525 100644
--- a/man/man2/chmod.2
+++ b/man/man2/chmod.2
@@ -190,7 +190,30 @@ is absolute, then
 is ignored.
 .P
 .I flags
-can either be 0, or include the following flag:
+can either be 0, or include the following flags:
+.TP
+.BR AT_EMPTY_PATH " (since Linux 6.6)"
+.\" commit 5daeb41a6fc9d0d81cb2291884b7410e062d8fa1
+If
+.I path
+is an empty string, operate on the file referred to by
+.I dirfd
+(which may have been obtained using the
+.BR open (2)
+.B O_PATH
+flag).
+In this case,
+.I dirfd
+can refer to any type of file, not just a directory.
+If
+.I dirfd
+is
+.BR AT_FDCWD ,
+the call operates on the current working directory.
+This flag is Linux-specific; define
+.B _GNU_SOURCE
+.\" Before glibc 2.16, defining _ATFILE_SOURCE sufficed
+to obtain its definition.
 .TP
 .B AT_SYMLINK_NOFOLLOW
 If

---
base-commit: 471c38fb3c5c53c6df2fad4a7353559b330c1323
change-id: 20250619-fchmod-empty-path-7680e8bb5481

Best regards,
-- 
Aleksa Sarai <cyphar@...har.com>