linux-kernel - [PATCH] fs: add porting notes about readlink

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Message-ID: <20260203130032.315177-1-mjguzik@gmail.com>
Date: Tue,  3 Feb 2026 14:00:31 +0100
From: Mateusz Guzik <mjguzik@...il.com>
To: viro@...iv.linux.org.uk
Cc: brauner@...nel.org,
	jack@...e.cz,
	linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org,
	Mateusz Guzik <mjguzik@...il.com>
Subject: [PATCH] fs: add porting notes about readlink_copy()

Calling convention has changed in  ea382199071931d1 ("vfs: support caching symlink lengths in inodes")

Signed-off-by: Mateusz Guzik <mjguzik@...il.com>
---
 Documentation/filesystems/porting.rst | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/Documentation/filesystems/porting.rst b/Documentation/filesystems/porting.rst
index 3397937ed838..bd4128ccbb67 100644
--- a/Documentation/filesystems/porting.rst
+++ b/Documentation/filesystems/porting.rst
@@ -1334,3 +1334,13 @@ end_creating() and the parent will be unlocked precisely when necessary.
 
 kill_litter_super() is gone; convert to DCACHE_PERSISTENT use (as all
 in-tree filesystems have done).
+
+---
+
+**mandatory**
+
+readlink_copy() now requires link length as the 4th argument. Said length needs
+to match what strlen() would return if it was ran on the string.
+
+However, if the string is freely accessible for the duration of inode's
+lifetime, consider using inode_set_cached_link() instead.
-- 
2.43.0