linux-kernel - [PATCH RFC 2/4] fs: add a kerneldoc header over lookup

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Message-Id: <20240802-openfast-v1-2-a1cff2a33063@kernel.org>
Date: Fri, 02 Aug 2024 17:45:03 -0400
From: Jeff Layton <jlayton@...nel.org>
To: Alexander Viro <viro@...iv.linux.org.uk>, 
 Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>, 
 Andrew Morton <akpm@...ux-foundation.org>
Cc: Josef Bacik <josef@...icpanda.com>, linux-fsdevel@...r.kernel.org, 
 linux-kernel@...r.kernel.org, Jeff Layton <jlayton@...nel.org>
Subject: [PATCH RFC 2/4] fs: add a kerneldoc header over lookup_fast

The lookup_fast helper in fs/namei.c has some subtlety in how dentries
are returned. Document them.

Signed-off-by: Jeff Layton <jlayton@...nel.org>
---
 fs/namei.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/fs/namei.c b/fs/namei.c
index 1e05a0f3f04d..b9bdb8e6214a 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -1613,6 +1613,20 @@ struct dentry *lookup_one_qstr_excl(const struct qstr *name,
 }
 EXPORT_SYMBOL(lookup_one_qstr_excl);
 
+/**
+ * lookup_fast - do fast lockless (but racy) lookup of a dentry
+ * @nd: current nameidata
+ *
+ * Do a fast, but racy lookup in the dcache for the given dentry, and
+ * revalidate it. Returns a valid dentry pointer or NULL if one wasn't
+ * found. On error, an ERR_PTR will be returned.
+ *
+ * If this function returns a valid dentry and the walk is no longer
+ * lazy, the dentry will carry a reference that must later be put. If
+ * RCU mode is still in force, then this is not the case and the dentry
+ * must be legitimized before use. If this returns NULL, then the walk
+ * will no longer be in RCU mode.
+ */
 static struct dentry *lookup_fast(struct nameidata *nd)
 {
 	struct dentry *dentry, *parent = nd->path.dentry;

-- 
2.45.2