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From:   Al Viro <viro@ZenIV.linux.org.uk>
To:     linux-fsdevel@vger.kernel.org
Cc:     Linus Torvalds <torvalds@linux-foundation.org>,
        linux-kernel@vger.kernel.org, Aleksa Sarai <cyphar@cyphar.com>,
        David Howells <dhowells@redhat.com>,
        Eric Biederman <ebiederm@xmission.com>,
        Christian Brauner <christian.brauner@ubuntu.com>,
        Al Viro <viro@zeniv.linux.org.uk>
Subject: [PATCH 1/9] merging pick_link() with get_link(), part 1
Date:   Sun, 19 Jan 2020 03:17:30 +0000
Message-Id: <20200119031738.2681033-18-viro@ZenIV.linux.org.uk>
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 <20200119031738.2681033-1-viro@ZenIV.linux.org.uk>
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From: Al Viro <viro@zeniv.linux.org.uk>

Move restoring LOOKUP_PARENT and zeroing nd->stack.name[0] past
the call of get_link() (nothing _currently_ uses them in there).
That allows to moved the call of may_follow_link() into get_link()
as well, since now the presence of LOOKUP_PARENT distinguishes
the callers from each other (link_path_walk() has it, trailing_symlink()
doesn't).

Preparations for folding trailing_symlink() into callers (lookup_last()
and do_last()) and changing the calling conventions of those.  Next
stage after that will have get_link() call migrate into walk_component(),
then - into step_into().  It's tricky enough to warrant doing that
in stages, unfortunately...

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
---
 fs/namei.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/fs/namei.c b/fs/namei.c
index f9fa8579cf6a..45cedbe267ab 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -1114,6 +1114,12 @@ const char *get_link(struct nameidata *nd)
 	int error;
 	const char *res;
 
+	if (!(nd->flags & LOOKUP_PARENT)) {
+		error = may_follow_link(nd);
+		if (unlikely(error))
+			return ERR_PTR(error);
+	}
+
 	if (unlikely(nd->flags & LOOKUP_NO_SYMLINKS))
 		return ERR_PTR(-ELOOP);
 
@@ -2328,13 +2334,9 @@ static const char *path_init(struct nameidata *nd, unsigned flags)
 
 static const char *trailing_symlink(struct nameidata *nd)
 {
-	const char *s;
-	int error = may_follow_link(nd);
-	if (unlikely(error))
-		return ERR_PTR(error);
+	const char *s = get_link(nd);
 	nd->flags |= LOOKUP_PARENT;
 	nd->stack[0].name = NULL;
-	s = get_link(nd);
 	return s ? s : "";
 }
 
-- 
2.20.1