-----Original Message-----
From: Al Viro <redacted> On Behalf Of Al Viro
Sent: Wednesday, May 19, 2021 8:49 AM
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Justin He <redacted>; Petr Mladek <pmladek@suse.com>; Steven
Rostedt [off-list ref]; Sergey Senozhatsky
[off-list ref]; Andy Shevchenko
[off-list ref]; Rasmus Villemoes
[off-list ref]; Jonathan Corbet [off-list ref]; Heiko
Carstens [off-list ref]; Vasily Gorbik [off-list ref]; Christian
Borntraeger [off-list ref]; Eric W . Biederman
[off-list ref]; Darrick J. Wong [off-list ref]; Peter
Zijlstra (Intel) [off-list ref]; Ira Weiny [off-list ref];
Eric Biggers [off-list ref]; Ahmed S. Darwish
[off-list ref]; open list:DOCUMENTATION <linux-
doc@vger.kernel.org>; Linux Kernel Mailing List <linux-
kernel@vger.kernel.org>; linux-s390 [off-list ref]; linux-
fsdevel [off-list ref]
Subject: [PATCH 07/14] d_path: lift -ENAMETOOLONG handling into callers of
prepend_path()

The only negative value ever returned by prepend_path() is -ENAMETOOLONG
and callers can recognize that situation (overflow) by looking at the
sign of buflen.  Lift that into the callers; we already have the
same logics (buf if buflen is non-negative, ERR_PTR(-ENAMETOOLONG)
otherwise)
in several places and that'll become a new primitive several commits down
the road.

Make prepend_path() return 0 instead of -ENAMETOOLONG.  That makes for
saner calling conventions (0/1/2/3/-ENAMETOOLONG is obnoxious) and
callers actually get simpler, especially once the aforementioned
primitive gets added.

In prepend_path() itself we switch prepending the / (in case of
empty path) to use of prepend() - no need to open-code that, compiler
will do the right thing.  It's exactly the same logics as in
__dentry_path().

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
---
 fs/d_path.c | 39 +++++++++++----------------------------
 1 file changed, 11 insertions(+), 28 deletions(-)

diff --git a/fs/d_path.c b/fs/d_path.c
index 72b8087aaf9c..327cc3744554 100644
--- a/fs/d_path.c
+++ b/fs/d_path.c

@@ -127,8 +127,7 @@ static int prepend_path(const struct path *path,
              }
              parent = dentry->d_parent;
              prefetch(parent);
-             error = prepend_name(&bptr, &blen, &dentry->d_name);
-             if (error)
+             if (unlikely(prepend_name(&bptr, &blen, &dentry->d_name) < 0))
                      break;

              dentry = parent;

@@ -149,12 +148,9 @@ static int prepend_path(const struct path *path,
      }
      done_seqretry(&mount_lock, m_seq);

-     if (error >= 0 && bptr == *buffer) {
-             if (--blen < 0)
-                     error = -ENAMETOOLONG;
-             else
-                     *--bptr = '/';
-     }
+     if (blen == *buflen)
+             prepend(&bptr, &blen, "/", 1);
+
      *buffer = bptr;
      *buflen = blen;
      return error;

@@ -181,16 +177,11 @@ char *__d_path(const struct path *path,
             char *buf, int buflen)
 {
      char *res = buf + buflen;
-     int error;

      prepend(&res, &buflen, "", 1);
-     error = prepend_path(path, root, &res, &buflen);
-
-     if (error < 0)
-             return ERR_PTR(error);
-     if (error > 0)
+     if (prepend_path(path, root, &res, &buflen) > 0)
              return NULL;
-     return res;
+     return buflen >= 0 ? res : ERR_PTR(-ENAMETOOLONG);
 }

 char *d_absolute_path(const struct path *path,

@@ -198,16 +189,11 @@ char *d_absolute_path(const struct path *path,
 {
      struct path root = {};
      char *res = buf + buflen;
-     int error;

      prepend(&res, &buflen, "", 1);
-     error = prepend_path(path, &root, &res, &buflen);
-
-     if (error > 1)
-             error = -EINVAL;
-     if (error < 0)
-             return ERR_PTR(error);
-     return res;
+     if (prepend_path(path, &root, &res, &buflen) > 1)
+             return ERR_PTR(-EINVAL);
+     return buflen >= 0 ? res : ERR_PTR(-ENAMETOOLONG);

 }

 static void get_fs_root_rcu(struct fs_struct *fs, struct path *root)

@@ -240,7 +226,6 @@ char *d_path(const struct path *path, char *buf, int

buflen)
 {
      char *res = buf + buflen;
      struct path root;
-     int error;

      /*
       * We have various synthetic filesystems that never get mounted.  On

@@ -263,12 +248,10 @@ char *d_path(const struct path *path, char *buf, int

buflen)
              prepend(&res, &buflen, " (deleted)", 11);
      else
              prepend(&res, &buflen, "", 1);
-     error = prepend_path(path, &root, &res, &buflen);
+     prepend_path(path, &root, &res, &buflen);
      rcu_read_unlock();

-     if (error < 0)
-             res = ERR_PTR(error);
-     return res;
+     return buflen >= 0 ? res : ERR_PTR(-ENAMETOOLONG);
 }
 EXPORT_SYMBOL(d_path);

--
2.11.0