-----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-
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fsdevel [off-list ref]
Subject: [PATCH 02/14] d_path: saner calling conventions for __dentry_path()

1) lift NUL-termination into the callers
2) pass pointer to the end of buffer instead of that to beginning.

(1) allows to simplify dentry_path() - we don't need to play silly
games with restoring the leading / of "//deleted" after __dentry_path()
would've overwritten it with NUL.

We also do not need to check if (either) prepend() in there fails -
if the buffer is not large enough, we'll end with negative buflen
after prepend() and __dentry_path() will return the right value
(ERR_PTR(-ENAMETOOLONG)) just fine.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
---
 fs/d_path.c | 33 +++++++++++++--------------------
 1 file changed, 13 insertions(+), 20 deletions(-)

diff --git a/fs/d_path.c b/fs/d_path.c
index 01df5dfa1f88..1a1cf05e7780 100644
--- a/fs/d_path.c
+++ b/fs/d_path.c

@@ -326,22 +326,21 @@ char *simple_dname(struct dentry *dentry, char

*buffer, int buflen)
 /*
  * Write full pathname from the root of the filesystem into the buffer.
  */

-static char *__dentry_path(const struct dentry *d, char *buf, int buflen)
+static char *__dentry_path(const struct dentry *d, char *p, int buflen)
 {
      const struct dentry *dentry;
      char *end, *retval;
      int len, seq = 0;
      int error = 0;

-     if (buflen < 2)
+     if (buflen < 1)
              goto Elong;

      rcu_read_lock();
 restart:
      dentry = d;
-     end = buf + buflen;
+     end = p;
      len = buflen;
-     prepend(&end, &len, "", 1);
      /* Get '/' right */
      retval = end-1;
      *retval = '/';

@@ -373,27 +372,21 @@ static char *__dentry_path(const struct dentry *d,

char *buf, int buflen)

 char *dentry_path_raw(const struct dentry *dentry, char *buf, int buflen)
 {
-     return __dentry_path(dentry, buf, buflen);
+     char *p = buf + buflen;
+     prepend(&p, &buflen, "", 1);
+     return __dentry_path(dentry, p, buflen);
 }
 EXPORT_SYMBOL(dentry_path_raw);

 char *dentry_path(const struct dentry *dentry, char *buf, int buflen)
 {
-     char *p = NULL;
-     char *retval;
-
-     if (d_unlinked(dentry)) {
-             p = buf + buflen;
-             if (prepend(&p, &buflen, "//deleted", 10) != 0)
-                     goto Elong;
-             buflen++;
-     }
-     retval = __dentry_path(dentry, buf, buflen);
-     if (!IS_ERR(retval) && p)
-             *p = '/';       /* restore '/' overriden with '\0' */
-     return retval;
-Elong:
-     return ERR_PTR(-ENAMETOOLONG);
+     char *p = buf + buflen;
+
+     if (unlikely(d_unlinked(dentry)))
+             prepend(&p, &buflen, "//deleted", 10);
+     else
+             prepend(&p, &buflen, "", 1);
+     return __dentry_path(dentry, p, buflen);
 }

 static void get_fs_root_and_pwd_rcu(struct fs_struct *fs, struct path
*root,
--
2.11.0