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>

diff --git a/fs/d_path.c b/fs/d_path.c
index 72b8087..327cc37 100644 (file)
--- a/fs/d_path.c
+++ b/fs/d_path.c
@@ -127,8 +127,7 @@ restart:
                }
                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 @@ restart:
        }
        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);