[PATCH 02/14] d_path: saner calling conventions for __dentry_path()

Al Viro
2021-05-19T00:51:25Z

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