[PATCH 07/14] d_path: lift -ENAMETOOLONG handling into callers of prepend_path()

Al Viro
2021-05-19T00:51:20Z

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