seq_file: fix NULL pointer arithmetic warning

Implement conditional logic in order to replace NULL pointer arithmetic.

The use of NULL pointer arithmetic was pointed out by clang with the
following warning:

fs/kernfs/file.c:128:15: warning: performing pointer arithmetic on a
null pointer has undefined behavior [-Wnull-pointer-arithmetic]
                return NULL + !*ppos;
                       ~~~~ ^
fs/seq_file.c:559:14: warning: performing pointer arithmetic on a
null pointer has undefined behavior [-Wnull-pointer-arithmetic]
        return NULL + (*pos == 0);

Signed-off-by: Maíra Canal <maira.canal@usp.br>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

diff --git a/fs/kernfs/file.c b/fs/kernfs/file.c
index 9414a7a..7aefaca 100644 (file)
--- a/fs/kernfs/file.c
+++ b/fs/kernfs/file.c
@@ -120,13 +120,8 @@ static void *kernfs_seq_start(struct seq_file *sf, loff_t *ppos)
                if (next == ERR_PTR(-ENODEV))
                        kernfs_seq_stop_active(sf, next);
                return next;
-       } else {
-               /*
-                * The same behavior and code as single_open().  Returns
-                * !NULL if pos is at the beginning; otherwise, NULL.
-                */
-               return NULL + !*ppos;
        }
+       return single_start(sf, ppos);
 }
 
 static void *kernfs_seq_next(struct seq_file *sf, void *v, loff_t *ppos)

diff --git a/fs/seq_file.c b/fs/seq_file.c
index f8e1f4e..7ab8a58 100644 (file)
--- a/fs/seq_file.c
+++ b/fs/seq_file.c
@@ -554,9 +554,9 @@ int seq_dentry(struct seq_file *m, struct dentry *dentry, const char *esc)
 }
 EXPORT_SYMBOL(seq_dentry);
 
-static void *single_start(struct seq_file *p, loff_t *pos)
+void *single_start(struct seq_file *p, loff_t *pos)
 {
-       return NULL + (*pos == 0);
+       return *pos ? NULL : SEQ_START_TOKEN;
 }
 
 static void *single_next(struct seq_file *p, void *v, loff_t *pos)

diff --git a/include/linux/seq_file.h b/include/linux/seq_file.h
index 88cc164..60820ab 100644 (file)
--- a/include/linux/seq_file.h
+++ b/include/linux/seq_file.h
@@ -162,6 +162,7 @@ int seq_dentry(struct seq_file *, struct dentry *, const char *);
 int seq_path_root(struct seq_file *m, const struct path *path,
                  const struct path *root, const char *esc);
 
+void *single_start(struct seq_file *, loff_t *);
 int single_open(struct file *, int (*)(struct seq_file *, void *), void *);
 int single_open_size(struct file *, int (*)(struct seq_file *, void *), void *, size_t);
 int single_release(struct inode *, struct file *);