[PATCH] seq_file: fix clang warning for NULL pointer arithmetic

[Arnd Bergmann]

From: Arnd Bergmann <a...@arndb.de>

Clang points out that adding something to NULL is notallowed
in standard C:

fs/kernfs/file.c:127:15: warning: performing pointer arithmetic on a
null pointer has undefined behavior [-Wnull-pointer-arithmetic]
                return NULL + !*ppos;
                       ~~~~ ^
fs/seq_file.c:529:14: warning: performing pointer arithmetic on a
null pointer has undefined behavior [-Wnull-pointer-arithmetic]
        return NULL + (*pos == 0);

Rephrase the function to do the same thing without triggering that
warning. Linux already relies on a specific binary representation
of NULL, so it makes no real difference here. The instance in
kernfs was copied from single_start, so fix both at once.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Fixes: c2b19daf6760 ("sysfs, kernfs: prepare read path for kernfs")
Signed-off-by: Arnd Bergmann <a...@arndb.de>
---
 fs/kernfs/file.c | 2 +-
 fs/seq_file.c    | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/kernfs/file.c b/fs/kernfs/file.c
index f277d023ebcd..b55e6ef4d677 100644
--- a/fs/kernfs/file.c
+++ b/fs/kernfs/file.c
@@ -124,7 +124,7 @@ static void *kernfs_seq_start(struct seq_file *sf, loff_t 
*ppos)
                 * The same behavior and code as single_open().  Returns
                 * !NULL if pos is at the beginning; otherwise, NULL.
                 */
-               return NULL + !*ppos;
+               return (void *)(uintptr_t)!*ppos;
        }
 }
 
diff --git a/fs/seq_file.c b/fs/seq_file.c
index 31219c1db17d..d456468eb934 100644
--- a/fs/seq_file.c
+++ b/fs/seq_file.c
@@ -526,7 +526,7 @@ EXPORT_SYMBOL(seq_dentry);
 
 static void *single_start(struct seq_file *p, loff_t *pos)
 {
-       return NULL + (*pos == 0);
+       return (void *)(uintptr_t)(*pos == 0);
 }
 
 static void *single_next(struct seq_file *p, void *v, loff_t *pos)
-- 
2.27.0