| Message ID | 20201027221916.463235-1-arnd@kernel.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v3] seq_file: fix clang warning for NULL pointer arithmetic | expand |
> +#define SEQ_OPEN_SINGLE (void *)1 I still think a comment explaining the magic value here would be useful. Otherwise this looks good: Reviewed-by: Christoph Hellwig <hch@lst.de>
On Tue, Oct 27, 2020 at 11:18:24PM +0100, Arnd Bergmann wrote: > From: Arnd Bergmann <arnd@arndb.de> > > Clang points out that adding something to NULL is notallowed not allowed > 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 code to be extra explicit about the valid, giving valid what? > them named SEQ_OPEN_EOF and SEQ_OPEN_SINGLE definitions. > 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 <arnd@arndb.de> Aside from the minor nits in the commit message, this should keep the same behavior while eliminating the warning and making it a little easier to understand. Reviewed-by: Nathan Chancellor <natechancellor@gmail.com> > --- > v2: add the named macros after Christoph Hellwig pointed out > that my original logic was too ugly. > Suggestions for better names welcome > > v3: don't overload the NULL return, avoid ?: operator > --- > fs/kernfs/file.c | 9 ++++++--- > fs/seq_file.c | 5 ++++- > include/linux/seq_file.h | 2 ++ > 3 files changed, 12 insertions(+), 4 deletions(-) > > diff --git a/fs/kernfs/file.c b/fs/kernfs/file.c > index f277d023ebcd..5a5adb03c6df 100644 > --- a/fs/kernfs/file.c > +++ b/fs/kernfs/file.c > @@ -121,10 +121,13 @@ static void *kernfs_seq_start(struct seq_file *sf, loff_t *ppos) > return next; > } else { > /* > - * The same behavior and code as single_open(). Returns > - * !NULL if pos is at the beginning; otherwise, NULL. > + * The same behavior and code as single_open(). Continues > + * if pos is at the beginning; otherwise, NULL. > */ > - return NULL + !*ppos; > + if (*ppos) > + return NULL; > + > + return SEQ_OPEN_SINGLE; > } > } > > diff --git a/fs/seq_file.c b/fs/seq_file.c > index 31219c1db17d..6b467d769501 100644 > --- a/fs/seq_file.c > +++ b/fs/seq_file.c > @@ -526,7 +526,10 @@ EXPORT_SYMBOL(seq_dentry); > > static void *single_start(struct seq_file *p, loff_t *pos) > { > - return NULL + (*pos == 0); > + if (*pos) > + return NULL; > + > + return SEQ_OPEN_SINGLE; > } > > 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 813614d4b71f..eb344448d4da 100644 > --- a/include/linux/seq_file.h > +++ b/include/linux/seq_file.h > @@ -37,6 +37,8 @@ struct seq_operations { > > #define SEQ_SKIP 1 > > +#define SEQ_OPEN_SINGLE (void *)1 > + > /** > * seq_has_overflowed - check if the buffer has overflowed > * @m: the seq_file handle > -- > 2.27.0 >
diff --git a/fs/kernfs/file.c b/fs/kernfs/file.c index f277d023ebcd..5a5adb03c6df 100644 --- a/fs/kernfs/file.c +++ b/fs/kernfs/file.c @@ -121,10 +121,13 @@ static void *kernfs_seq_start(struct seq_file *sf, loff_t *ppos) return next; } else { /* - * The same behavior and code as single_open(). Returns - * !NULL if pos is at the beginning; otherwise, NULL. + * The same behavior and code as single_open(). Continues + * if pos is at the beginning; otherwise, NULL. */ - return NULL + !*ppos; + if (*ppos) + return NULL; + + return SEQ_OPEN_SINGLE; } } diff --git a/fs/seq_file.c b/fs/seq_file.c index 31219c1db17d..6b467d769501 100644 --- a/fs/seq_file.c +++ b/fs/seq_file.c @@ -526,7 +526,10 @@ EXPORT_SYMBOL(seq_dentry); static void *single_start(struct seq_file *p, loff_t *pos) { - return NULL + (*pos == 0); + if (*pos) + return NULL; + + return SEQ_OPEN_SINGLE; } 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 813614d4b71f..eb344448d4da 100644 --- a/include/linux/seq_file.h +++ b/include/linux/seq_file.h @@ -37,6 +37,8 @@ struct seq_operations { #define SEQ_SKIP 1 +#define SEQ_OPEN_SINGLE (void *)1 + /** * seq_has_overflowed - check if the buffer has overflowed * @m: the seq_file handle