Hi Maíra, On Mon, Jan 31, 2022 at 03:22:42PM -0300, Maíra Canal wrote: > 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@xxxxxx> Thanks a lot for the patch! It looks like Arnd sent a similar patch but it was never picked up: https://lore.kernel.org/r/20201028151202.3074398-1-arnd@xxxxxxxxxx/ This is a cleaner solution as it uses existing defines and functions to deduplicate the code. Reviewed-by: Nathan Chancellor <nathan@xxxxxxxxxx> > --- > V1 -> V2: > - Use SEQ_START_TOKEN instead of open-coding it > - kernfs_seq_start call single_start instead of open-coding it > V2 -> V3: > - Remove the EXPORT of the single_start symbol > --- > fs/kernfs/file.c | 7 +------ > fs/seq_file.c | 4 ++-- > include/linux/seq_file.h | 1 + > 3 files changed, 4 insertions(+), 8 deletions(-) > > diff --git a/fs/kernfs/file.c b/fs/kernfs/file.c > index 9414a7a60a9f..7aefaca876a0 100644 > --- 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 f8e1f4ee87ff..7ab8a58c29b6 100644 > --- 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 88cc16444b43..60820ab511d2 100644 > --- 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 *); > -- > 2.34.1 >
