| Message ID | 20210226224938.18166-1-laurent.pinchart@ideasonboard.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [1/2] list: Add list_is_null() to check if a list_head has been initialized | expand |
Hello! On 27.02.2021 1:49, Laurent Pinchart wrote: > From: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com> > > The new function checks if the list_head prev and next pointers are > NULL, in order to see if a list_head that has been zeroed when allocated > has been initialized with INIT_LIST_HEAD() or added to a list. So zeroed or initialized/added? :-) > This can be used in cleanup functions that want to support being safely > called when an object has not been initialized, to return immediately. > In most cases other fields of the object can be checked for this > purpose, but in some cases a list_head field is the only option. > > Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com> > --- > include/linux/list.h | 13 +++++++++++++ > 1 file changed, 13 insertions(+) > > diff --git a/include/linux/list.h b/include/linux/list.h > index 85c92555e31f..e4fc6954de3b 100644 > --- a/include/linux/list.h > +++ b/include/linux/list.h > @@ -29,6 +29,19 @@ static inline void INIT_LIST_HEAD(struct list_head *list) > list->prev = list; > } > > +/** > + * list_is_null - check if a list_head has been initialized > + * @list: the list > + * > + * Check if the list_head prev and next pointers are NULL. This is useful to > + * see if a list_head that has been zeroed when allocated has been initialized > + * with INIT_LIST_HEAD() or added to a list. So zeroed or initialized/added? :-) > + */ > +static inline bool list_is_null(struct list_head *list) > +{ > + return list->prev == NULL && list->next == NULL; Maybe instead: return !list->prev && !list->next; [...] MBR, Sergei
Hi Laurent, Thanks for the patch. On Sat, Feb 27, 2021 at 12:49:37AM +0200, Laurent Pinchart wrote: > From: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com> > > The new function checks if the list_head prev and next pointers are > NULL, in order to see if a list_head that has been zeroed when allocated > has been initialized with INIT_LIST_HEAD() or added to a list. > > This can be used in cleanup functions that want to support being safely > called when an object has not been initialized, to return immediately. > In most cases other fields of the object can be checked for this > purpose, but in some cases a list_head field is the only option. > > Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com> > --- > include/linux/list.h | 13 +++++++++++++ > 1 file changed, 13 insertions(+) > > diff --git a/include/linux/list.h b/include/linux/list.h > index 85c92555e31f..e4fc6954de3b 100644 > --- a/include/linux/list.h > +++ b/include/linux/list.h > @@ -29,6 +29,19 @@ static inline void INIT_LIST_HEAD(struct list_head *list) > list->prev = list; > } > > +/** > + * list_is_null - check if a list_head has been initialized > + * @list: the list > + * > + * Check if the list_head prev and next pointers are NULL. This is useful to > + * see if a list_head that has been zeroed when allocated has been initialized > + * with INIT_LIST_HEAD() or added to a list. How this should work with an entry that has been removed from a list with list_del()? The values will be LIST_POISON[12] and so this function will return true. Should it return false instead? > + */ > +static inline bool list_is_null(struct list_head *list) > +{ > + return list->prev == NULL && list->next == NULL; What would you think of issuing a warning if one is NULL but the other one isn't? That could happen if the memory is uninitialised by the caller. It should return true in that case, too. > +} > + > #ifdef CONFIG_DEBUG_LIST > extern bool __list_add_valid(struct list_head *new, > struct list_head *prev,
diff --git a/include/linux/list.h b/include/linux/list.h index 85c92555e31f..e4fc6954de3b 100644 --- a/include/linux/list.h +++ b/include/linux/list.h @@ -29,6 +29,19 @@ static inline void INIT_LIST_HEAD(struct list_head *list) list->prev = list; } +/** + * list_is_null - check if a list_head has been initialized + * @list: the list + * + * Check if the list_head prev and next pointers are NULL. This is useful to + * see if a list_head that has been zeroed when allocated has been initialized + * with INIT_LIST_HEAD() or added to a list. + */ +static inline bool list_is_null(struct list_head *list) +{ + return list->prev == NULL && list->next == NULL; +} + #ifdef CONFIG_DEBUG_LIST extern bool __list_add_valid(struct list_head *new, struct list_head *prev,