On Tue, May 13, 2025 at 3:18 PM Jan Kara <jack@xxxxxxx> wrote:
>
> We use flex array 'buf' in fanotify_fh to contain the file handle
> content. However the buffer is not a proper flex array. It has a
> preconfigured fixed size. Furthermore if fixed size is not big enough,
> we use external separately allocated buffer. Hence don't pretend buf is
> a flex array since we have to use special accessors anyway and instead
> just modify the accessors to do the pointer math without flex array.
> This fixes warnings that flex array is not the last struct member in
> fanotify_fid_event or fanotify_error_event.
>
> Signed-off-by: Jan Kara <jack@xxxxxxx>
Makes sense.
Reviewed-by: Amir Goldstein <amir73il@xxxxxxxxx>
> ---
> fs/notify/fanotify/fanotify.c | 2 +-
> fs/notify/fanotify/fanotify.h | 9 ++++-----
> 2 files changed, 5 insertions(+), 6 deletions(-)
>
> Amir, how about this solution for the flex array warnings?
>
> diff --git a/fs/notify/fanotify/fanotify.c b/fs/notify/fanotify/fanotify.c
> index 6d386080faf2..7bc5580a91dc 100644
> --- a/fs/notify/fanotify/fanotify.c
> +++ b/fs/notify/fanotify/fanotify.c
> @@ -415,7 +415,7 @@ static int fanotify_encode_fh(struct fanotify_fh *fh, struct inode *inode,
> {
> int dwords, type = 0;
> char *ext_buf = NULL;
> - void *buf = fh->buf;
> + void *buf = fh + 1;
> int err;
>
> fh->type = FILEID_ROOT;
> diff --git a/fs/notify/fanotify/fanotify.h b/fs/notify/fanotify/fanotify.h
> index b44e70e44be6..b78308975082 100644
> --- a/fs/notify/fanotify/fanotify.h
> +++ b/fs/notify/fanotify/fanotify.h
> @@ -25,7 +25,7 @@ enum {
> * stored in either the first or last 2 dwords.
> */
> #define FANOTIFY_INLINE_FH_LEN (3 << 2)
> -#define FANOTIFY_FH_HDR_LEN offsetof(struct fanotify_fh, buf)
> +#define FANOTIFY_FH_HDR_LEN sizeof(struct fanotify_fh)
>
> /* Fixed size struct for file handle */
> struct fanotify_fh {
> @@ -34,7 +34,6 @@ struct fanotify_fh {
> #define FANOTIFY_FH_FLAG_EXT_BUF 1
> u8 flags;
> u8 pad;
> - unsigned char buf[];
> } __aligned(4);
>
> /* Variable size struct for dir file handle + child file handle + name */
> @@ -92,7 +91,7 @@ static inline char **fanotify_fh_ext_buf_ptr(struct fanotify_fh *fh)
> BUILD_BUG_ON(FANOTIFY_FH_HDR_LEN % 4);
> BUILD_BUG_ON(__alignof__(char *) - 4 + sizeof(char *) >
> FANOTIFY_INLINE_FH_LEN);
> - return (char **)ALIGN((unsigned long)(fh->buf), __alignof__(char *));
> + return (char **)ALIGN((unsigned long)(fh + 1), __alignof__(char *));
> }
>
> static inline void *fanotify_fh_ext_buf(struct fanotify_fh *fh)
> @@ -102,7 +101,7 @@ static inline void *fanotify_fh_ext_buf(struct fanotify_fh *fh)
>
> static inline void *fanotify_fh_buf(struct fanotify_fh *fh)
> {
> - return fanotify_fh_has_ext_buf(fh) ? fanotify_fh_ext_buf(fh) : fh->buf;
> + return fanotify_fh_has_ext_buf(fh) ? fanotify_fh_ext_buf(fh) : fh + 1;
> }
>
> static inline int fanotify_info_dir_fh_len(struct fanotify_info *info)
> @@ -278,7 +277,7 @@ static inline void fanotify_init_event(struct fanotify_event *event,
> #define FANOTIFY_INLINE_FH(name, size) \
> struct { \
> struct fanotify_fh name; \
> - /* Space for object_fh.buf[] - access with fanotify_fh_buf() */ \
> + /* Space for filehandle - access with fanotify_fh_buf() */ \
> unsigned char _inline_fh_buf[size]; \
> }
>
> --
> 2.43.0
>
