Re: [PATCH 2/3] can: raw: use bitfields to store flags in struct raw_sock

[Christophe JAILLET]

Le 15/09/2025 à 11:23, Vincent Mailhol a écrit :
> The loopback, recv_own_msgs, fd_frames and xl_frames fields of struct
> raw_sock just need to store one bit of information.
>
> Declare all those members as a bitfields of type unsigned int and
> width one bit.
>
> Add a temporary variable to raw_setsockopt() and raw_getsockopt() to
> make the conversion between the stored bits and the socket interface.
>
> This reduces struct raw_sock by eight bytes.
>
> Statistics before:
>
>    $ pahole --class_name=raw_sock net/can/raw.o
>    struct raw_sock {
>    	struct sock                sk __attribute__((__aligned__(8))); /*     0   776 */
>
>    	/* XXX last struct has 1 bit hole */
>
>    	/* --- cacheline 12 boundary (768 bytes) was 8 bytes ago --- */
>    	int                        bound;                /*   776     4 */
>    	int                        ifindex;              /*   780     4 */
>    	struct net_device *        dev;                  /*   784     8 */
>    	netdevice_tracker          dev_tracker;          /*   792     0 */
>    	struct list_head           notifier;             /*   792    16 */
>    	int                        loopback;             /*   808     4 */
>    	int                        recv_own_msgs;        /*   812     4 */
>    	int                        fd_frames;            /*   816     4 */
>    	int                        xl_frames;            /*   820     4 */
>    	struct can_raw_vcid_options raw_vcid_opts;       /*   824     4 */
>    	canid_t                    tx_vcid_shifted;      /*   828     4 */
>    	/* --- cacheline 13 boundary (832 bytes) --- */
>    	canid_t                    rx_vcid_shifted;      /*   832     4 */
>    	canid_t                    rx_vcid_mask_shifted; /*   836     4 */
>    	int                        join_filters;         /*   840     4 */
>    	int                        count;                /*   844     4 */
>    	struct can_filter          dfilter;              /*   848     8 */
>    	struct can_filter *        filter;               /*   856     8 */
>    	can_err_mask_t             err_mask;             /*   864     4 */
>
>    	/* XXX 4 bytes hole, try to pack */
>
>    	struct uniqframe *         uniq;                 /*   872     8 */
>
>    	/* size: 880, cachelines: 14, members: 20 */
>    	/* sum members: 876, holes: 1, sum holes: 4 */
>    	/* member types with bit holes: 1, total: 1 */
>    	/* forced alignments: 1 */
>    	/* last cacheline: 48 bytes */
>    } __attribute__((__aligned__(8)));
>
> ...and after:
>
>    $ pahole --class_name=raw_sock net/can/raw.o
>    struct raw_sock {
>    	struct sock                sk __attribute__((__aligned__(8))); /*     0   776 */
>
>    	/* XXX last struct has 1 bit hole */
>
>    	/* --- cacheline 12 boundary (768 bytes) was 8 bytes ago --- */
>    	int                        bound;                /*   776     4 */
>    	int                        ifindex;              /*   780     4 */
>    	struct net_device *        dev;                  /*   784     8 */
>    	netdevice_tracker          dev_tracker;          /*   792     0 */
>    	struct list_head           notifier;             /*   792    16 */
>    	unsigned int               loopback:1;           /*   808: 0  4 */
>    	unsigned int               recv_own_msgs:1;      /*   808: 1  4 */
>    	unsigned int               fd_frames:1;          /*   808: 2  4 */
>    	unsigned int               xl_frames:1;          /*   808: 3  4 */
>
>    	/* XXX 4 bits hole, try to pack */
>    	/* Bitfield combined with next fields */
>
>    	struct can_raw_vcid_options raw_vcid_opts;       /*   809     4 */
>
>    	/* XXX 3 bytes hole, try to pack */
>
>    	canid_t                    tx_vcid_shifted;      /*   816     4 */
>    	canid_t                    rx_vcid_shifted;      /*   820     4 */
>    	canid_t                    rx_vcid_mask_shifted; /*   824     4 */
>    	int                        join_filters;         /*   828     4 */
>    	/* --- cacheline 13 boundary (832 bytes) --- */
>    	int                        count;                /*   832     4 */
>    	struct can_filter          dfilter;              /*   836     8 */
>
>    	/* XXX 4 bytes hole, try to pack */
>
>    	struct can_filter *        filter;               /*   848     8 */
>    	can_err_mask_t             err_mask;             /*   856     4 */
>
>    	/* XXX 4 bytes hole, try to pack */
>
>    	struct uniqframe *         uniq;                 /*   864     8 */
>
>    	/* size: 872, cachelines: 14, members: 20 */
>    	/* sum members: 860, holes: 3, sum holes: 11 */
>    	/* sum bitfield members: 4 bits, bit holes: 1, sum bit holes: 4 bits */
>    	/* member types with bit holes: 1, total: 1 */
>    	/* forced alignments: 1 */
>    	/* last cacheline: 40 bytes */
>    } __attribute__((__aligned__(8)));
>
> Signed-off-by: Vincent Mailhol <mailhol@xxxxxxxxxx>
> ---
>   net/can/raw.c | 47 ++++++++++++++++++++++++++++-------------------
>   1 file changed, 28 insertions(+), 19 deletions(-)
>
> diff --git a/net/can/raw.c b/net/can/raw.c
> index db21d8a8c54d1b6a25a72c7a9d11d5c94f3187b5..cec580ecd58e36931d1be05716e6beb9c93aa271 100644
> --- a/net/can/raw.c
> +++ b/net/can/raw.c
> @@ -87,10 +87,10 @@ struct raw_sock {
>   	struct net_device *dev;
>   	netdevice_tracker dev_tracker;
>   	struct list_head notifier;
> -	int loopback;
> -	int recv_own_msgs;
> -	int fd_frames;
> -	int xl_frames;
> +	unsigned int loopback:1;
> +	unsigned int recv_own_msgs:1;
> +	unsigned int fd_frames:1;
> +	unsigned int xl_frames:1;
>   	struct can_raw_vcid_options raw_vcid_opts;
>   	canid_t tx_vcid_shifted;
>   	canid_t rx_vcid_shifted;

[...]

Hi,

just in case, it looks like bound and join_filters could also be defined 
in the bitfield.

just my 2c.

CJ