Em Mon, Sep 22, 2008 at 09:21:53AM +0200, Gerrit Renker escreveu:

quoted text
> This patch prepares for the new and extended feature-negotiation routines.

>

> The following feature-negotiation data structures are provided:

> 	* a container for the various (SP or NN) values,

> 	* symbolic state names to track feature states,

> 	* an entry struct which holds all current information together,

> 	* elementary functions to fill in and process these structures.

>

> Entry structs are arranged as FIFO for the following reason: RFC 4340 specifies

> that if multiple options of the same type are present, they are processed in the

> order of their appearance in the packet; which means that this order needs to be

> preserved in the local data structure (the later insertion code also respects

> this order).

>

> The struct list_head has been chosen for the following reasons: the most

> frequent operations are

>  * add new entry at tail (when receiving Change or setting socket options);

>  * delete entry (when Confirm has been received);

>  * deep copy of entire list (cloning from listening socket onto request socket).

>

> The NN value has been set to 64 bit, which is a currently sufficient upper limit

> (Sequence Window feature has 48 bit).

>

> Signed-off-by: Gerrit Renker

> Acked-by: Ian McDonald

> ---

>  net/dccp/feat.c |   14 ++++++++++++

>  net/dccp/feat.h |   60 +++++++++++++++++++++++++++++++++++++++++++++++++++++++

>  2 files changed, 74 insertions(+), 0 deletions(-)

>

> --- a/net/dccp/feat.c

> +++ b/net/dccp/feat.c

> @@ -23,6 +23,20 @@

>

>  #define DCCP_FEAT_SP_NOAGREE (-123)

>

> +/* copy constructor, fval must not already contain allocated memory */

> +static int dccp_feat_clone_sp_val(dccp_feat_val *fval, u8 const *val, u8 len)

> +{

> +	fval->sp.len = len;

> +	if (fval->sp.len > 0) {

> +		fval->sp.vec = kmemdup(val, len, gfp_any());

> +		if (fval->sp.vec == NULL) {

> +			fval->sp.len = 0;

> +			return -ENOBUFS;

> +		}

> +	}

> +	return 0;

> +}

> +

>  int dccp_feat_change(struct dccp_minisock *dmsk, u8 type, u8 feature,

>  		     u8 *val, u8 len, gfp_t gfp)

>  {

> --- a/net/dccp/feat.h

> +++ b/net/dccp/feat.h

> @@ -14,6 +14,66 @@

>  #include

>  #include "dccp.h"

>

> +enum dccp_feat_type {

> +	FEAT_AT_RX   = 1,	/* located at RX side of half-connection  */

> +	FEAT_AT_TX   = 2,	/* located at TX side of half-connection  */

> +	FEAT_SP      = 4,	/* server-priority reconciliation (6.3.1) */

> +	FEAT_NN	     = 8,	/* non-negotiable reconciliation (6.3.2)  */

> +	FEAT_UNKNOWN = 0xFF	/* not understood or invalid feature	  */

> +};

> +

> +enum dccp_feat_state {

> +	FEAT_DEFAULT = 0,	/* using default values from 6.4 */

> +	FEAT_INITIALISING,	/* feature is being initialised  */

> +	FEAT_CHANGING,		/* Change sent but not confirmed yet */

> +	FEAT_UNSTABLE,		/* local modification in state CHANGING */

> +	FEAT_STABLE		/* both ends (think they) agree */

> +};

> +

> +/**

> + * dccp_feat_val  -  Container for SP or NN feature values

> + * @nn:     single NN value

> + * @sp.vec: single SP value plus optional preference list

> + * @sp.len: length of @sp.vec in bytes

> + */

> +typedef union {

> +	u64 nn;

> +	struct {

> +		u8	*vec;

> +		u8	len;

> +	}   sp;

> +} dccp_feat_val;

> +

> +/**

> + * struct feat_entry  -  Data structure to perform feature negotiation

> + * @feat_num: one of %dccp_feature_numbers

> + * @val: feature's current value (SP features may have preference list)

> + * @state: feature's current state

> + * @needs_mandatory: whether Mandatory options should be sent

> + * @needs_confirm: whether to send a Confirm instead of a Change

> + * @empty_confirm: whether to send an empty Confirm (depends on @needs_confirm)

> + * @is_local: feature location (1) or feature-remote (0)

> + * @node: list pointers, entries arranged in FIFO order

> + */

> +struct dccp_feat_entry {

> +	u8                      feat_num;

> +	dccp_feat_val           val;

> +	enum dccp_feat_state    state:8;

> +	bool			needs_mandatory:1,

> +				needs_confirm:1,

> +				empty_confirm:1,

> +				is_local:1;

> +

> +	struct list_head	node;

> +};

As above:
[acme@doppio ~]$ pahole -C dccp_feat_entry dccp

struct dccp_feat_entry {

	u8                    feat_num;             /*     0     1 */
	/* XXX 7 bytes hole, try to pack */
	dccp_feat_val         val;                  /*     8    16 */

	enum dccp_feat_state  state:8;              /*    24:24  4 */
	/* Bitfield combined with next fields */
	_Bool                 needs_mandatory:1;    /*    25: 7  1 */

	_Bool                 needs_confirm:1;      /*    25: 6  1 */

	_Bool                 empty_confirm:1;      /*    25: 5  1 */

	_Bool                 is_local:1;           /*    25: 4  1 */
	/* XXX 4 bits hole, try to pack */

	/* XXX 6 bytes hole, try to pack */
	struct list_head      node;                 /*    32    16 */
	/* size: 48, cachelines: 1, members: 8 */

	/* sum members: 35, holes: 2, sum holes: 13 */

	/* bit holes: 1, sum bit holes: 4 bits */

	/* last cacheline: 48 bytes */

};
In this case, unless you plan to put more stuff into this struct in the

future, using a bitfield for the bool members is a pessimization, as we

will use the same amount of memory and generate more complex code. So I

suggest:
struct dccp_feat_entry {

	dccp_feat_val         val;                  /*     0    16 */

	enum dccp_feat_state  state:8;              /*    16:24  4 */
	/* Bitfield combined with next fields */
	u8                    feat_num;             /*    17     1 */

	_Bool                 needs_mandatory;      /*    18     1 */

	_Bool                 needs_confirm;        /*    19     1 */

	_Bool                 empty_confirm;        /*    20     1 */

	_Bool                 is_local;             /*    21     1 */
	/* XXX 2 bytes hole, try to pack */
	struct list_head      node;                 /*    24    16 */
	/* size: 40, cachelines: 1, members: 8 */

	/* sum members: 38, holes: 1, sum holes: 2 */

	/* last cacheline: 40 bytes */

};
- Arnaldo

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