Packing netgraph structs

[Ruslan Ermilov]

On Thu, Jul 01, 2004 at 02:00:06PM +0100, Anil Madhavapeddy wrote:
> On 1 Jul 2004, at 13:48, Roman Kurakin wrote:
> >
> >If this is a problem why can't you make some wrapper that will 
> >pack/unpack written on C,
> >which will be a lib for you?
> 
> Because I want to minimise the size of the foreign bindings - this 
> would require C code for every single Netgraph struct.  If they were 
> packed, I could just do it all in OCaml.
> 
> Isn't this a problem for other language bindings as well, or is 
> everyone doing Netgraph userland hacking in C at the moment?
> 
We use Netgraph from within Python, using the netgraph(3) library,
and we pack/unpack various Netgraph related structs just happily.

Speaking of "struct ng_mesg", if you pack it, it will essentially
stay the same, because I believe it was created with this in mind,
as well as most if not all other user-accessible Netgraph structs.

/* A netgraph message */
struct ng_mesg {
        struct  ng_msghdr {
                u_char          version;                /* must == NG_VERSION */
                u_char          spare;                  /* pad to 2 bytes */
                u_int16_t       arglen;                 /* length of data */
                u_int32_t       flags;                  /* message status */
                u_int32_t       token;                  /* match with reply */
                u_int32_t       typecookie;             /* node's type cookie */
                u_int32_t       cmd;                    /* command identifier */
                u_char          cmdstr[NG_CMDSTRLEN+1]; /* cmd string + \0 */
        } header;
        char    data[0];                /* placeholder for actual data */
};

: $ cat a.c
: #include <sys/types.h>
: #include <netgraph/ng_message.h>
: #include <stdio.h>
: 
: int
: main(void)
: {
: 
:         printf("%d %d\n", sizeof(struct ng_mesg),
:             2 + sizeof(u_int16_t) + sizeof(u_int32_t) * 4 + (NG_CMDSTRLEN + 1));
:         return (0);
: }
: $ make a
: cc -O -pipe   a.c  -o a
: $ ./a
: 36 36


Cheers,
-- 
Ruslan Ermilov
ru at FreeBSD.org
FreeBSD committer
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