Re: Packing netgraph structs

From: Ruslan Ermilov (ru_at_FreeBSD.org)
Date: 07/01/04

  • Next message: Roman Kurakin: "Re: Packing netgraph structs" 
    Date: Thu, 1 Jul 2004 17:10:56 +0300
To: Anil Madhavapeddy <anil@recoil.org>

    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@FreeBSD.org
FreeBSD committer

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