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Date: Tue, 29 Apr 2008 06:57:25 +1000
From: "Graham Dumpleton" <graham.dumpleton@gmail.com>
To: modules-dev@httpd.apache.org
Subject: Re: need some help with module that does not work on linux
In-Reply-To: <4816253B.8090403@sequoiagroup.com>
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References: <c7f54a760804281009m1bc0a84dt289056ad0f856b3f@mail.gmail.com>
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	 <4816253B.8090403@sequoiagroup.com>

2008/4/29 Chris Kukuchka <chrisk@sequoiagroup.com>:
> Aivars =8Aterns wrote:
>
> > Yes, but this is not how apache could handle this, we need argv[], but
> there
> > is no way to get this from apache right?
> >
> >
>
>  In server/main.c, argv gets linked to the process_rec structure during t=
he
> process startup.  Further, according to include/httpd.h, the process_rec
> structure can be reached through the request_rec structure
> (r->connection->server->process).  As such, argv[] should be available fo=
r
> reading most anywhere in Apache.
>
>  As far as the safety of making changes to those values is concerned, I h=
ave
> no advise beyond, "proceed with caution."  Especially if you intend on
> placing raw request data there.

Although you can get access to argv[], you can only change the value
of argv[0], at least for the purposes of effecting the output from
'ps'. This is because that argv[] is not the original argv[] and thus
modules could have substituted the program arguments, ie., argv[1] and
beyond. This means that any value you substitute must fit into the
original length of argv[0] and cannot flow over into the additional
arguments.

Some code form mod_wsgi:

static void wsgi_setup_daemon_name(WSGIDaemonProcess *daemon, apr_pool_t *p=
)
{
    const char *display_name =3D NULL;

    int slen =3D 0;
    int dlen =3D 0;

    char *argv0 =3D NULL;

    display_name =3D daemon->group->display_name;

    if (!display_name)
        return;

    if (!strcmp(display_name, "%{GROUP}")) {
        display_name =3D apr_pstrcat(p, "(wsgi:", daemon->group->name,
                                   ")", NULL);
    }

    /*
     * Only argv[0] is guaranteed to be the real things as MPM
     * modules may make modifications to subsequent arguments.
     * Thus can only replace the argv[0] value. Because length
     * is restricted, need to truncate display name if too long.
     */

    argv0 =3D (char*)wsgi_server->process->argv[0];

    dlen =3D strlen(argv0);
    slen =3D strlen(display_name);

    memset(argv0, ' ', dlen);

    if (slen < dlen)
        memcpy(argv0, display_name, slen);
    else
        memcpy(argv0, display_name, dlen);
}

The wsgi_server variable is a cached reference to server_rec structure.

Graham