Userland: suggestion for the userapi code

[Peter da Silva]

In the userapi example you have:

ssize_t
read(int fd, void *buf, size_t bytes)
{
    SysReadMsg msg;

    initSysReadMsg(&msg, &_sysreplyport, fd, buf, bytes);
    error = _syscallport->mp_SendMsg(syscallport, &msg);
    if (error == EASYNC) {
        error = waitmsg(&msg);
        ... blocks ...
    }
    errno = error;
    return(msg.retcode);
}

I think there would be more flexibility with:

ssize_t
read(int fd, void *buf, size_t bytes)
{
    SysReadMsg msg;
    SysMsgPort *port, *reply; /* or whatever */

    ... check that fd is valid ...
    port = _fdtab[fd].messagePort;
    reply = _fdtab[fd].replyPort;

    initSysReadMsg(&msg, reply, fd, buf, bytes);
    error = port->mp_SendMsg(port, &msg);
    if (error == EASYNC) {
        error = reply->waitmsg(&msg);
        ... blocks ...
    }
    errno = error;
    return(msg.retcode);
}

Most of the time the per-fd ports are the system ports.

This doesn't require any change in the kernel, but it makes user-level
layering a lot easier... you could test and implement pseudo-devices
as an _unprivileged_ user by wrapping open() or you could shortcut
implementations of things like /dev/null or /dev/zero so they made
no kernel crossings at all.

(I hope this doesn't come out in HTML, NewsFlash doesn't seem to have
a way to say "no, I don't bloody want rich text, I don't care how cool
it is"... I need a better newsreader for Mac OS X. I wish TRN had
multiple server support)