DragonFly kernel List (threaded) for 2003-07
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Re: Userland: suggestion for the userapi code
: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)
Ah, the first rule of writing examples into web pages: They become
instantly obsolete.
In fact the proper 'reply' port is likely going to be built into the
thread structure, e.g. &curthread->td_replyPort or something like
that (the usermode equivalent, that is). We probably do not want
to associate the reply port with the descriptor, because the reply
port really has nothing to do with the descriptor and everything to do
with whoever is sending the message.
I agree with in regards to storing the target port as part of the
FD array. Some care must be taken with anything descriptor based
because the dynamic ELF loader itself (ld.so) will have to be able
to work with it, but the target port will wind up being the 'real'
descriptor here I wager.
-Matt
Matthew Dillon
<dillon@xxxxxxxxxxxxx>
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