[openbeos] Re: SK: interacting modules
- From: François Revol <revol@xxxxxxx>
- To: openbeos@xxxxxxxxxxxxx
- Date: Tue, 14 May 2002 18:39:35 +0200 (MEST)
right, the kernel only knows about ports.
basically, when an application wants to send a BMessage, it searches for
the port the BHandler watches, Flatten()s the message, and use the
write_port() syscall to send it, on the other side, the waiting thread
is blocked on read_port() which fills in a buffer with the flattened BMessage,
and it Unflattens it from the buffer.
// sender code
// something like this :)
BMessenger::SendMessage(BMessage *a_message)
{
char *buffer;
size_t size;
buffer = new char[size = a_message->FlattenedSize()];
a_message->Flatten(buffer, size);
write_port(fPort, a_message->What(), buffer, size);
delete buffer;
}
As for kernel notification, I suspect the use of semaphores...
not sure though.
En réponse à Axel Dörfler <axeld@xxxxxxxxxxxxxxxx>:
> > * Node Monitoring:
> > Basically the two functions watch_node() and stop_watching(), but
> > who
> > does the actual work? Is there a Node Monitor (the BeBook mentions
> > something like this)? ...?
>
> That's handled by the notify_listener() function - the file system
> calls that function (a kernel function), and it will somehow trigger
> the notification of all watching messengers.
> AFAIK the kernel has no knowledge about BMessages, so it must be
> handled by some upper layer - I guess it's either the app_server or the
>
> registrar, but I dunno.
>
> > * BQuery:
> > Static queries can be mapped to the fs_*_query() functions in
> > libroot
> > and thus are certainly related more closely to the kernel.
> > But how is the additional functionality for live queries provided?
>
> > Who
> > does this? Are live queries somehow related to node monitoring?
>
> That's similar to the above - a file system uses the
> send_notification() function (note, that its parameters aren't
> documented anywhere, and we will have to find out in BFS how it is
> supposed to work), and the kernel will most probably trigger some upper
>
> layer to send out the notification messages.
> Looking at the disassembled kernel sources (no, no I wouldn't do that
> :), notify_listener() calls send_notification() itself (also
> sys_mount() does this), so it appears that send_notification() is the
> "work horse" of that thing. At the end of the function, it does a
> write_port_etc(), but I haven't had a look which port it is using for
> this. For queries, there is a fs_open_live_query() function which also
>
> takes a port ID as argument - unfortunately, I couldn't find a server
> or library which would call this function, which means that there is
> some other function used for this.
>
> Adios...
> Axel.
>
>
>
>
Other related posts:
