Am Fre, 02 Mär 2001 schrieben Sie:
> *Never* called? Or just not called when the FIFO is empty and you
> do a read from it? This is a known problem that I had a quick "fix" for,
never called imo:
int rtfHandler(size_t fifo)
{
size_t sz;
const char *msg = "Hallo World\n";
sz = strlen(msg);
rtf_put(number(), &sz, sizeof(sz));
rtf_put(number(), (void*)msg, sz);
return 0;
}
The first read op from user space should call the handler above. It puts at
first the stringlength and then the string self. On each call the rtf buffer is
filled with the same string. I'm on a wrong way ?
> but was never put in to any releases of RTLinux. I say "fix" because I am not
> sure if it would be compliant with POSIX to act this way (in other words, it
> may be correct by POSIX standards to not call the handler on reads when the
> FIFO is empty). This does seem to severely limit the usefulness of FIFOs,
This make sense, since the buffer is empty. But, I see it like the linux proc
fs - I can call the handler if I want asynchronous to read - only reading info
(which is eq. to my case)! I order infos - nevertheless on empty or not empty
buffers.
The other way would be write a cmd the the kernel task that I wish to have some
infos - the user write handler fills the buffer and than I can read from user
space the info. For that I don't need a handler really since the buffer is
filled and I can read from user space even if no user read handler is installed.
> though. My suggestion is to do sort of an ack an response scheme in your
> handler where the userspace program sends a request via another FIFO, then
> the handler that gets called for that FIFO writes to the FIFO that the user
> space program is reading from. That, or just have a real-time task write
> data to the FIFO whenever it has some to write, until the FIFO is full, and
> have the user space program poll on that FIFO.
Is it really neccessary ? man page says:
rtf_create_handler installs a handler which is executed when data is written
to or read from a real-time fifo (RT-FIFO). fifo is an RT-FIFO that must
have previously been created with a call to rtf_create. handler is
then called whenever a Linux process accesses that fifo.
.....
Thanks
Olaf
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