OH MY GOD! Excellent catch!! I sincerely hope the fsmlabs team accepts
your fix for inclusion into future versions of rtf.
What is a user pair? Is it combining 2 fifo's from the kernel into 1 user
fifo? What is the point of this?
On Fri, 16 Nov 2001, John_Jacques wrote:
> I just fixed a similiar problem in rtl_fifo.c that caused linux
> applications to stay blocked after an RTLinux module called rtf_put.
> Note the following from the end of rtf_put in rtl_fifo.c
>
> if (RTF_USER_OPEN(minor)) {
> fifo_wake_sleepers(minor);
> }
>
> If you make a user pair only one minor number is open
> (RTF_USER_OPEN(minor) != 0). Consider the following sequence of events:
>
> /* In init_module( ) */
> rtf_create( 10, size );
> rtf_create( 11, size );
> rtf_make_user_pair( 10, 11 );
>
> /* Linux application */
> file_descriptor = open( "/dev/rtf10", O_RDWR );
> read( file_descriptor, buffer, size );
>
> At this point RTF_USER_OPEN( 10 ) equals 2, RTF_USER_OPEN( 11 ) equals 0
> and the Linux application is blocked on the read.
>
> /* RTLinux module */
> rtf_put( 11, buffer, size );
>
> The code, noted above, in rtl_fifo.c does not wake up the linux
> application!
> My fix is as follows:
>
> if( RTF_USER_OPEN( minor ) ||
> ( ( 0 != RTF_BI( minor ) ) &&
> RTF_USER_OPEN( minor + RTF_BI( minor ) ) ) ) {
> fifo_wake_sleepers(minor - (RTF_BI(minor) < 0));
> }
>
> "Calin A. Culianu" wrote:
> >
> > What is supposed to happen when a user-process does the following?
> >
> > int n_ready;
> > fd_set rfds;
> >
> > /* assume fd is an already-opened /dev/rtf */
> > ioctl(fd, FIONREAD, &n_ready);
> >
> > if (n_ready == 0) {
> >
> > FD_ZERO(&rfds);
> > FD_SET(fd, &rfds);
> > select (fd+1, &rfds, NULL, NULL, NULL); /* block indefinitely waiting
> > for new stuff on fd */
> >
> > }
> >
> > Basically the above code snippet blocks forever whenever the ioctl
> > detects 0 bytes ready for reading.. even though I *know* my real-time thread
> > is generating more data on the fifo...
> >
> > Is this a bug/lacking feature of /dev/rtf or a simple stupid thing i am
> > overlooking? I guess I can open up the rtl_fifo.c file and have a gander
> > at it myself.... but maybe one of you can save me the trouble.. thanks!
> >
> > And I know.. I could just open the fifo with blocking reads, but I
> > wanted to see if I could selectively block and not block on demand using
> > select()...
> >
> > -Calin
> >
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