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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