[zeromq-dev] ZMQ vs SPI: FD shenanigans

[Thomas Rodgers]

No, not really. libc++ doesn't do anything particularly interesting with
fd's but I just wanted to formally rule it out.
Unfortunately I don't have a system (or any experience dealing) with SPI
devices. I don't think libzmq does anything particularly 'funky' with any
of the file descriptors it manages though (at least based on my reading of
the source).

On Tue, Jan 20, 2015 at 8:56 AM, Olaf Mandel <o.mandel at menlosystems.com>
wrote:

> Hello Thomas,
>
> thank you for the quick answer.
>
> Am 20.01.2015 15:11, schrieb Thomas Rodgers:
> > Do you see the same behavior if you replace C with fopen() ?
> -Snipp-
>
> Not quite: if the error occurs, the behaviour is the same as before. But
> now the error _always_ happens: closing the file descriptor in the C
> version of the test makes no difference. New test below:
>
>
> /*
>  *  Compile with:
>  *  g++ -Wall -Werror -Wextra -pedantic -x c -o test test.c -lzmq
>  */
> #include <fcntl.h>
> #include <linux/spi/spidev.h>
> #include <stdio.h>
> #include <string.h>
> #include <sys/ioctl.h>
> #include <zmq.h>
>
>
> /*#define ADDR "tcp://127.0.0.1:8000"*/
> #define ADDR "inproc://addr"
>
>
> /*
>  *  The program always shows the problem (independent of the presence
>  *  of D) for the following permutations of the blocks:
>  *  - A B C D
>  *  - A C B D
>  *  - A C D B
>  *  - C A B D
>  *  - C A D B
>  *  - C D A B
>  *
>  *  With the constraint that A must be before B and C before D, there
>  *  are no further valid permutations.
>  *
>  *  For the TCP address, the error message is: No such device
>  *  For the inproc address, it is: Resource temporarily unavailable
>  */
> int main()
> {
>     void*  ctx;
>     void*  skt;
>     FILE*  f;
>     int    fd;
>     struct spi_ioc_transfer pcks;
>
>     ctx = zmq_ctx_new();            /* A */
>
>     skt = zmq_socket(ctx, ZMQ_PUB); /* B */
>     zmq_bind(skt, ADDR);
>
>     f = fopen("log", "w");          /* C */
>     (void)sizeof(f);
>
>     fclose(f);                      /* D */
>
>     /* The following always last */
>     fd = open("/dev/spidev32766.0", O_RDWR);
>     memset(&pcks, 0, sizeof(struct spi_ioc_transfer));
>     ioctl(fd, SPI_IOC_MESSAGE(1), &pcks);
>     printf("errno: %s\n", strerror(errno));
>
>     return 0;
> }
>
>
> The one advantage of this is: I now at least can see the FILE structure
> and the contained _fileno member.
>
> Any further thoughts?
> Olaf Mandel
> --
> Olaf Mandel
> phone: +49-89-189166-250
> fax:   +49-89-189166-111
> Menlo Systems GmbH
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>
>
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