[zeromq-dev] ZMQ vs SPI: FD shenanigans

Olaf Mandel o.mandel at menlosystems.com
Tue Jan 20 15:56:14 CET 2015

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() ?

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://"*/
#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 */

    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
Am Klopferspitz 19a, D-82152 Martinsried
Amtsgericht München HRB 138145
Geschäftsführung: Dr Michael Mei, Dr Ronald Holzwarth
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