Programming

I have to make a linux monitoring daemon that works with a SPI device (/dev/spidev). However, I always failed to init this SPI device. The return error code is 25, which means "inappropriate ioctl for device". As I know, daemon runs in background and doesn't have a control terminal and this might be the reason that caused SPI device failed to init.

If I make a similar program and run it manually under Linux shell then it can init the SPI device properly without any problem.

My question is: Is there a way to init the SPI device if I run my program as a daemon?

Thank you

"inappropriate ioctl for device" is odd. Without seeing your actual code, we're only guessing what's going wrong, but if I had to guess -- it may not actually succeed in opening the device, doesn't check whether it did, and ends up doing ioctl() on FD 0 or somesuch. Which for a daemon probably ends up being /dev/null.

Hi Corona,

Thanks for your suggestion. Here is the log from strace:

_newselect(0, NULL, NULL, NULL, {0, 16576}) = 0 (Timeout)
open("/dev/spidev0.0", O_RDWR) = 6
ioctl(6, 0x80406b00, 0x7f812fe0) = 4
time([987124305]) = 987124305
getpid() = 881
socket(PF_FILE, SOCK_DGRAM, 0) = 7
fcntl64(7, F_SETFD, FD_CLOEXEC) = 0
connect(7, {sa_family=AF_FILE, path="/dev/log"}, 16) = -1 ENOENT (No such file or directory)
close(7) = 0
time([987124305]) = 987124305
getpid() = 881
socket(PF_FILE, SOCK_DGRAM, 0) = 7
fcntl64(7, F_SETFD, FD_CLOEXEC) = 0
connect(7, {sa_family=AF_FILE, path="/dev/log"}, 16) = -1 ENOENT (No such file or directory)
close(7)


If I enable syslog, then here is the log from syslog:
Apr 13 01:20:23 UNKNOWN[881]: -----------------------------------
Apr 13 01:20:23 UNKNOWN[881]: SPIRead:467 Error No. [25], Error: [Inappropriate ioctl for device]
Apr 13 01:20:23 UNKNOWN[881]: -----------------------------------
Apr 13 01:20:23 UNKNOWN[881]: _IOC_NR(SPI_IOC_MESSAGE( 0)) 0
Apr 13 01:20:23 UNKNOWN[881]: _IOC_NR(SPI_IOC_MESSAGE(1)) 0
Apr 13 01:20:23 UNKNOWN[881]: _IOC_NR(SPI_IOC_MESSAGE(2)) 0
Apr 13 01:20:23 UNKNOWN[881]: _IOC_DIR(SPI_IOC_MESSAGE(2)) 4
Apr 13 01:20:23 UNKNOWN[881]: _IOC_WRITE 4

Do you have any comment on this?

From man ioctl:

Code:

RETURN VALUE
       Usually, on success zero is returned.  A few ioctl() requests  use  the
       return  value  as an output parameter and return a nonnegative value on
       success.  On error, -1 is returned, and errno is set appropriately.

Again, without seeing your code, I'm only guessing, but your code may be incorrectly assuming all nonzero return values mean error, not just negative returns.