Any forward traction ? On Thu, Jul 2, 2015 at 8:51 AM, William Hermans <[email protected]> wrote:
> DO also keep in mind that /sys/ is a pseudo file system. SO does not > always play by the same rules as disk based file systems. > > On Thu, Jul 2, 2015 at 8:50 AM, William Hermans <[email protected]> wrote: > >> >> root@beaglebone:/home/debian# *echo 0 > /sys/class/gpio/export* >> root@beaglebone:/home/debian# l*s /sys/class/gpio/* >> export gpio0 gpiochip0 gpiochip32 gpiochip64 gpiochip96 unexport >> root@beaglebone:/home/debian# *echo 0 > /sys/class/gpio/unexport* >> root@beaglebone:/home/debian# *ls /sys/class/gpio/* >> export gpiochip0 gpiochip32 gpiochip64 gpiochip96 unexport >> >> >> So . . .write only.Here is a decent read on the subject. >> http://falsinsoft.blogspot.com/2012/11/access-gpio-from-linux-user-space.html >> >> On Thu, Jul 2, 2015 at 4:50 AM, Brendan Merna <[email protected]> >> wrote: >> >>> Thanks! That makes a lot of sense now. I figured out I have to open >>> export as write only which agrees with the permissions you showed. I've >>> moved GPIOs to export while the board was running using the command line, >>> so I think its okay. >>> >>> So changing my code subsituting O_WRONLY for O_RDWR and now I'm getting >>> the error "Writing Error: Device or Resource is busy." It doesn't seem like >>> I can use C code to bring a GPIO to the user space. Is there a way around >>> it? >>> >>> I'll look up the process forking too. >>> >>> On Wednesday, July 1, 2015 at 5:22:01 PM UTC-4, William Hermans wrote: >>>> >>>> Also, as I'm unsure what exporting a pin config will do while the >>>> system is running . . . you should make 100% absolutely sure you know what >>>> you're doing. So you do not fry your board. >>>> >>>> On Wed, Jul 1, 2015 at 2:19 PM, William Hermans <[email protected]> >>>> wrote: >>>> >>>>> debian@beaglebone:~$ *cat /sys/class/gpio/export* >>>>> cat: /sys/class/gpio/export: *Permission denied* >>>>> debian@beaglebone:~$ sudo *cat /sys/class/gpio/export* >>>>> cat: /sys/class/gpio/export: *Permission denied* >>>>> debian@beaglebone:~$ *sudo su* >>>>> root@beaglebone:/home/debian# *cat /sys/class/gpio/export* >>>>> cat: /sys/class/gpio/export: *Permission denied* >>>>> root@beaglebone:/home/debian# *ls -al /sys/class/gpio/* >>>>> total 0 >>>>> drwxr-xr-x 2 root root 0 Dec 31 1999 . >>>>> drwxr-xr-x 59 root root 0 Dec 31 1999 .. >>>>> *--w------- *1 root root 4096 Dec 31 1999 export >>>>> lrwxrwxrwx 1 root root 0 Dec 31 1999 gpiochip0 -> >>>>> ../../devices/virtual/gpio/gpiochip0 >>>>> lrwxrwxrwx 1 root root 0 Dec 31 1999 gpiochip32 -> >>>>> ../../devices/virtual/gpio/gpiochip32 >>>>> lrwxrwxrwx 1 root root 0 Dec 31 1999 gpiochip64 -> >>>>> ../../devices/virtual/gpio/gpiochip64 >>>>> lrwxrwxrwx 1 root root 0 Dec 31 1999 gpiochip96 -> >>>>> ../../devices/virtual/gpio/gpiochip96 >>>>> --w------- 1 root root 4096 Dec 31 1999 unexport >>>>> root@beaglebone:/home/debian# *whoami* >>>>> root >>>>> >>>>> read this post . . >>>>> >>>>> >>>>> http://unix.stackexchange.com/questions/118716/unable-to-write-to-a-gpio-pin-despite-file-permissions-on-sys-class-gpio-gpio18 >>>>> >>>>> 3rd post or second answer should fix you up. However do note that what >>>>> you're trying to do is "wrong". Meaning: it is insecure. You ( and I too ) >>>>> need to read up on process forking. IN short, and perhaps somewhat >>>>> incorrect( as I'm not 100% up to speed either ) is that you fork a >>>>> process, >>>>> running privileged commands, and when that command is done, the privileges >>>>> are done too . . . >>>>> >>>>> Anyway, probably safer to add your regular user to a group that has >>>>> limited access to that file. >>>>> >>>>> >>>>> On Wed, Jul 1, 2015 at 8:02 AM, Brendan Merna <[email protected]> >>>>> wrote: >>>>> >>>>>> >>>>>> I'm trying to manipulate my GPIOs using C code and running into >>>>>> "Permission Denied" when running my code and opening the file >>>>>> /sys/class/gpio/export. I'm using nano editor, compiling on the >>>>>> Beaglebone >>>>>> with gcc, and I'm under root user. >>>>>> >>>>>> I would like to do this, so I can set directions and values for the >>>>>> GPIOs with my code. I've heard this might be a problem with user and >>>>>> kernel >>>>>> space conflicting. I know there are library calls in python and other >>>>>> languages to do this that work. Does anyone know what this problem might >>>>>> be >>>>>> and our their alternate calls I can do in C? >>>>>> >>>>>> I tried to just include the necessary parts of the code. >>>>>> Code: >>>>>> #include<fcntl.h> >>>>>> static const char *GPIO_PATH = "/sys/class/gpio/export"; >>>>>> int main(){ >>>>>> int file; >>>>>> if ((file = open(GPIO_PATH, O_RDWR))<0){ >>>>>> perror("GPIO: Can't open the device."); >>>>>> return -1; >>>>>> } >>>>>> return 0; >>>>>> } >>>>>> >>>>>> -- >>>>>> For more options, visit http://beagleboard.org/discuss >>>>>> --- >>>>>> You received this message because you are subscribed to the Google >>>>>> Groups "BeagleBoard" group. >>>>>> To unsubscribe from this group and stop receiving emails from it, >>>>>> send an email to [email protected]. >>>>>> For more options, visit https://groups.google.com/d/optout. >>>>>> >>>>> >>>>> >>>> -- >>> For more options, visit http://beagleboard.org/discuss >>> --- >>> You received this message because you are subscribed to the Google >>> Groups "BeagleBoard" group. >>> To unsubscribe from this group and stop receiving emails from it, send >>> an email to [email protected]. >>> For more options, visit https://groups.google.com/d/optout. >>> >> >> > -- For more options, visit http://beagleboard.org/discuss --- You received this message because you are subscribed to the Google Groups "BeagleBoard" group. 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