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. 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.
