I am struggling to read back the value of a pin that I set before.
Is this even possible? (It is using sysfs!)

I have this code:

#include <gpiod.h> // gpiod_line_set_value, gpiod_line_get_value
#include <stdio.h>

// Open gpio device and read/write gpio pin

const char CHIP[] = "/dev/gpiochip1";
const int LINE = 3; // EN_FAN

// if arg 1 is 0/1, write to gpio pin else read from gpio pin

int main(int argc, char* argv[])
{
   struct gpiod_chip* chip;
   struct gpiod_line* line;
   int val;

   chip = gpiod_chip_open(CHIP);
   if (!chip)
   {
      perror("Open chip failed");
      return 1;
   }

   line = gpiod_chip_get_line(chip, LINE);
   if (!line)
   {
      perror("Get line failed");
      gpiod_chip_close(chip);
      return 1;
   }

   if (argc == 2) // write
   {
      val = atoi(argv[1]);
      if (gpiod_line_request_output(line, "gpiot", val))
      {
         perror("Request line as output failed");
         gpiod_line_release(line);
         gpiod_chip_close(chip);
         return 1;
      }
      // No need to set. Default value in request_output is applied.
      val = gpiod_line_get_value(line);
      if (val == 0 || val == 1)
      {
         printf("Line value: %dn", val);
      }
      else
      {
         perror("Get line value failed");
         gpiod_line_release(line);
         gpiod_chip_close(chip);
         return 1;
      }
   }
   else // read
   {
      if (gpiod_line_request_input(line, "gpiot"))
      {
         perror("Request line as input failed");
         gpiod_line_release(line);
         gpiod_chip_close(chip);
         return 1;
      }
      val = gpiod_line_get_value(line);
      if (val < 0)
      {
         perror("Get line value failed");
         gpiod_line_release(line);
         gpiod_chip_close(chip);
         return 1;
      }
      printf("Line value: %dn", val);
   }

   gpiod_line_release(line);
   gpiod_chip_close(chip);

   return 0;
}

I have a gpiod_line_get_value() right after gpiod_line_request_output(). It always reads 0 regardless of what the pin is set to. (Setting the pin works, I can see the fan running).

Opening the pin in input mode (no argument to executable, gpiod_line_request_input) resets the pin. The fan no longer runs.

Additional question: Using gpiod_line_request_output instead of gpiod_line_request_output_flags used default flags (no bit set). This means it keeps the flags from before, right? The settings that were set from the kernel/device tree.