add function write_file() (#2181)

* add function write_file()

* handle EAGIN & EWOULDBLOCK

* don't  handle errno

selfdrive/common/framebuffer.cc

@@ -1,3 +1,4 @@
+#include "util.h"
 #include <cstdio>
 #include <cstdlib>
 #include <cassert>
@@ -37,13 +38,9 @@ extern "C" void framebuffer_swap(FramebufferState *s) {
 }
 
 extern "C" bool set_brightness(int brightness) {
-  FILE *f = fopen("/sys/class/leds/lcd-backlight/brightness", "wb");
-  if (f != NULL) {
-    fprintf(f, "%d", brightness);
-    fclose(f);
-    return true;
-  }
-  return false;
+  char bright[64];
+  snprintf(bright, sizeof(bright), "%d", brightness);
+  return 0 == write_file("/sys/class/leds/lcd-backlight/brightness", bright, strlen(bright));
 }
 
 extern "C" void framebuffer_set_power(FramebufferState *s, int mode) {

selfdrive/common/gpio.cc

@@ -1,75 +1,29 @@
 #include "gpio.h"
+#include "util.h"
 #include <fcntl.h>
 #include <unistd.h>
-#include <stdio.h>
+#include <string.h>
 
 // We assume that all pins have already been exported on boot,
 // and that we have permission to write to them.
 
 int gpio_init(int pin_nr, bool output){
-  int ret = 0;
-  int fd = -1, tmp;
-
   char pin_dir_path[50];
   int pin_dir_path_len = snprintf(pin_dir_path, sizeof(pin_dir_path),
                            "/sys/class/gpio/gpio%d/direction", pin_nr);
   if(pin_dir_path_len <= 0){
-    ret = -1;
-    goto cleanup;
+    return -1;
   }
-
-  fd = open(pin_dir_path, O_WRONLY);
-  if(fd == -1){
-    ret = -1;
-    goto cleanup;
-  }
-  if(output){
-    tmp = write(fd, "out", 3);
-    if(tmp != 3){
-      ret = -1;
-      goto cleanup;
-    }
-  } else {
-    tmp = write(fd, "in", 2);
-    if(tmp != 2){
-      ret = -1;
-      goto cleanup;
-    }
-  }
-
-cleanup:
-  if(fd >= 0){
-    close(fd);
-  }
-  return ret;
+  const char *value = output ? "out" : "in";
+  return write_file(pin_dir_path, (void*)value, strlen(value));
 }
 
 int gpio_set(int pin_nr, bool high){
-  int ret = 0;
-  int fd = -1, tmp;
-
   char pin_val_path[50];
   int pin_val_path_len = snprintf(pin_val_path, sizeof(pin_val_path),
                            "/sys/class/gpio/gpio%d/value", pin_nr);
   if(pin_val_path_len <= 0){
-    ret = -1;
-    goto cleanup;
+    return -1;
   }
-
-  fd = open(pin_val_path, O_WRONLY);
-  if(fd == -1){
-    ret = -1;
-    goto cleanup;
-  }
-  tmp = write(fd, high ? "1" : "0", 1);
-  if(tmp != 1){
-    ret = -1;
-    goto cleanup;
-  }
-
-cleanup:
-  if(fd >= 0){
-    close(fd);
-  }
-  return ret;
+  return write_file(pin_val_path, (void*)(high ? "1" : "0"), 1);
 }

selfdrive/common/util.c

@@ -3,7 +3,8 @@
 #include <string.h>
 #include <assert.h>
 #include <unistd.h>
-
+#include <fcntl.h>
+#include <errno.h> 
 #ifdef __linux__
 #include <sys/prctl.h>
 #include <sys/syscall.h>
@@ -41,6 +42,16 @@ void* read_file(const char* path, size_t* out_len) {
   return buf;
 }
 
+int write_file(const char* path, const void* data, size_t size) {
+  int fd = open(path, O_WRONLY);
+  if (fd == -1) {
+    return -1;
+  }
+  ssize_t n = write(fd, data, size);
+  close(fd);
+  return n == size ? 0 : -1;
+}
+
 void set_thread_name(const char* name) {
 #ifdef __linux__
   // pthread_setname_np is dumb (fails instead of truncates)

selfdrive/common/util.h

@@ -41,6 +41,7 @@ extern "C" {
 // Returns NULL on failure, otherwise the NULL-terminated file contents.
 // The result must be freed by the caller.
 void* read_file(const char* path, size_t* out_len);
+int write_file(const char* path, const void* data, size_t size);
 
 void set_thread_name(const char* name);