feedbackd: Add helper to set up permissions for LEDs

This helper knows about the tiggers and necessary permission.
It's intended to be run via udev.

src/fbd-ledctrl.c

+/*
+ * Copyright (C) 2020 Purism SPC
+ * SPDX-License-Identifier: GPL-3.0+
+ * Author: Guido Günther <agx@sigxcpu.org>
+ */
+
+#define G_LOG_DOMAIN "fbd-ledctrl"
+
+#include <glib.h>
+
+#include <errno.h>
+#include <fcntl.h>
+#include <grp.h>
+#include <stdio.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+#define LED_BRIGHTNESS_ATTR "brightness"
+#define LED_PATTERN_ATTR    "pattern"
+#define LED_REPEAT_ATTR     "repeat"
+#define LED_TRIGGER_ATTR    "trigger"
+#define LED_TRIGGER_PATTERN "pattern"
+
+enum {
+  FBD_LEDCTRL_ERR_CMDLINE = 1,
+  FBD_LEDCTRL_ERR_TRIGGER = 2,
+  FBD_LEDCTRL_ERR_PERMS   = 3,
+};
+
+static gboolean
+write_sysfs_attr (const char *sysfs_path, const char *attr, const char *val)
+{
+  gint fd;
+  int len;
+  g_autofree gchar *path = g_strjoin ("/", sysfs_path, attr, NULL);
+
+  fd = open (path, O_WRONLY|O_TRUNC, 0666);
+  if (fd < 0) {
+    fprintf (stderr, "Failed to open %s: %s\n", path, strerror (errno));
+    return FALSE;
+  }
+
+  len = strlen (val);
+  if (write (fd, val, len) < 0) {
+    fprintf (stderr, "Failed to write %s to %s: %s\n", val, path, strerror (errno));
+    close (fd);
+    return FALSE;
+  }
+
+  if (close (fd) < 0) {
+    fprintf (stderr, "Failed to close %s: %s\n", path, strerror (errno));
+    return FALSE;
+  }
+
+  return TRUE;
+}
+
+static gchar *
+read_sysfs_attr (const char *sysfs_path, const char *attr)
+{
+  gchar *content = NULL;
+  g_autoptr (GError) err = NULL;
+  g_autofree gchar *path = g_strjoin ("/", sysfs_path, attr, NULL);
+
+
+  if (!g_file_get_contents (path, &content, NULL, &err)) {
+    fprintf (stderr, "Failed to read %s: %s\n", path, err->message);
+    return NULL;
+  }
+  
+  return content;
+}
+
+static gboolean
+set_sysfs_attr_perm (const char *sysfs_path, const char *attr, gid_t gid)
+{
+  g_autofree gchar *path = g_strjoin ("/", sysfs_path, attr, NULL);
+  
+  if (chown(path, -1, gid) < 0) {
+    fprintf (stderr, "Failed to set perms of %s to %d: %s\n", path, gid, strerror (errno));
+    return FALSE;
+  }
+
+  if (chmod(path, 0664) < 0) {
+    fprintf (stderr, "Failed to set mode of %s: %s\n", path, strerror (errno));
+    return FALSE;
+  }
+  
+  return TRUE;
+}
+
+static gboolean
+set_trigger (const char *sysfs_path, const char *trigger)
+{
+  g_autofree gchar *val = NULL;
+  g_auto(GStrv) triggers = NULL;
+
+  /*
+   * Check the current trigger, don't do anything if it's already
+   * set. This prevents a change event storm when setting the
+   * same trigger over and over again in a udev rule.
+   */
+  val = read_sysfs_attr (sysfs_path, LED_TRIGGER_ATTR);
+  triggers = g_strsplit (val, " ", 0);
+
+  /* 
+   * The active trigger is marked with [...] so if we don't find the
+   * trigger verbatim it's already the active one:
+   */
+  if (!g_strv_contains ((const gchar * const *)triggers, trigger))
+    return TRUE;
+
+  return write_sysfs_attr (sysfs_path, LED_TRIGGER_ATTR, trigger);
+}
+
+static gboolean
+set_perms (const char *sysfs_path, const char *trigger, const char *gname)
+{
+  struct group *group;
+  gboolean success = TRUE;
+
+  group = getgrnam (gname);
+
+  if (!set_sysfs_attr_perm (sysfs_path, LED_BRIGHTNESS_ATTR, group->gr_gid))
+      return FALSE;
+
+  if (!g_strcmp0 (trigger, LED_TRIGGER_PATTERN)) {
+    if (!set_sysfs_attr_perm (sysfs_path, LED_PATTERN_ATTR, group->gr_gid))
+      success = FALSE;
+    if (!set_sysfs_attr_perm (sysfs_path, LED_REPEAT_ATTR, group->gr_gid))
+      success = FALSE;
+  }
+
+  /* specific setup for other triggers goes here */
+  return success;
+}
+
+int main(int argc, char *argv[])
+{
+  g_autoptr(GError) err = NULL;
+  g_autoptr(GOptionContext) opt_context = NULL;
+  g_autofree gchar *sysfs_path = NULL;
+  g_autofree gchar *group = NULL;
+  g_autofree gchar *trigger = NULL;
+
+  const GOptionEntry options [] = {
+    {"path", 'p', 0, G_OPTION_ARG_STRING, &sysfs_path,
+     "Path to LEDs sysfs dir", NULL},
+    {"group", 'G', 0, G_OPTION_ARG_STRING, &group,
+     "Group to set permissions to", NULL},
+    {"trigger", 't', 0, G_OPTION_ARG_STRING, &trigger,
+     "LED trigger to configure", NULL},
+    { NULL, 0, 0, G_OPTION_ARG_NONE, NULL, NULL, NULL }
+  };
+
+  opt_context = g_option_context_new ("- helper to prepare sysfs for feedbackd");
+  g_option_context_add_main_entries (opt_context, options, NULL);
+  if (!g_option_context_parse (opt_context, &argc, &argv, &err)) {
+    fprintf (stderr, "%s", err->message);
+    g_clear_error (&err);
+    return 1;
+  }
+
+  if (!sysfs_path) {
+    fprintf (stderr, "No sysfs path given\n");
+    return FBD_LEDCTRL_ERR_CMDLINE;
+  }
+
+  if (!trigger) {
+    fprintf (stderr, "No trigger specified\n");
+    return FBD_LEDCTRL_ERR_CMDLINE;;
+  }
+  g_debug ("Configuring LED at %s for trigger %s", sysfs_path, trigger);
+
+  if (!set_trigger (sysfs_path, trigger))
+    return FBD_LEDCTRL_ERR_TRIGGER;
+
+  if (group) {
+    g_debug ("Setting permision of %s to %s", sysfs_path, group);
+    if (!set_perms (sysfs_path, trigger, group))
+      return FBD_LEDCTRL_ERR_PERMS;
+  }
+    
+  return 0;
+}

src/meson.build

@@ -65,4 +65,13 @@ executable(
   install_dir: libexecdir,
 )
 
+executable(
+  'fbd-ledctrl',
+  sources : ['fbd-ledctrl.c'],
+  include_directories : fbd_inc,
+  dependencies : [glib],
+  install : true,
+  install_dir: libexecdir,
+)
+
 endif