Deamon management

daemon/config_watch.cpp

@@ -0,0 +1,109 @@
+// gKeyMapper daemon - watches the mappings file for changes (inotify).
+
+#include "config_watch.h"
+
+#include <cerrno>
+#include <cstdint>
+#include <cstdio>
+#include <cstring>
+
+#include <sys/inotify.h>
+#include <sys/stat.h>
+#include <unistd.h>
+
+namespace gkeymapper::daemon {
+
+namespace {
+
+// IN_CLOSE_WRITE is the useful one (the writer closed the file); IN_MODIFY
+// covers writers that hold the file open, IN_MOVED_TO/CREATE the atomic save.
+constexpr uint32_t kMask = IN_CLOSE_WRITE | IN_MODIFY | IN_MOVED_TO | IN_CREATE;
+
+std::string directory_of(const std::string& path) {
+    size_t slash = path.find_last_of('/');
+    if (slash == std::string::npos) {
+        return ".";
+    }
+    return slash == 0 ? std::string("/") : path.substr(0, slash);
+}
+
+std::string basename_of(const std::string& path) {
+    size_t slash = path.find_last_of('/');
+    return slash == std::string::npos ? path : path.substr(slash + 1);
+}
+
+} // namespace
+
+ConfigWatcher::~ConfigWatcher() {
+    if (fd_ >= 0) {
+        ::close(fd_);
+    }
+}
+
+bool ConfigWatcher::init(const std::string& path) {
+    name_ = basename_of(path);
+    directory_ = directory_of(path);
+
+    fd_ = inotify_init1(IN_NONBLOCK | IN_CLOEXEC);
+    if (fd_ < 0) {
+        std::fprintf(stderr,
+                     "gkeymapper-daemon: inotify unavailable (%s); "
+                     "use SIGHUP to reload\n",
+                     std::strerror(errno));
+        return false;
+    }
+
+    int watch = inotify_add_watch(fd_, directory_.c_str(), kMask);
+    if (watch < 0 && errno == ENOENT) {
+        // First start before anything was ever saved: create the directory the
+        // GUI would create and try once more.
+        ::mkdir(directory_.c_str(), 0755);
+        watch = inotify_add_watch(fd_, directory_.c_str(), kMask);
+    }
+    if (watch < 0) {
+        std::fprintf(stderr,
+                     "gkeymapper-daemon: cannot watch %s (%s); "
+                     "use SIGHUP to reload\n",
+                     directory_.c_str(), std::strerror(errno));
+        ::close(fd_);
+        fd_ = -1;
+        return false;
+    }
+
+    std::fprintf(stderr, "gkeymapper-daemon: watching %s for changes\n",
+                 directory_.c_str());
+    return true;
+}
+
+void ConfigWatcher::poll_events() {
+    if (fd_ < 0) {
+        return;
+    }
+
+    alignas(inotify_event) char buffer[4096];
+    for (;;) {
+        ssize_t length = ::read(fd_, buffer, sizeof(buffer));
+        if (length <= 0) {
+            return; // nothing queued (EAGAIN) or a read error
+        }
+        for (ssize_t offset = 0; offset < length;) {
+            const auto* event = reinterpret_cast<const inotify_event*>(buffer + offset);
+            offset += static_cast<ssize_t>(sizeof(inotify_event)) + event->len;
+
+            // Only the configured file matters; the directory may hold others.
+            if (event->len == 0 || name_ == event->name) {
+                pending_ = true;
+            }
+        }
+    }
+}
+
+bool ConfigWatcher::take_change() {
+    if (!pending_) {
+        return false;
+    }
+    pending_ = false;
+    return true;
+}
+
+} // namespace gkeymapper::daemon