Add inotify watch support

Added code to register for inotify events on the needed
path and the user callback on events

Change-Id: I90529f8e96fcbecfe0a1b943c3c435dab79222c3
Signed-off-by: Vishwanatha Subbanna <vishwa@linux.vnet.ibm.com>

1 files changed, 114 insertions, 0 deletions

diff --git a/watch.hpp b/watch.hpp
new file mode 100644
index 0000000..0e20420
--- /dev/null
+++ b/watch.hpp
@@ -0,0 +1,114 @@
+#pragma once
+
+#include "util.hpp"
+#include "types.hpp"
+#include "dns_updater.hpp"
+
+#include <systemd/sd-event.h>
+
+#include <sys/inotify.h>
+#include <map>
+#include <functional>
+#include <experimental/filesystem>
+
+namespace phosphor
+{
+namespace network
+{
+namespace inotify
+{
+
+namespace fs = std::experimental::filesystem;
+
+// Auxiliary callback to be invoked on inotify events
+using UserCallBack = std::function<void(const std::string&)>;
+
+/** @class Watch
+ *
+ *  @brief Adds inotify watch on directory
+ *
+ *  @details Calls back user function on matching events
+ */
+class Watch
+{
+    public:
+        Watch() = delete;
+        Watch(const Watch&) = delete;
+        Watch& operator=(const Watch&) = delete;
+        Watch(Watch&&) = delete;
+        Watch& operator=(Watch&&) = delete;
+
+        /** @brief Hooks inotify watch with sd-event
+         *
+         *  @param[in] eventPtr - Reference to sd_event wrapped in unique_ptr
+         *  @param[in] path     - File path to be watched
+         *  @param[in] userFunc - User specific callback function on events
+         *  @param[in] flags    - Flags to be supplied to inotify
+         *  @param[in] mask     - Mask of events to be supplied to inotify
+         *  @param[in] events   - Events to be watched
+         */
+        Watch(phosphor::network::EventPtr& eventPtr,
+              const fs::path path,
+              UserCallBack userFunc,
+              int flags = IN_NONBLOCK,
+              uint32_t mask = IN_CLOSE_WRITE,
+              uint32_t events = EPOLLIN);
+
+        /** @brief Remove inotify watch and close fd's */
+        ~Watch()
+        {
+            if ((fd() >= 0) && (wd >= 0))
+            {
+                inotify_rm_watch(fd(), wd);
+            }
+        }
+
+    private:
+        /** @brief Callback invoked when inotify event fires
+         *
+         *  @details On a matching event, calls back into user supplied
+         *           function if there is one registered
+         *
+         *  @param[in] eventSource - Event source
+         *  @param[in] fd          - Inotify fd
+         *  @param[in] retEvents   - Events that matched for fd
+         *  @param[in] userData    - Pointer to Watch object
+         *
+         *  @returns 0 on success, -1 on fail
+         */
+        static int processEvents(sd_event_source* eventSource,
+                                 int fd,
+                                 uint32_t retEvents,
+                                 void* userData);
+
+        /** @brief Initializes an inotify instance
+         *
+         *  @return Descriptor on success, -1 on failure
+         */
+        int inotifyInit();
+
+        /** @brief File path to be watched */
+        const fs::path path;
+
+        /** @brief User callback function */
+        UserCallBack userFunc;
+
+        /** @brief Inotify flags */
+        int flags;
+
+        /** @brief Mask of events */
+        uint32_t mask;
+
+        /** @brief Events to be watched */
+        uint32_t events;
+
+        /** @brief Watch descriptor */
+        int wd = -1;
+
+        /** @brief File descriptor manager */
+        phosphor::Descriptor fd;
+};
+
+} // namespace inotify
+} // namespace network
+} // namespace phosphor