shmlog: store meta information in the buffer itself, store path as X11 atom

This makes i3-dump-log completely independent of a running i3 instance.

include/atoms.xmacro

@@ -26,3 +26,4 @@ xmacro(WM_WINDOW_ROLE)
 xmacro(I3_SOCKET_PATH)
 xmacro(I3_CONFIG_PATH)
 xmacro(I3_SYNC)
+xmacro(I3_SHMLOG_PATH)

include/i3/ipc.h

@@ -40,9 +40,6 @@
 /** Request the configuration for a specific 'bar' */
 #define I3_IPC_MESSAGE_TYPE_GET_BAR_CONFIG      6
 
-/** Request the SHM debug log start/wrap markers */
-#define I3_IPC_MESSAGE_TYPE_GET_LOG_MARKERS     7
-
 /*
  * Messages from i3 to clients
  *
@@ -69,9 +66,6 @@
 /** Bar config reply type */
 #define I3_IPC_REPLY_TYPE_BAR_CONFIG            6
 
-/** Request the SHM debug log start/wrap markers */
-#define I3_IPC_REPLY_TYPE_LOG_MARKERS           7
-
 /*
  * Events from i3 to clients. Events have the first bit set high.
  *

include/libi3.h

@@ -47,13 +47,14 @@ struct Font {
 #endif
 
 /**
- * Try to get the socket path from X11 and return NULL if it doesn’t work.
+ * Try to get the contents of the given atom (for example I3_SOCKET_PATH) from
+ * the X11 root window and return NULL if it doesn’t work.
  *
- * The memory for the socket path is dynamically allocated and has to be
+ * The memory for the contents is dynamically allocated and has to be
  * free()d by the caller.
  *
  */
-char *socket_path_from_x11();
+char *root_atom_contents(const char *atomname);
 
 /**
  * Safe-wrapper around malloc which exits if malloc returns NULL (meaning that

include/log.h

@@ -37,13 +37,6 @@ void init_logging();
  */
 void add_loglevel(const char *level);
 
-/**
- * Returns the offsets for the next write and for the last wrap.
- * Necessary to print the i3 SHM log in the correct order.
- *
- */
-void get_log_markers(int *offset_next_write, int *offset_last_wrap, int *size);
-
 /**
  * Set verbosity of i3. If verbose is set to true, informative messages will
  * be printed to stdout. If verbose is set to false, only errors will be