Misc: --write-pid-path & small changes

- Add --write-pid-path to write process ID to a file, to help
  determining compton's process ID when -b is used.

- Add a few extra targets to query through D-Bus opts_get (version, pid,
  etc.) and through win_get, primarily for debugging.

- Add helper macros likely(), unlikely(), cmalloc(), ccalloc(),
  crealloc().

- Change w->opacity_set to opacity_t. Determine display_repr in
  session_init(), etc.

src/common.h

@@ -60,6 +60,10 @@
 #error Cannot enable c2 debugging without c2 support.
 #endif
 
+#ifndef COMPTON_VERSION
+#define COMPTON_VERSION "unknown"
+#endif
+
 // === Includes ===
 
 // For some special functions
@@ -132,6 +136,12 @@
 #define MSTR_(s)        #s
 #define MSTR(s)         MSTR_(s)
 
+/// @brief Wrapper for gcc branch prediction builtin, for likely branch.
+#define likely(x)    __builtin_expect(!!(x), 1)
+
+/// @brief Wrapper for gcc branch prediction builtin, for unlikely branch.
+#define unlikely(x)  __builtin_expect(!!(x), 0)
+
 /// Print out an error message.
 #define printf_err(format, ...) \
   fprintf(stderr, format "\n", ## __VA_ARGS__)
@@ -431,9 +441,13 @@ typedef struct {
   // === General ===
   /// The configuration file we used.
   char *config_file;
+  /// Path to write PID to.
+  char *write_pid_path;
   /// The display name we used. NULL means we are using the value of the
   /// <code>DISPLAY</code> environment variable.
   char *display;
+  /// Safe representation of display name.
+  char *display_repr;
   /// The backend in use.
   enum backend backend;
   /// Whether to avoid using stencil buffer under GLX backend. Might be
@@ -986,7 +1000,7 @@ typedef struct _win {
   /// _NET_WM_OPACITY value
   opacity_t opacity_prop_client;
   /// Last window opacity value we set.
-  long opacity_set;
+  opacity_t opacity_set;
 
   // Fading-related members
   /// Do not fade if it's false. Change on window type change.
@@ -1150,6 +1164,15 @@ allocchk_(const char *func_name, void *ptr) {
 /// @brief Wrapper of allocchk_().
 #define allocchk(ptr) allocchk_(__func__, ptr)
 
+/// @brief Wrapper of malloc().
+#define cmalloc(nmemb, type) ((type *) allocchk(malloc((nmemb) * sizeof(type))))
+
+/// @brief Wrapper of calloc().
+#define ccalloc(nmemb, type) ((type *) allocchk(calloc((nmemb), sizeof(type))))
+
+/// @brief Wrapper of ealloc().
+#define crealloc(ptr, nmemb, type) ((type *) allocchk(realloc((ptr), (nmemb) * sizeof(type))))
+
 /**
  * Return whether a struct timeval value is empty.
  */
@@ -1310,10 +1333,7 @@ print_timestamp(session_t *ps) {
  */
 static inline char *
 mstrcpy(const char *src) {
-  char *str = malloc(sizeof(char) * (strlen(src) + 1));
-
-  if (!str)
-    printf_errfq(1, "(): Failed to allocate memory.");
+  char *str = cmalloc(strlen(src) + 1, char);
 
   strcpy(str, src);
 
@@ -1325,10 +1345,7 @@ mstrcpy(const char *src) {
  */
 static inline char *
 mstrncpy(const char *src, unsigned len) {
-  char *str = malloc(sizeof(char) * (len + 1));
-
-  if (!str)
-    printf_errfq(1, "(): Failed to allocate memory.");
+  char *str = cmalloc(len + 1, char);
 
   strncpy(str, src, len);
   str[len] = '\0';
@@ -1341,7 +1358,7 @@ mstrncpy(const char *src, unsigned len) {
  */
 static inline char *
 mstrjoin(const char *src1, const char *src2) {
-  char *str = malloc(sizeof(char) * (strlen(src1) + strlen(src2) + 1));
+  char *str = cmalloc(strlen(src1) + strlen(src2) + 1, char);
 
   strcpy(str, src1);
   strcat(str, src2);
@@ -1354,8 +1371,8 @@ mstrjoin(const char *src1, const char *src2) {
  */
 static inline char *
 mstrjoin3(const char *src1, const char *src2, const char *src3) {
-  char *str = malloc(sizeof(char) * (strlen(src1) + strlen(src2)
-        + strlen(src3) + 1));
+  char *str = cmalloc(strlen(src1) + strlen(src2)
+        + strlen(src3) + 1, char);
 
   strcpy(str, src1);
   strcat(str, src2);
@@ -1369,7 +1386,8 @@ mstrjoin3(const char *src1, const char *src2, const char *src3) {
  */
 static inline void
 mstrextend(char **psrc1, const char *src2) {
-  *psrc1 = realloc(*psrc1, (*psrc1 ? strlen(*psrc1): 0) + strlen(src2) + 1);
+  *psrc1 = crealloc(*psrc1, (*psrc1 ? strlen(*psrc1): 0) + strlen(src2) + 1,
+      char);
 
   strcat(*psrc1, src2);
 }