Implement advisory locking for WIM overwrites
[wimlib] / src / write.c
index b143f16d7dc4de001a0e3e2b2cd01b248ffcd593..773de0b7b6553e61ead5ef8b726e00f218b54f6a 100644 (file)
 #include <stdlib.h>
 #endif
 
+#if defined(HAVE_SYS_FILE_H) && defined(HAVE_FLOCK)
+#include <sys/file.h>
+#endif
+
+
 static int do_fflush(FILE *fp)
 {
        int ret = fflush(fp);
@@ -1487,6 +1492,49 @@ out:
        return ret;
 }
 
+static int open_wim_writable(WIMStruct *w, const char *path,
+                            bool trunc, bool readable)
+{
+       const char *mode;
+       int ret = 0;
+       if (trunc)
+               if (readable)
+                       mode = "w+b";
+               else
+                       mode = "wb";
+       else
+               mode = "r+b";
+
+       DEBUG("Opening `%s' read-write", path);
+       wimlib_assert(w->out_fp == NULL);
+       wimlib_assert(path != NULL);
+       w->out_fp = fopen(path, mode);
+       if (!w->out_fp) {
+               ERROR_WITH_ERRNO("Failed to open `%s' for writing", path);
+               return WIMLIB_ERR_OPEN;
+       }
+#if defined(HAVE_SYS_FILE_H) && defined(HAVE_FLOCK)
+       if (!trunc) {
+               ret = flock(fileno(w->out_fp), LOCK_EX | LOCK_NB);
+               if (ret != 0) {
+                       if (errno == EWOULDBLOCK) {
+                               ERROR("`%s' is already being modified "
+                                     "by another process", path);
+                               ret = WIMLIB_ERR_ALREADY_LOCKED;
+                               fclose(w->out_fp);
+                               w->out_fp = NULL;
+                       } else {
+                               WARNING("Failed to lock `%s': %s",
+                                       path, strerror(errno));
+                               ret = 0;
+                       }
+               }
+       }
+#endif
+       return ret;
+}
+
+
 static void close_wim_writable(WIMStruct *w)
 {
        if (w->out_fp) {