lock-emu.c: write lock holder's name into lock file

scripts/utils/lock-emu.c

@@ -3,13 +3,17 @@
 #include<stdlib.h>
 #include<sys/stat.h>
 #include<fcntl.h>
+#include<string.h>
+
+#define BUF_SIZE 32
 
 int tryLock(char * file){
-    return open(file, O_CREAT | O_EXCL);
+    return open(file, O_CREAT | O_EXCL | O_WRONLY, 0666);
 }
 
 int main(int argc, char* argv[]){
     int fd;
+	char user[BUF_SIZE];
 	if(argc < 2){
 	    printf("arguments are not right!\n");
 		exit(-1);
@@ -17,10 +21,20 @@ int main(int argc, char* argv[]){
 
     do{
         fd = tryLock(argv[1]);
-        if(fd > 0) break;
-		printf("there is a job running, waiting ...\n");
-		sleep(10);
-	} while(1);
+        if(fd > 0){
+            getlogin_r(user, BUF_SIZE);
+            write(fd, user, strlen(user));
+            break;
+        } else {
+            // someone is holding the lock...
+            fd = open(argv[1], O_RDONLY);
+            if(fd > 0){
+                read(fd, user, BUF_SIZE);
+                printf("%s is holding the lock, waiting ...\n", user);
+            }
+        }
+        sleep(10);
+    } while(1);
 
     return 0;
 }