Adding lockfile.c

moving code from compile.c under an api so it can be reused.

lockfile.c

@@ -0,0 +1,74 @@
+
+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <errno.h>
+#include "lockfile.h"
+
+#define locked(x) ((x)->fd >= 0)
+
+int hold_lock(struct lockfile *lock, const char *filename, int force) {
+
+	int rc, mask = O_WRONLY | O_CREAT | O_TRUNC;
+
+	if (locked(lock))
+		return -1;
+
+	if (!force)
+		mask |= O_EXCL;
+
+	rc = snprintf(lock->name, sizeof(lock->name), "%s.lock", filename);
+	if (rc > sizeof(lock->name))
+		return -1;
+
+	lock->fd = open(lock->name, mask, 0600);
+	if (lock->fd < 0) {
+		if (errno == EEXIST) {
+			fprintf(stderr, "'%s' is locked\n", lock->name);
+		} else {
+			fprintf(stderr, "unable to create lockfile '%s'",
+				lock->name);
+		}
+		return -1;
+	}
+	return lock->fd;
+}
+
+int commit_lock(struct lockfile *lock) {
+
+	char target[4096];
+	int len;
+
+	if (!locked(lock))
+		return 0;
+
+	len = strlen(lock->name) - 5; /* .lock */
+
+	memcpy(target, lock->name, len);
+	target[len] = '\0';
+
+	if (rename(lock->name, target))
+		return -1;
+	lock->name[0] = '\0';
+	close(lock->fd);
+	lock->fd = -1;
+	return 0;
+}
+
+int release_lock(struct lockfile *lock) {
+
+	int rc;
+
+	if (!locked(lock))
+		return 0;
+	rc = unlink(lock->name);
+	if (rc == 0) {
+		lock->name[0] = '\0';
+		close(lock->fd);
+		lock->fd = -1;
+	}
+	return rc;
+}