From: Eric Biggers <ebiggers3@gmail.com>
Date: Thu, 22 Nov 2012 04:42:59 +0000 (-0600)
Subject: Acquire advisory lock when doing a read-write mount
X-Git-Tag: v1.2.0~16
X-Git-Url: https://wimlib.net/git/?p=wimlib;a=commitdiff_plain;h=0abf993ee42a46139cc447f0cc610c1b3a0122dd

Acquire advisory lock when doing a read-write mount
---

diff --git a/src/mount.c b/src/mount.c
index e130b084..1290bd54 100644
--- a/src/mount.c
+++ b/src/mount.c
@@ -1915,6 +1915,12 @@ WIMLIBAPI int wimlib_mount_image(WIMStruct *wim, int image, const char *dir,
 		goto out;
 	}
 
+	if (mount_flags & WIMLIB_MOUNT_FLAG_READWRITE) {
+		ret = lock_wim(wim->fp, wim->filename);
+		if (ret != 0)
+			goto out;
+	}
+
 	if (!(mount_flags & (WIMLIB_MOUNT_FLAG_STREAM_INTERFACE_NONE |
 		       WIMLIB_MOUNT_FLAG_STREAM_INTERFACE_XATTR |
 		       WIMLIB_MOUNT_FLAG_STREAM_INTERFACE_WINDOWS)))
diff --git a/src/wimlib.h b/src/wimlib.h
index 0b0f04bf..0ba59d45 100644
--- a/src/wimlib.h
+++ b/src/wimlib.h
@@ -1399,6 +1399,11 @@ extern int wimlib_join(const char **swms, unsigned num_swms,
  * 	directory in the future.  Set to @c NULL.
  *
  * @return 0 on success; nonzero on error.
+ * @retval ::WIMLIB_ERR_ALREADY_LOCKED
+ * 	A read-write mount was requested, but an an exclusive advisory lock on
+ * 	the on-disk WIM file could not be acquired because another thread or
+ * 	process has mounted an image from the WIM read-write or is currently
+ * 	modifying the WIM in-place.
  * @retval ::WIMLIB_ERR_DECOMPRESSION
  * 	Could not decompress the metadata resource for @a image in @a wim.
  * @retval ::WIMLIB_ERR_FUSE
@@ -1577,10 +1582,10 @@ extern int wimlib_open_wim(const char *wim_file, int open_flags,
  * @return 0 on success; nonzero on error.  This function may return any value
  * returned by wimlib_write() as well as the following error codes:
  * @retval ::WIMLIB_ERR_ALREADY_LOCKED
- * 	The append-only overwrite mode was going to be used, but an exclusive
- * 	advisory lock on the on-disk WIM file could not be acquired, probably
- * 	because another thread or process was calling wimlib_overwrite() on the
- * 	same underlying on-disk file at the same time.
+ * 	The WIM was going to be modifien in-place (with no temporary file), but
+ * 	an exclusive advisory lock on the on-disk WIM file could not be acquired
+ * 	because another thread or process has mounted an image from the WIM
+ * 	read-write or is currently modifying the WIM in-place.
  * @retval ::WIMLIB_ERR_NO_FILENAME
  * 	@a wim corresponds to a WIM created with wimlib_create_new_wim() rather
  * 	than a WIM read with wimlib_open_wim().
diff --git a/src/wimlib_internal.h b/src/wimlib_internal.h
index 19497834..9b8c6b72 100644
--- a/src/wimlib_internal.h
+++ b/src/wimlib_internal.h
@@ -545,5 +545,14 @@ extern int begin_write(WIMStruct *w, const char *path, int write_flags);
 extern int finish_write(WIMStruct *w, int image, int write_flags,
 			wimlib_progress_func_t progress_func);
 
+#if defined(HAVE_SYS_FILE_H) && defined(HAVE_FLOCK)
+extern int lock_wim(FILE *fp, const char *path);
+#else
+static inline int lock_wim(FILE *fp, const char *path)
+{
+	return 0;
+}
+#endif
+
 #endif /* _WIMLIB_INTERNAL_H */
 
diff --git a/src/write.c b/src/write.c
index 773de0b7..e441b584 100644
--- a/src/write.c
+++ b/src/write.c
@@ -1492,6 +1492,29 @@ out:
 	return ret;
 }
 
+#if defined(HAVE_SYS_FILE_H) && defined(HAVE_FLOCK)
+int lock_wim(FILE *fp, const char *path)
+{
+	int ret = 0;
+	if (fp) {
+		ret = flock(fileno(fp), LOCK_EX | LOCK_NB);
+		if (ret != 0) {
+			if (errno == EWOULDBLOCK) {
+				ERROR("`%s' is already being modified or has been "
+				      "mounted read-write\n"
+				      "        by another process!", path);
+				ret = WIMLIB_ERR_ALREADY_LOCKED;
+			} else {
+				WARNING("Failed to lock `%s': %s",
+					path, strerror(errno));
+				ret = 0;
+			}
+		}
+	}
+	return ret;
+}
+#endif
+
 static int open_wim_writable(WIMStruct *w, const char *path,
 			     bool trunc, bool readable)
 {
@@ -1513,24 +1536,13 @@ static int open_wim_writable(WIMStruct *w, const char *path,
 		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 (trunc) {
+		ret = lock_wim(w->out_fp, path);
 		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;
-			}
+			fclose(w->out_fp);
+			w->out_fp = NULL;
 		}
 	}
-#endif
 	return ret;
 }