Reuses previous .unrecoverable files to help multistep recovering.

HISTORY

@@ -10,6 +10,9 @@ SnapRAID HISTORY
    But any new data added will be protected if you are using
    enough parity to fix both the silent error and at least
    another potential error.
+ * In "fix", if a previous attempt was made, resulting in a
+   .unrecoverable file, uses this file as starting point for the
+   new attempt.
  * New source code organization. The RAID engine is now
    an external component usable also in other projects.
 

TODO

@@ -5,15 +5,6 @@ This is the list of TODO items for SnapRAID.
 
 - Next
 
-* When renaming to .unrecoverable at now we always overwrite
-a previous copy losing partial, but potentially better, file recovery.
-Is it possible a better strategy ?
-Maybe we can rename the unrecoverable as the real file, if the real file
-is missing at the first open. This should ensure to always
-get better results if the file is hashed.
-Something like an incremental recovery, in case multiple fix commands
-are attempted.
-
 * Don't disable default 10d/12% if -p or -o is specified.
 But check that -p0 still work.
 
@@ -25,6 +16,14 @@ parity, but we can reuse the hash to check that the file was moved
 correctly.
 We can assume a file moved to another disk if it has the same name, size,
 and timestamp. Directory and inode can be different.
+This can be implemented with NEW blocks with HASH.
+In synch, we can do the hash check of such blocks before any other operation,
+before invalidating the parity of the moved files now converted in DELETED
+blocks.
+If an error is found, or we stop the sync, or we can use the parity of
+DELETED blocks to recover the missing ones.
+Missing blocks can be find by hash, using all the DELETED blocks with hash
+as search base.
 
 * Avoid to do optimized move operation if more files with
 same timestamp/size are present.

handle.c

@@ -45,32 +45,41 @@ int handle_create(struct snapraid_handle* handle, struct snapraid_file* file, in
 	handle->truncated = 0;
 	handle->created = 0;
 
-	/* open for read write */
-	/* O_SEQUENTIAL: opening in sequential mode in Windows */
+	/* flags for opening */
+	/* O_BINARY: open as binary file (Windows only) */
 	/* O_NOFOLLOW: do not follow links to ensure to open the real file */
-	flags = O_RDWR | O_BINARY | O_NOFOLLOW;
+	/* O_SEQUENTIAL: improve performance for sequential access (Windows only) */
+	flags = O_BINARY | O_NOFOLLOW;
 	if (!skip_sequential)
 		flags |= O_SEQUENTIAL;
-	handle->f = open(handle->path, flags);
 
-	/* if failed for missing permission */
-	if (handle->f == -1 && errno == EACCES) {
-		/* retry without requesting write permission */
-		flags = O_RDONLY | O_BINARY | O_NOFOLLOW;
-		if (!skip_sequential)
-			flags |= O_SEQUENTIAL;
-		handle->f = open(handle->path, flags);
+	/* open for read write */
+	handle->f = open(handle->path, flags | O_RDWR);
+
+	/* if failed for missing write permission */
+	if (handle->f == -1 && (errno == EACCES || errno == EROFS)) {
+		/* open for real-only */
+		handle->f = open(handle->path, flags | O_RDONLY);
 	}
 
 	/* if failed for missing file */
 	if (handle->f == -1 && errno == ENOENT) {
-		/* retry creating it */
-		flags = O_RDWR | O_CREAT | O_BINARY | O_NOFOLLOW;
-		if (!skip_sequential)
-			flags |= O_SEQUENTIAL;
-		/* mark it as created */
-		handle->created = 1;
-		handle->f = open(handle->path, flags, 0600);
+		char path_from[PATH_MAX];
+
+		/* check if exists a .unrecoverable copy, and rename to the real one */
+		pathprint(path_from , sizeof(path_from), "%s.unrecoverable", handle->path);
+
+		if (rename(path_from, handle->path) == 0) {
+			/* open for read write */
+			handle->f = open(handle->path, flags | O_RDWR);
+		} else {
+			/* create it */
+			handle->f = open(handle->path, flags | O_RDWR | O_CREAT, 0600);
+			if (handle->f != -1) {
+				/* mark it as created if really done */
+				handle->created = 1;
+			}
+		}
 	}
 
 	if (handle->f == -1) {
@@ -147,14 +156,16 @@ int handle_open(struct snapraid_handle* handle, struct snapraid_file* file, int
 	handle->truncated = 0;
 	handle->created = 0;
 
-	/* open for read */
-	/* O_SEQUENTIAL: opening in sequential mode in Windows */
+	/* flags for opening */
+	/* O_BINARY: open as binary file (Windows only) */
 	/* O_NOFOLLOW: do not follow links to ensure to open the real file */
-	/* O_NOATIME: do not change access time */
-	flags = O_RDONLY | O_BINARY | O_NOFOLLOW;
+	/* O_SEQUENTIAL: improve performance for sequential access (Windows only) */
+	flags = O_BINARY | O_NOFOLLOW;
 	if (!skip_sequential)
 		flags |= O_SEQUENTIAL;
-	handle->f = open_noatime(handle->path, flags);
+
+	/* open for read */
+	handle->f = open_noatime(handle->path, flags | O_RDONLY);
 	if (handle->f == -1) {
 		/* invalidate for error */
 		handle->file = 0;