1 files changed, 90 insertions, 0 deletions
diff --git a/offset.c b/offset.c
new file mode 100644
index 0000000..e8be549
--- /dev/null
+++ b/offset.c
@@ -0,0 +1,90 @@
+/*  Copyright 2021 Alain Knaff.
+ *  This file is part of mtools.
+ *
+ *  Mtools is free software: you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation, either version 3 of the License, or
+ *  (at your option) any later version.
+ *
+ *  Mtools is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with Mtools.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ * filter to support filesystems stored at an offset into their image
+ */
+
+#include "sysincludes.h"
+#include "msdos.h"
+#include "mtools.h"
+#include "offset.h"
+
+typedef struct Offset_t {
+	struct Stream_t head;
+
+	mt_off_t offset;
+} Offset_t;
+
+static ssize_t offset_pread(Stream_t *Stream, char *buf,
+			    mt_off_t start, size_t len)
+{
+	DeclareThis(Offset_t);
+	return PREADS(This->head.Next, buf, start+This->offset, len);
+}
+
+static ssize_t offset_pwrite(Stream_t *Stream, char *buf,
+			     mt_off_t start, size_t len)
+{
+	DeclareThis(Offset_t);
+	return PWRITES(This->head.Next, buf, start+This->offset, len);
+}
+
+static Class_t OffsetClass = {
+	0,
+	0,
+	offset_pread,
+	offset_pwrite,
+	0, /* flush */
+	0, /* free */
+	set_geom_pass_through, /* set_geom */
+	0, /* get_data */
+	0, /* pre-allocate */
+	get_dosConvert_pass_through, /* dos convert */
+	0, /* discard */
+};
+
+Stream_t *OpenOffset(Stream_t *Next, struct device *dev, off_t offset,
+		     char *errmsg, mt_off_t *maxSize) {
+	Offset_t *This;
+
+	This = New(Offset_t);
+	if (!This){
+		printOom();
+		return 0;
+	}
+	memset((void*)This, 0, sizeof(Offset_t));
+	init_head(&This->head, &OffsetClass, Next);
+
+	This->offset = offset;
+
+	if(maxSize) {
+		if(This->offset > *maxSize) {
+			if(errmsg)
+				sprintf(errmsg,"init: Big disks not supported");
+			goto exit_0;
+		}
+
+		*maxSize -= This->offset;
+	}
+
+	if(adjust_tot_sectors(dev, This->offset, errmsg) < 0)
+		goto exit_0;
+
+	return &This->head;
+ exit_0:
+	Free(This);
+	return NULL;
+}