[stgt] [PATCH] Make virtual tapes more closely emulate physical ones

Jay Fenlason fenlason at redhat.com
Thu Jan 10 17:36:44 CET 2013

On my physical drive (a Sony AIT-2 drive, if it matters) when
userspace reads a file mark, it gets an EOF, and the tape is advanced
past the file mark so that a subsequent read will return data from the
next file on the tape.  With a virtual drive, the file mark is
sticky--reads continue to return EOF until the tape is manually
advanced with a FSF ioctl.  I wrote this quick patch to make the
virtual tape behave like my physical one.

I'm not sure about the sense_data_build hunk, but it matches the code
for fixed blocksize, and did no harm in my testing.

		-- JF

--- tgt-1.0.32/usr/bs_ssc.c.filemark	2012-09-30 18:39:21.000000000 -0400
+++ tgt-1.0.32/usr/bs_ssc.c	2013-01-09 15:32:43.000000000 -0500
@@ -325,6 +325,9 @@
 		if (h->blk_type == BLK_EOD)
 			sense_data_build(cmd, 0x40 | BLANK_CHECK,
+		else if (h->blk_type == BLK_FILEMARK)
+			ssc_sense_data_build(cmd, NO_SENSE | SENSE_FILEMARK,
+					     ASC_MARK, info, sizeof(info));
 			ssc_sense_data_build(cmd, NO_SENSE | 0x20,
@@ -339,8 +342,13 @@
-		if (!length)
+		if (!length) {
+			if (h->blk_type == BLK_FILEMARK) {
+				ret = skip_next_header(cmd->dev);
+				/* FIXME: ??? */
+			}
 			goto out;
+		}
 	ret = pread64(cmd->dev->fd, buf, length, h->curr + SSC_BLK_HDR_SIZE);
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