I'd like to make this modification to accelerate pax(1) listing on
raw disk devices.  Please review.


I have a disk drive of removable media:

sd2 at scsibus0 targ 3 lun 0: <FUJITSU, M2513EL, 0020> SCSI2 7/optical removable
606 MB, 151 cyl, 64 head, 32 sec, 2048 bytes/sect x 310352 sectors

I use tar (or pax) on the raw device since NetBSD doesn't support
block devices (or filesystems) on non 512bytes/sectore disks.

Here, the listing on the device such as
	% pax -v -f /dev/rsd0c
is very slow, since pax uses read(2), not lseek(2), to
seek the next position on the device.

By the following changes, pax uses lseek() on devices
if the device is not a tape drive.

Is this OK?

Regards,
-- 
ITOH, Yasufumi <itoh@netbsd.org>

diff -uF^[a-zA-Z_][a-z 	A-Z0-9_]*(.*[^;]$ ar_io.c.orig ar_io.c
--- ar_io.c.orig	Mon Oct 25 08:16:15 1999
+++ ar_io.c	Wed Feb  9 21:13:52 2000
@@ -865,7 +865,7 @@ ar_fow(sksz, skipped)
 	 * number of physical blocks to skip (we do not know physical block
 	 * size at this point), so we must only read foward on tapes!
 	 */
-	if (artyp != ISREG) 
+	if (artyp == ISTAPE || artyp == ISPIPE)
 		return(0);
 
 	/*
@@ -878,13 +878,16 @@ ar_fow(sksz, skipped)
 		 * deal with the end of file (it will go to next volume by
 		 * itself)
 	 	 */
-		if ((mpos = cpos + sksz) > arsb.st_size) {
-			*skipped = arsb.st_size - cpos;
+		mpos = cpos + sksz;
+		if (artyp == ISREG && mpos > arsb.st_size)
 			mpos = arsb.st_size;
-		} else
-			*skipped = sksz;
-		if (lseek(arfd, mpos, SEEK_SET) >= 0)
+		if ((mpos = lseek(arfd, mpos, SEEK_SET)) >= 0) {
+			*skipped = mpos - cpos;
 			return(0);
+		}
+	} else {
+		if (artyp != ISREG)
+			return(0);		/* non-seekable device */
 	}
 	syswarn(1, errno, "Foward positioning operation on archive failed");
 	lstrval = -1;