http://www.ecma-international.org/publications/files/ECMA-ST/Ecma-119.pdf

page 19:


Volume Space Size (BP 81 to 88) 
This field shall specify as a 32-bit number the number of Logical Blocks in which the Volume Space of the 
volume is recorded. 
This field shall be recorded according to 7.3.3.

Reference: /n/sources/patch/applied/mkisovolsize
Date: Fri Jun 28 22:23:59 CES 2013
Signed-off-by: paurea@lsub.org

--- /sys/src/cmd/disk/9660/dump9660.c	Fri Jun 28 22:23:36 2013
+++ /sys/src/cmd/disk/9660/dump9660.c	Fri Jun 28 22:23:33 2013
@@ -322,11 +322,11 @@
 		 * Patch in root directories.
 		 */
 		setroot(cd, cd->iso9660pvd, iroot.block, iroot.length);
-		setvolsize(cd, cd->iso9660pvd, (vlong)cd->nextblock * Blocksize);
+		setvolsize(cd, cd->iso9660pvd, (vlong)cd->nextblock);
 		if(cd->flags & CDjoliet){
 			setroot(cd, cd->jolietsvd, jroot.block, jroot.length);
 			setvolsize(cd, cd->jolietsvd,
-				(vlong)cd->nextblock * Blocksize);
+				(vlong)cd->nextblock);
 		}
 	}else{
 		/*
@@ -356,11 +356,11 @@
 		 * Patch in new root directory entry.
 		 */
 		setroot(cd, cd->iso9660pvd, idumproot.block, idumproot.length);
-		setvolsize(cd, cd->iso9660pvd, (vlong)cd->nextblock * Blocksize);
+		setvolsize(cd, cd->iso9660pvd, (vlong)cd->nextblock);
 		if(cd->flags & CDjoliet){
 			setroot(cd, cd->jolietsvd, jdumproot.block, jdumproot.length);
 			setvolsize(cd, cd->jolietsvd,
-				(vlong)cd->nextblock * Blocksize);
+				(vlong)cd->nextblock);
 		}
 	}
 	writepathtables(cd);