Hi

A colleague of mine was having trouble copying files from a CD ISO that 
was mounted using the vnd device.  To make a longer story short, 
investigation has revealed the following:

In vnd.c, vnd->sc_size is set initially as:

		vnd->sc_size = btodb(vattr.va_size);	/* note truncation */

but then the lines:

			vnd->sc_geom.vng_ncylinders = vnd->sc_size / (64 * 32);

			/*
			 * Compute the actual size allowed by this geometry.
			 */
			geomsize = 32 * 64 * vnd->sc_geom.vng_ncylinders;

in vnd.c compute a 'geomsize' value that is smaller than the size of
the image (unless the size of the image falls on a 1MB boundary).  When 
'geomsize' is then assigned to 'vnd->sc_size' in the following:

		/*
		 * Truncate the size to that specified by
		 * the geometry.
		 * XXX Should we even bother with this?
		 */
		vnd->sc_size = geomsize;

vnd->sc_size is now smaller than it was before, and the last part of the image
(up to 1MB) ends up being inaccessible through the vnd.  For example, an iso 
image of 680624128 bytes (664672K) should have it's disklabel size computed
to be 1329344 blocks, whereas right now, that size is computed to be just 1329152.
( (664672*2)/(32*64)=649.09375 , and then 649*32*64=1329152 ).

The fix (from what I and others have concluded) is to remove the line:

                vnd->sc_size = geomsize;

since this would leave the size of the vnd at 1329344 blocks, and the 
disklabel would still have a reasonable geometry.

Comments?

Later...

Greg Oster