not to mention a compile-time warning about the critical function
becoming unused, by replacing spec_bmap() with vop_stdbmap().
ntfs seems to have the same bug.
The factor for converting specfs block numbers to physical block
numbers is 1, but vop_stdbmap() uses the bogus factor
btodb(ap->a_vp->v_mount->mnt_stat.f_iosize), which is 16 for ffs with
the default block size of 8K. This factor is bogus even for vop_stdbmap()
-- the correct factor is related to the filesystem blocksize which is not
necessarily the same to the optimal i/o size. vop_stdbmap() was apparently
cloned from nfs where these sizes happen to be the same.
There may also be a problem with a_vp->v_mount being null. spec_bmap()
still checks for this, but I think the checks in specfs are dead code
which used to support block devices.
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