In msdosfs_read(), mainly reorder the main loop to the same order as in
ffs_read().
In msdosfs_write() and extendfile(), use vfs_bio_clrbuf() instead of
clrbuf(). I think this just just a bogus optimization, but ffs always
does it and msdosfs already did it in one place, and it is what I've
tested.
In msdosfs_write(), merge good bits from a comment in ffs_write(), and
fix 1 style bug.
In the main comment for msdosfs_pcbmap(), improve wording and catch
up with 13 years of changes in the function. This comment belongs in
VOP_BMAP.9 but that doesn't exist.
In msdosfs_bmap(), return EFBIG if the requested cluster number is out
of bounds instead of blindly truncating it, and fix many style bugs.
Approved by: re (hrs)
d34b0a1bac