MFC r281700:

MFC r281700:
Workaround bhyve virtual disks operation on top of GEOM providers.

GEOM does not support scatter/gather lists in its I/Os.  Such requests
are cut in pieces by physio(), that may be problematic, if those pieces
are not multiple of provider's sector size.  If such case is detected,
move the data through temporary sequential buffer.

git-svn-id: svn://svn.freebsd.org/base/stable/10@282307 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f