libext2fs: force DIO alignment FreeBSD when operating on a block device

FreeBSD (and possibly BSD systems) requires that reads and writes to
block devices must be aligned, even when the O_DIRECT flag is not
specified.  Previously this was hard-coded to 512 bytes, but in order
to properly handle Advanced Format HDD's, query the BSD kernel to
determine the proper alignment to use.

Signed-off-by: Theodore Ts'o <tytso@mit.edu>
1 file changed