We want to first pass a mapping of unwritten extents to the blockdev_direct_IO
call. Then based upon the amount of bytes written we want to convert those
unwritten extents into written.

Currently if there is an extent on the last block the code will only set
EOF on ENOENT. In the case that the last block has an extent it wont go
to the next iteration due to iblock <= last. This then doesnt set the EOF
on the last block in these cases. We want to just allow the loop to keep
looping and rely on if (ext.start > last) to protect us from infinite loop.

In the buffered case page tail zeroing happens automatically.
In the O_DIRECT case it does not so we need to add it in our setattr
path just like EXT2. We want to zero the end of the block that contains
i_size during truncate, so we just call block_truncate_page in
set_inode_size.

Signed-off-by: Bryant G. Duffy-Ly <[email protected]>