This patch fix behaviour in such test scenario:

  lseek(fd, BIG_OFFSET)
  write(fd, buf, sizeof(buf))
  truncate(BIG_OFFSET)
  truncate(BIG_OFFSET + sizeof(buf))
  read(fd, buf...)

Because of if file big enough(BIG_OFFSET) we start allocate space by block,
ordinary block size > page size, so we should zeroize the rest of block in
truncate(except last framgnet, about which VFS should care), to not get
garbage, when we extend file.

Also patch corrects conversion from pointer to block to physical block number,
this helps in case of not common used UFS types.

And add to debug output inode number.
Signed-off-by: NEvgeniy Dushistov <dushistov@mail.ru>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>