tmpfs: support SEEK_DATA and SEEK_HOLE

tmpfs: support SEEK_DATA and SEEK_HOLE

It's quite easy for tmpfs to scan the radix_tree to support llseek's new
SEEK_DATA and SEEK_HOLE options: so add them while the minutiae are still
on my mind (in particular, the !PageUptodate-ness of pages fallocated but
still unwritten).

But I don't know who actually uses SEEK_DATA or SEEK_HOLE, and whether it
would be of any use to them on tmpfs.  This code adds 92 lines and 752
bytes on x86_64 - is that bloat or worthwhile?

[[email protected]: fix warning with CONFIG_TMPFS=n]
Signed-off-by: Hugh Dickins <[email protected]>
Cc: Christoph Hellwig <[email protected]>
Cc: Josef Bacik <[email protected]>
Cc: Andi Kleen <[email protected]>
Cc: Andreas Dilger <[email protected]>
Cc: Dave Chinner <[email protected]>
Cc: Marco Stornelli <[email protected]>
Cc: Jeff liu <[email protected]>
Cc: Chris Mason <[email protected]>
Cc: Sunil Mushran <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>