ioengine: Add fallocate ioengine

IO engine that does regular fallocate to simulate data transfer
as fio ioengine.
 DDIR_READ  does fallocate(,mode=FALLOC_FL_KEEP_SIZE,)
 DDIR_WRITE does fallocate(,mode=0) : fallocate with file extention
 DDIR_TRIM  does fallocate(FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE)

This engine may be useful to perform various tests:
1) Generation highly fragmentated files
2) Various fs stress testing in parallel with others io activity

Signed-off-by: Dmitry Monakhov <dmonakhov@openvz.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/HOWTO b/HOWTO
index 025443b..3eb5510 100644
--- a/HOWTO
+++ b/HOWTO
@@ -602,6 +602,8 @@
 				channel semantics (Send/Recv) for the
 				InfiniBand, RoCE and iWARP protocols.
 
+			falloc  Perform fallocate/punch_hole to files
+	
 			external Prefix to specify loading an external
 				IO engine object file. Append the engine
 				filename, eg ioengine=external:/tmp/foo.o