blktrace: support per-partition tracing for ftrace plugin
blktrace: support per-partition tracing for ftrace plugin

The previous patch adds support to trace a single partition for
relay+ioctl blktrace, and this patch is for ftrace plugin blktrace:

  # echo 1 > /sys/block/sda/sda7/enable
  # cat start_lba
  102398373
  # cat end_lba
  102703545

Signed-off-by: Li Zefan <5dc16b054e85ffba6c8d314d8e55ae95dcab12a5@cn.fujitsu.com>
Acked-by: "Theodore Ts'o" <4ed386e0495d3e109932df055831d9ec2f824927@mit.edu>
Cc: Arnaldo Carvalho de Melo <293abb6b76d7791c0732cc517d38c4b5c734b87f@redhat.com>
Cc: Shawn Du <d6ad5410ad947064051057e47dbddd9e97d8f4bb@gmail.com>
Cc: Jens Axboe <165ab144a3ccfd9429d5c6466b275f24fafdb114@oracle.com>
LKML-Reference: <2e4feca4ee52d09ec6e768a3d9882e8474a19a94@cn.fujitsu.com>
Signed-off-by: Ingo Molnar <9dbbbf0688fedc85ad4da37637f1a64b8c718ee2@elte.hu>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas