On Wed, Oct 10, 2012 at 06:07:33PM +0800, zwu.kernel@gmail.com wrote:

From: Zhi Yong Wu <redacted>

  FS_IOC_GET_HEAT_INFO: return a struct containing the various
metrics collected in btrfs_freq_data structs, and also return a
calculated data temperature based on those metrics. Optionally, retrieve
the temperature from the hot data hash list instead of recalculating it.

  FS_IOC_GET_HEAT_OPTS: return an integer representing the current
state of hot data tracking and migration:

0 = do nothing
1 = track frequency of access

  FS_IOC_SET_HEAT_OPTS: change the state of hot data tracking and
migration, as described above.

.....

+struct hot_heat_info {
+	__u64 avg_delta_reads;
+	__u64 avg_delta_writes;
+	__u64 last_read_time;
+	__u64 last_write_time;
+	__u32 num_reads;
+	__u32 num_writes;
+	__u32 temperature;
+	__u8 live;
+	char filename[PATH_MAX];

Don't put the filename in the ioctl and open the file in the kernel.
Have userspace open the file directly and issue the ioctl on the fd
that is returned.

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com