On 10/26/20 7:55 PM, Anand Jain wrote:

For mirrored raid profiles such as raid1, raid1c3, raid1c4, and raid10,
currently, btrfs use the PID method to determine which one of the
mirrored devices to use to read the block. However, the PID method is
not the best choice if the devices are heterogeneous in terms of type,
speed, and size, as we may end up reading from the slower device.

Export the function part_stat_read_all() so that the btrfs can determine
the device with the least average wait time to use.

Cc: linux-block@vger.kernel.org
Signed-off-by: Anand Jain <redacted>

You don't need this, it can be accomplished with part_stat_read, or any variety 
of the helpers in part_stat.h.  Thanks,

Josef