Merge pull request #7548 from yuyuyu101/librbd-avoid-memcpy

librbd: reduce mem copies to user-buffer during read

Reviewed-by: Jason Dillaman <dillaman@redhat.com>

diff --cc src/common/buffer.cc
Simple merge

diff --cc src/include/buffer.h
Simple merge

diff --cc src/librados/librados.cc
Simple merge