The "lustre/lustre_user.h" header has been in use for many years. The patch https://review.whamcloud.com/25246 "
LU-6401 uapi: migrate remaining uapi headers to uapi directory" moved the header to "linux/lustre/lustre_user.h" and left a stub "lustre/lustre_user.h" behind that generates a compiler warning that this header is deprecated.
However, no window was given between the introduction of the new header and the deprecation of the old header, which makes it difficult for applications to smoothly transition to the new header location. Also, installing Lustre headers into the "linux/" directory before Lustre is actually part of the kernel may potentially cause problems.
Disable the deprecation warning in the old header for several releases, until the new header location has been available for a good time and it is safe for applications to assume that it is available.