[LU-13783] Support for linux kernel version 5.8

• Type: Task
• Resolution: Fixed
• Priority: Minor
• Fix Version/s: Lustre 2.16.0
• Assignee: Neil Brown
• Reporter: Neil Brown

Description

Now that Linux 5.8 is in the stablization phase it makes sense to support compiling against it.

There are several changes that we need to adjust for.  Some are easy, some require more work.

Linux 5.8:

• removes the fmr_pool API. 
• doesn't use mmap_sem directly any more - use "mmap_read_lock()" and similar
• kernel_setsockopt() has gone - need to use more direct access.
• rdma_reject() needs a new "reason for reject" arg
• NR_UNSTABLE_NFS has gone. Use NR_WRITEBACK instead
• 'dummy_context' in fscrypt has changed to "get_dummy_context", and fscrypt_dummy_context is now fsctype_get_dummy_context
• unexport kallsyms_lookup_name() and kallsyms_on_each_symbol()

 Also:

• __vmalloc() now only has 2 args.
• FIELD_SIZEOF is gone, use sizeof_field
• blkcipher is gone,, use skcipher
• cached rb_tree changes
• sysctl handlers like proc_doinvec now take a kernel pointer rather than a __user pointer

Issue Links

• is related to: LU-15407 fscrypt does not work on Ubuntu 5.8 kernel
• is related to: LU-14297 Can't compile lustre client against MLNX OFED-5.2-1.0.4 on Centos 7.8
• is related to: LU-14776 Ubuntu 20.04 HWE support
• is related to: LU-12511 Prepare lustre for adoption into the linux kernel
• is related to: LU-13761 MOFED 5.1 support