[PATCH v3 0/9] io_uring: Initial support for {s,g}etsockopt commands

[Breno Leitao <leitao@debian.org>]

This patchset adds support for getsockopt (SOCKET_URING_OP_GETSOCKOPT)
and setsockopt (SOCKET_URING_OP_SETSOCKOPT) in io_uring commands.
SOCKET_URING_OP_SETSOCKOPT implements generic case, covering all levels
and optnames. SOCKET_URING_OP_GETSOCKOPT is limited, for now, to SOL_SOCKET
level, which seems to be the most common level parameter for get/setsockopt(2).

In order to keep the implementation (and tests) simple, some refactors were done
prior to the changes, as follows:

Patches 1-2: Modify the BPF hooks to support sockptr_t, so, these functions
become flexible enough to accept user or kernel pointers for optval/optlen.

Patch 3: Extract the core setsockopt() core function from __sys_setsockopt, so,
the code code could be reused by other callers, such as io_uring.

Patch 4: Pass compat mode to the file/socket callbacks.

Patch 5: Move io_uring helpers from io_uring_zerocopy_tx to a generic io_uring
headers. This simplify the testcase (last patch)

PS1: For getsockopt command, the optlen field is not a userspace
pointers, but an absolute value, so this is slightly different from
getsockopt(2) behaviour. The new optlen value is returned in cqe->res.

PS2: The userspace pointers need to be alive until the operation is
completed.

These changes were tested with a new test[1] in liburing, as also with
bpf/progs/sockopt test case, which is now adapted to run using both system
calls and io_uring commands.

[1] Link: https://github.com/leitao/liburing/blob/getsock/test/socket-getsetsock-cmd.c

RFC -> V1:
	* Copy user memory at io_uring subsystem, and call proto_ops
	  callbacks using kernel memory
	* Implement all the cases for SOCKET_URING_OP_SETSOCKOPT

V1 -> V2
	* Implemented the BPF part
	* Using user pointers from optval to avoid kmalloc in io_uring part.

V2 -> V3:
	* Break down __sys_setsockopt and reuse the core code, avoiding
	  duplicated code. This removed the requirement to export
	  sock_use_custom_sol_socket() as done in v2.
	* Added io_uring test to selftests/bpf/sockopt.
	* Fixed "compat" argument, by passing it to the issue_flags.

Breno Leitao (9):
  bpf: Leverage sockptr_t in BPF getsockopt hook
  bpf: Leverage sockptr_t in BPF setsockopt hook
  net/socket: Break down __sys_setsockopt
  io_uring/cmd: Pass compat mode in issue_flags
  selftests/net: Extract uring helpers to be reusable
  io_uring/cmd: Introduce SOCKET_URING_OP_GETSOCKOPT
  io_uring/cmd: Introduce SOCKET_URING_OP_SETSOCKOPT
  io_uring/cmd: BPF hook for getsockopt cmd
  selftests/bpf/sockopt: Add io_uring support