Merge branch 'add support for writable bare tracepoint'

Hou Tao says:

====================

From: Hou Tao <houtao1@huawei.com>

Hi,

The patchset series supports writable context for bare tracepoint.

The main idea comes from patchset "writable contexts for bpf raw
tracepoints" [1], but it only supports normal tracepoint with
associated trace event under tracefs. Now we have one use case
in which we add bare tracepoint in VFS layer, and update
file::f_mode for specific files. The reason using bare tracepoint
is that it doesn't form a ABI and we can change it freely. So
add support for it in BPF.

Comments are always welcome.

[1]: https://lore.kernel.org/lkml/20190426184951.21812-1-mmullins@fb.com

Change log:
v5:
 * rebased on bpf-next
 * patch 1: add Acked-by tag
 * patch 2: handle invalid section name, make prefixes array being const

v4: https://www.spinics.net/lists/bpf/msg47021.html
 * rebased on bpf-next
 * update patch 2 to add support for writable raw tracepoint attachment
   in attach_raw_tp().
 * update patch 3 to add Acked-by tag

v3: https://www.spinics.net/lists/bpf/msg46824.html
  * use raw_tp.w instead of raw_tp_writable as section
    name of writable tp
  * use ASSERT_XXX() instead of CHECK()
  * define a common macro for "/sys/kernel/bpf_testmod"

v2: https://www.spinics.net/lists/bpf/msg46356.html
  * rebase on bpf-next tree
  * address comments from Yonghong Song
  * rename bpf_testmode_test_writable_ctx::ret as early_ret to reflect
    its purpose better.

v1: https://www.spinics.net/lists/bpf/msg46221.html
====================

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>