BACKPORT: coredump: add %f for executable filename

The document reads "%e" should be "executable filename" while actually it
could be changed by things like pr_ctl PR_SET_NAME.  People who uses "%e"
in core_pattern get surprised when they find out they get thread name
instead of executable filename.

This is either a bug of document or a bug of code.  Since the behavior of
"%e" is there for long time, it could bring another surprise for users if
we "fix" the code.

So we just "fix" the document.  And more, for users who really need the
"executable filename" in core_pattern, we introduce a new "%f" for the
real executable filename.  We already have "%E" for executable path in
kernel, so just reuse most of its code for the new added "%f" format.

Signed-off-by: Lepton Wu <ytht.net@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Link: http://lkml.kernel.org/r/20200701031432.2978761-1-ytht.net@gmail.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
(cherry picked from commit f38c85f1ba6902e4e2e2bf1b84edf065a904cdeb)

  - backport:
     Fix conflicts in fs/coredump.c and update Documentation/sysctl/kernel.txt
BUG=chromium:1115730
TEST=CQ

Change-Id: I4c8067de34bb7cff39905eb1008701cafc6ea3b2
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/kernel/+/2353891
Commit-Queue: Lepton Wu <lepton@chromium.org>
Commit-Queue: Guenter Roeck <groeck@chromium.org>
Tested-by: Lepton Wu <lepton@chromium.org>
Auto-Submit: Lepton Wu <lepton@chromium.org>
Reviewed-by: Guenter Roeck <groeck@chromium.org>
2 files changed