[PATCH] coredump: add core_pattern specifier for si_code

[Emanuele Rocca <emanuele.rocca@arm.com>]

The specifiers supported by core_pattern include the option to indicate the
signal number si_signo by using %s. Other than identifying which signal
generated a core dump (eg: 11 for SIGSEGV), it is useful to know the reason why
a certain signal was sent. The signal code si_code (eg: 2 for SEGV_ACCERR)
provides this information.

Adding the signal code to core_pattern can benefit in particular sysadmins who
pipe core dumps to user-space programs for later analysis. systemd-coredump(8)
is a notable example of such programs.

Signed-off-by: Emanuele Rocca <emanuele.rocca@arm.com>
---
 Documentation/admin-guide/sysctl/kernel.rst | 1 +
 fs/coredump.c                               | 5 +++++
 2 files changed, 6 insertions(+)

diff --git a/Documentation/admin-guide/sysctl/kernel.rst b/Documentation/admin-guide/sysctl/kernel.rst
index 9aed74e65cf4..20177bd94514 100644
--- a/Documentation/admin-guide/sysctl/kernel.rst
+++ b/Documentation/admin-guide/sysctl/kernel.rst
@@ -170,6 +170,7 @@ core_pattern
 	%d		dump mode, matches ``PR_SET_DUMPABLE`` and
 			``/proc/sys/fs/suid_dumpable``
 	%s		signal number
+	%n		signal code
 	%t		UNIX time of dump
 	%h		hostname
 	%e		executable filename (may be shortened, could be changed by prctl etc)
diff --git a/fs/coredump.c b/fs/coredump.c
index 29df8aa19e2e..e78a889fe34c 100644
--- a/fs/coredump.c
+++ b/fs/coredump.c
@@ -400,6 +400,11 @@ static bool coredump_parse(struct core_name *cn, struct coredump_params *cprm,
 				err = cn_printf(cn, "%d",
 						cprm->siginfo->si_signo);
 				break;
+			/* code of the signal that caused the coredump */
+			case 'n':
+				err = cn_printf(cn, "%d",
+						cprm->siginfo->si_code);
+				break;
 			/* UNIX time of coredump */
 			case 't': {
 				time64_t time;
-- 
2.47.3