pstore/platform: Pass max_reason to kmesg dump

Add a new member to struct pstore_info for passing information about
kmesg dump maximum reason. This allows a finer control of what kmesg
dumps are sent to pstore storage backends.

Those backends that do not explicitly set this field (keeping it equal to
0), get the default behavior: store only Oopses and Panics, or everything
if the printk.always_kmsg_dump boot param is set.

Signed-off-by: Pavel Tatashin <pasha.tatashin@soleen.com>
Link: https://lore.kernel.org/lkml/20200515184434.8470-5-keescook@chromium.org/
Co-developed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Kees Cook <keescook@chromium.org>

fs/pstore/platform.c

@@ -595,8 +595,10 @@ int pstore_register(struct pstore_info *psi)
 
 	pstore_get_records(0);
 
-	if (psi->flags & PSTORE_FLAGS_DMESG)
+	if (psi->flags & PSTORE_FLAGS_DMESG) {
+		pstore_dumper.max_reason = psinfo->max_reason;
 		pstore_register_kmsg();
+	}
 	if (psi->flags & PSTORE_FLAGS_CONSOLE)
 		pstore_register_console();
 	if (psi->flags & PSTORE_FLAGS_FTRACE)

include/linux/pstore.h

@@ -96,6 +96,12 @@ struct pstore_record {
  *
  * @read_mutex:	serializes @open, @read, @close, and @erase callbacks
  * @flags:	bitfield of frontends the backend can accept writes for
+ * @max_reason:	Used when PSTORE_FLAGS_DMESG is set. Contains the
+ *		kmsg_dump_reason enum value. KMSG_DUMP_UNDEF means
+ *		"use existing kmsg_dump() filtering, based on the
+ *		printk.always_kmsg_dump boot param" (which is either
+ *		KMSG_DUMP_OOPS when false, or KMSG_DUMP_MAX when
+ *		true); see printk.always_kmsg_dump for more details.
  * @data:	backend-private pointer passed back during callbacks
  *
  * Callbacks:
@@ -179,6 +185,7 @@ struct pstore_info {
 	struct mutex	read_mutex;
 
 	int		flags;
+	int		max_reason;
 	void		*data;
 
 	int		(*open)(struct pstore_info *psi);