printk: introduce a kmsg_dump iterator

Rather than storing the iterator information in the registered
kmsg_dumper structure, create a separate iterator structure. The
kmsg_dump_iter structure can reside on the stack of the caller, thus
allowing lockless use of the kmsg_dump functions.

Update code that accesses the kernel logs using the kmsg_dumper
structure to use the new kmsg_dump_iter structure. For kmsg_dumpers,
this also means adding a call to kmsg_dump_rewind() to initialize
the iterator.

All this is in preparation for removal of @logbuf_lock.

Signed-off-by: John Ogness <john.ogness@linutronix.de>
Reviewed-by: Kees Cook <keescook@chromium.org> # pstore
Reviewed-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20210303101528.29901-13-john.ogness@linutronix.de

1 files changed, 20 insertions, 16 deletions

diff --git a/include/linux/kmsg_dump.h b/include/linux/kmsg_dump.h
index 84eaa2090efa..36c8c57e1051 100644
--- a/include/linux/kmsg_dump.h
+++ b/include/linux/kmsg_dump.h
@@ -30,41 +30,45 @@ enum kmsg_dump_reason {
 };
 
 /**
+ * struct kmsg_dump_iter - iterator for retrieving kernel messages
+ * @cur_seq:	Points to the oldest message to dump
+ * @next_seq:	Points after the newest message to dump
+ */
+struct kmsg_dump_iter {
+	u64	cur_seq;
+	u64	next_seq;
+};
+
+/**
  * struct kmsg_dumper - kernel crash message dumper structure
  * @list:	Entry in the dumper list (private)
  * @dump:	Call into dumping code which will retrieve the data with
  * 		through the record iterator
  * @max_reason:	filter for highest reason number that should be dumped
  * @registered:	Flag that specifies if this is already registered
- * @cur_seq:	Points to the oldest message to dump
- * @next_seq:	Points after the newest message to dump
  */
 struct kmsg_dumper {
 	struct list_head list;
 	void (*dump)(struct kmsg_dumper *dumper, enum kmsg_dump_reason reason);
 	enum kmsg_dump_reason max_reason;
 	bool registered;
-
-	/* private state of the kmsg iterator */
-	u64 cur_seq;
-	u64 next_seq;
 };
 
 #ifdef CONFIG_PRINTK
 void kmsg_dump(enum kmsg_dump_reason reason);
 
-bool kmsg_dump_get_line_nolock(struct kmsg_dumper *dumper, bool syslog,
+bool kmsg_dump_get_line_nolock(struct kmsg_dump_iter *iter, bool syslog,
 			       char *line, size_t size, size_t *len);
 
-bool kmsg_dump_get_line(struct kmsg_dumper *dumper, bool syslog,
+bool kmsg_dump_get_line(struct kmsg_dump_iter *iter, bool syslog,
 			char *line, size_t size, size_t *len);
 
-bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
+bool kmsg_dump_get_buffer(struct kmsg_dump_iter *iter, bool syslog,
 			  char *buf, size_t size, size_t *len_out);
 
-void kmsg_dump_rewind_nolock(struct kmsg_dumper *dumper);
+void kmsg_dump_rewind_nolock(struct kmsg_dump_iter *iter);
 
-void kmsg_dump_rewind(struct kmsg_dumper *dumper);
+void kmsg_dump_rewind(struct kmsg_dump_iter *iter);
 
 int kmsg_dump_register(struct kmsg_dumper *dumper);
 
@@ -76,30 +80,30 @@ static inline void kmsg_dump(enum kmsg_dump_reason reason)
 {
 }
 
-static inline bool kmsg_dump_get_line_nolock(struct kmsg_dumper *dumper,
+static inline bool kmsg_dump_get_line_nolock(struct kmsg_dump_iter *iter,
 					     bool syslog, const char *line,
 					     size_t size, size_t *len)
 {
 	return false;
 }
 
-static inline bool kmsg_dump_get_line(struct kmsg_dumper *dumper, bool syslog,
+static inline bool kmsg_dump_get_line(struct kmsg_dump_iter *iter, bool syslog,
 				const char *line, size_t size, size_t *len)
 {
 	return false;
 }
 
-static inline bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
+static inline bool kmsg_dump_get_buffer(struct kmsg_dump_iter *iter, bool syslog,
 					char *buf, size_t size, size_t *len)
 {
 	return false;
 }
 
-static inline void kmsg_dump_rewind_nolock(struct kmsg_dumper *dumper)
+static inline void kmsg_dump_rewind_nolock(struct kmsg_dump_iter *iter)
 {
 }
 
-static inline void kmsg_dump_rewind(struct kmsg_dumper *dumper)
+static inline void kmsg_dump_rewind(struct kmsg_dump_iter *iter)
 {
 }