pstore/ftrace: Provide ftrace log merging routine

Move the ftrace log merging logic out of pstore/ram into pstore/ftrace
so other backends can use it, like pstore/zone.

Link: https://lore.kernel.org/lkml/20200510202436.63222-7-keescook@chromium.org/
Signed-off-by: Kees Cook <keescook@chromium.org>

1 files changed, 54 insertions, 0 deletions

diff --git a/fs/pstore/ftrace.c b/fs/pstore/ftrace.c
index bfbfc2698070..5c0450701293 100644
--- a/fs/pstore/ftrace.c
+++ b/fs/pstore/ftrace.c
@@ -16,6 +16,7 @@
 #include <linux/debugfs.h>
 #include <linux/err.h>
 #include <linux/cache.h>
+#include <linux/slab.h>
 #include <asm/barrier.h>
 #include "internal.h"
 
@@ -132,3 +133,56 @@ void pstore_unregister_ftrace(void)
 
 	debugfs_remove_recursive(pstore_ftrace_dir);
 }
+
+ssize_t pstore_ftrace_combine_log(char **dest_log, size_t *dest_log_size,
+				  const char *src_log, size_t src_log_size)
+{
+	size_t dest_size, src_size, total, dest_off, src_off;
+	size_t dest_idx = 0, src_idx = 0, merged_idx = 0;
+	void *merged_buf;
+	struct pstore_ftrace_record *drec, *srec, *mrec;
+	size_t record_size = sizeof(struct pstore_ftrace_record);
+
+	dest_off = *dest_log_size % record_size;
+	dest_size = *dest_log_size - dest_off;
+
+	src_off = src_log_size % record_size;
+	src_size = src_log_size - src_off;
+
+	total = dest_size + src_size;
+	merged_buf = kmalloc(total, GFP_KERNEL);
+	if (!merged_buf)
+		return -ENOMEM;
+
+	drec = (struct pstore_ftrace_record *)(*dest_log + dest_off);
+	srec = (struct pstore_ftrace_record *)(src_log + src_off);
+	mrec = (struct pstore_ftrace_record *)(merged_buf);
+
+	while (dest_size > 0 && src_size > 0) {
+		if (pstore_ftrace_read_timestamp(&drec[dest_idx]) <
+		    pstore_ftrace_read_timestamp(&srec[src_idx])) {
+			mrec[merged_idx++] = drec[dest_idx++];
+			dest_size -= record_size;
+		} else {
+			mrec[merged_idx++] = srec[src_idx++];
+			src_size -= record_size;
+		}
+	}
+
+	while (dest_size > 0) {
+		mrec[merged_idx++] = drec[dest_idx++];
+		dest_size -= record_size;
+	}
+
+	while (src_size > 0) {
+		mrec[merged_idx++] = srec[src_idx++];
+		src_size -= record_size;
+	}
+
+	kfree(*dest_log);
+	*dest_log = merged_buf;
+	*dest_log_size = total;
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(pstore_ftrace_combine_log);