mem: Update soft-dirty detection to work on -mm tree

The soft-dirty API has changed slightly -- now the bit in
question _is_ in pagemap file (not pagemap2) but to see it
we have to reset soft-dirty for anyone first.

Teach the kerndat soft-dirty checker this fact. The actual
pagemap reading code already knows select pagemap/pagemap2
file itself.
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

include/mem.h

 #ifndef __CR_MEM_H__
 #define __CR_MEM_H__
 struct vm_area_list;
+int do_task_reset_dirty_track(int pid);
 unsigned int dump_pages_args_size(struct vm_area_list *vmas);
 struct parasite_ctl;
 struct page_pipe;

kerndat.c

@@ -8,6 +8,7 @@
 
 #include "log.h"
 #include "kerndat.h"
+#include "mem.h"
 #include "asm/types.h"
 
 dev_t kerndat_shmem_dev;
@@ -69,9 +70,16 @@ int kerndat_get_dirty_track(void)
 		return ret;
 	}
 
-	map[0] = '\0';
-
 	pm2 = open("/proc/self/pagemap2", O_RDONLY);
+	if (pm2 < 0) {
+		/*
+		 * Kernel shows soft-dirty bits only if this soft-dirty
+		 * was at least once re-set. (this is to be removed in
+		 * a couple of kernel releases)
+		 */
+		do_task_reset_dirty_track(getpid());
+		pm2 = open("/proc/self/pagemap", O_RDONLY);
+	}
 	if (pm2 < 0) {
 		munmap(map, PAGE_SIZE);
 		if (errno == ENOENT) {
@@ -83,6 +91,8 @@ int kerndat_get_dirty_track(void)
 		return ret;
 	}
 
+	map[0] = '\0';
+
 	lseek(pm2, (unsigned long)map / PAGE_SIZE * sizeof(u64), SEEK_SET);
 	ret = read(pm2, &pmap, sizeof(pmap));
 	if (ret < 0){

mem.c

@@ -42,9 +42,6 @@ struct mem_snap_ctx {
 
 static int task_reset_dirty_track(int pid)
 {
-	int fd, ret;
-	char cmd[] = "4";
-
 	if (!opts.track_mem)
 		return 0;
 
@@ -54,7 +51,16 @@ static int task_reset_dirty_track(int pid)
 		return -1;
 	}
 
+	return do_task_reset_dirty_track(pid);
+}
+
+int do_task_reset_dirty_track(int pid)
+{
+	int fd, ret;
+	char cmd[] = "4";
+
 	pr_info("Reset %d's dirty tracking\n", pid);
+
 	fd = open_proc_rw(pid, "clear_refs");
 	if (fd < 0)
 		return -1;