[CRIU] [PATCH] stats/pid-reuse: put stats to image directory instead of cwd

[Pavel Tikhomirov]

Statistics for a special dump/pre-dump/restore action should be
collected in the images directory of these action. We need these for
pid-reuse detection as we need to read the stats of parent predump.

Now then work-dir option is set statistics image is put to the work-dir
and on each iteration these image will replace previos image.

For backward compatibility with older versions of p.haul create a
symlink in cwd so that p.haul still has access to the latest stats
image. Yet I plan to make p.haul work with stats through images dir.

https://jira.sw.ru/browse/PSBM-82864
Signed-off-by: Pavel Tikhomirov <ptikhomirov at virtuozzo.com>
---
 criu/stats.c | 61 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 60 insertions(+), 1 deletion(-)

diff --git a/criu/stats.c b/criu/stats.c
index d344ad336..2c0f8bda4 100644
--- a/criu/stats.c
+++ b/criu/stats.c
@@ -1,6 +1,7 @@
 #include <unistd.h>
 #include <fcntl.h>
 #include <sys/time.h>
+#include <sys/stat.h>
 #include "int.h"
 #include "atomic.h"
 #include "cr_options.h"
@@ -157,6 +158,53 @@ static void display_stats(int what, StatsEntry *stats)
 		return;
 }
 
+static int fd_to_path(int fd, char *buf, int size) {
+	char proc_self_fd_path[PATH_MAX];
+	int ret;
+
+	if (snprintf(proc_self_fd_path, PATH_MAX, "/proc/self/fd/%d", fd) < 0) {
+		pr_perror("Failed to format /proc/self/fd/* path");
+		return -1;
+	}
+
+	ret = readlink(proc_self_fd_path, buf, size-1);
+	if (ret < 0) {
+		pr_perror("Failed to readlink %s path", proc_self_fd_path);
+		return -1;
+	}
+	buf[ret] = '\0';
+
+	return 0;
+}
+
+static void symlink_stats(char *target, char *name)
+{
+	char link_path[PATH_MAX];
+	struct stat st;
+	int ret;
+
+	if (snprintf(link_path, PATH_MAX, imgset_template[CR_FD_STATS].fmt, name) < 0)
+		goto exit;
+
+	ret = lstat(link_path, &st);
+	if (ret == -1 && errno != ENOENT)
+		goto exit;
+	else if (ret == 0) {
+		/* Real image occupies these location, no symlink needed */
+		if (!S_ISLNK(st.st_mode))
+			return;
+
+		/* Unlink symlink of previous iteration */
+		if (unlink(link_path) == -1)
+			goto exit;
+	}
+
+	if(!symlink(target, link_path))
+		return;
+exit:
+	pr_warn("Error when trying to create stats symlink");
+}
+
 void write_stats(int what)
 {
 	StatsEntry stats = STATS_ENTRY__INIT;
@@ -203,9 +251,20 @@ void write_stats(int what)
 	} else
 		return;
 
-	img = open_image_at(AT_FDCWD, CR_FD_STATS, O_DUMP, name);
+	img = open_image(CR_FD_STATS, O_DUMP, name);
 	if (img) {
+		char image_path[PATH_MAX];
+
 		pb_write_one(img, &stats, PB_STATS);
+
+		/*
+		 * Backward compatibility: old p.haul whants to read stats
+		 * from working directory, but not from images directory, so
+		 * create a symlink for it.
+		 */
+		if (!fd_to_path(img->fd, image_path, PATH_MAX))
+			symlink_stats(image_path, name);
+
 		close_image(img);
 	}
 
-- 
2.14.3