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

[Pavel Emelyanov]

On 03/26/2018 11:12 AM, Pavel Tikhomirov wrote:
> 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.

What's wrong with checking pid-reuse form stats sitting in workdir?

> 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);
>  	}
>  
>