[CRIU] [PATCH 4/5] kdat: Cache kdat object into /run/criu.kdat (v2)

[Mike Rapoport]

On Wed, Apr 26, 2017 at 04:37:34PM +0300, Pavel Emelyanov wrote:
> Doing kerndat checks on every criu start is way too slow. We
> need some way to speed this checks up on a particular box.
> 
> As suggested by Andre, Dima and Mike let's try to keep the
> collected kdat bits into some tmpfs file. Keeping it on
> tmpfs would invaludate this cache on every machine reboot.
> 
> There have been many suggestions how to generate this file,
> my proposal is to create it once the kdat object is filled
> by criu, w/o any explicit command. Optionally we can add
> 'criu kdat --save|--drop' actions to manage this file.
> 
> v2:
> * don't ignore return code of write() (some glibcs complain)
> * unlink tmp file in case rename failed
> 
> Signed-off-by: Pavel Emelyanov <xemul at virtuozzo.com>
> ---
>  criu/include/kerndat.h |  6 ++++
>  criu/include/magic.h   |  7 +++++
>  criu/kerndat.c         | 85 +++++++++++++++++++++++++++++++++++++++++++++++++-
>  3 files changed, 97 insertions(+), 1 deletion(-)
> 
> diff --git a/criu/include/kerndat.h b/criu/include/kerndat.h
> index 6b621c6..b1722eb 100644
> --- a/criu/include/kerndat.h
> +++ b/criu/include/kerndat.h
> @@ -29,6 +29,12 @@ enum loginuid_func {
>  };
> 
>  struct kerndat_s {
> +	/*
> +	 * XXX: This structure is written AS IS into a tmpfs file,
> +	 * so any changes in it should result in changed KDAT_MAGIC
> +	 * value to avoid loading of bad kdat bits.
> +	 */
> +	u32 magic;
>  	dev_t shmem_dev;
>  	int last_cap;
>  	u64 zero_page_pfn;
> diff --git a/criu/include/magic.h b/criu/include/magic.h
> index 059d005..2297930 100644
> --- a/criu/include/magic.h
> +++ b/criu/include/magic.h
> @@ -116,4 +116,11 @@
>  #define STATS_MAGIC		0x57093306 /* Ostashkov */
>  #define IRMAP_CACHE_MAGIC	0x57004059 /* Ivanovo */
> 
> +/*
> + * Magic for kerndat_s structure. When changing, keep the
> + * old magics to avoid magic re-use.
> + */
> +
> +#define KDAT_MAGIC_1		0x57023458 /* Torzhok */
> +
>  #endif /* __CR_MAGIC_H__ */
> diff --git a/criu/kerndat.c b/criu/kerndat.c
> index 87a7b62..3aca1e4 100644
> --- a/criu/kerndat.c
> +++ b/criu/kerndat.c
> @@ -650,10 +650,93 @@ close:
>  	bclose(&f);
>  	return ret;
>  }
> +
> +#define KERNDAT_CACHE_FILE	"/run/criu.kdat"
> +#define KERNDAT_CACHE_FILE_TMP	"/run/.criu.kdat"

What about running criu as non-root user?

> +static int kerndat_try_load_cache(void)
> +{
> +	int fd, ret;
> +
> +	fd = open(KERNDAT_CACHE_FILE, O_RDONLY);
> +	if (fd < 0) {
> +		if (errno == ENOENT)
> +			return 1;
> +
> +		pr_perror("Can't load %s", KERNDAT_CACHE_FILE);
> +		return -1;
> +	}
> +
> +	ret = read(fd, &kdat, sizeof(kdat));
> +	if (ret < 0) {
> +		pr_perror("Can'r read kdat cache");
> +		return -1;
> +	}
> +
> +	close(fd);
> +
> +	if (ret != sizeof(kdat) || kdat.magic != KDAT_MAGIC_1) {
> +		pr_warn("Stale %s file\n", KERNDAT_CACHE_FILE);
> +		unlink(KERNDAT_CACHE_FILE);
> +		return 1;
> +	}
> +
> +	pr_info("Loaded criu.kdat cache\n");
> +	return 0;
> +}
> +
> +static int kerndat_save_cache(void)
> +{
> +	int fd, ret;
> +	struct statfs s;
> +
> +	fd = open(KERNDAT_CACHE_FILE_TMP, O_CREAT | O_EXCL | O_WRONLY, 0600);
> +	if (fd < 0) {
> +		/*
> +		 * It can happen that we race with some other criu
> +		 * instance. That's OK, just ignore this error and
> +		 * proceed.
> +		 */
> +		if (errno == EEXIST)
> +			return 0;
> +
> +		pr_perror("Can't save %s", KERNDAT_CACHE_FILE_TMP);
> +		return -1;
> +	}
> +
> +	if (fstatfs(fd, &s) < 0) {
> +		pr_perror("Can't statfs %s", KERNDAT_CACHE_FILE_TMP);
> +		return -1;
> +	}
> +
> +	if (s.f_type != TMPFS_MAGIC) {
> +		pr_warn("Can't keep criu.kdat on tempfs\n");
> +		close(fd);
> +		return 0;
> +	}
> +
> +	kdat.magic = KDAT_MAGIC_1;
> +	ret = write(fd, &kdat, sizeof(kdat));
> +	if (ret != sizeof(kdat))
> +		pr_warn("Kerndat cache writing failed.\n");
> +	close(fd);
> +
> +	ret = rename(KERNDAT_CACHE_FILE_TMP, KERNDAT_CACHE_FILE);
> +	if (ret < 0) {
> +		pr_perror("Can't save %s", KERNDAT_CACHE_FILE);
> +		unlink(KERNDAT_CACHE_FILE_TMP);
> +	}
> +	return ret;
> +}
> +
>  int kerndat_init(void)
>  {
>  	int ret;
> 
> +	ret = kerndat_try_load_cache();
> +	if (ret <= 0)
> +		return ret;
> +
>  	ret = check_pagemap();
>  	if (!ret)
>  		ret = kerndat_get_shmemdev();
> @@ -691,5 +774,5 @@ int kerndat_init(void)
>  	kerndat_lsm();
>  	kerndat_mmap_min_addr();
> 
> -	return ret;
> +	return kerndat_save_cache();
>  }
> -- 
> 2.5.5
> 
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