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

[Pavel Emelyanov]

On 04/27/2017 09:11 AM, Adrian Reber wrote:
> On Thu, Apr 27, 2017 at 08:37:09AM +0300, Mike Rapoport wrote:
>> 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?

It, well, doesn't quite work by itself :) But yes, good catch, need to
address that too somehow.

> Could the location be Makefile dependent? For Fedora I would rather put
> the file in /run/criu/criu.kdat

Will do, thanks.

> and create the directory via tmpfiles.d?

I don't know what the tmpfiles.d is :) Would you explain, please?

-- Pavel