[CRIU] [PATCH 1/3] page-read: Do not lseek file to get its current position

[Pavel Emelyanov]

On 11/12/2016 04:35 PM, Mike Rapoport wrote:
> On Wed, Nov 09, 2016 at 08:39:17PM +0200, Mike Rapoport wrote:
>> On Mon, Nov 07, 2016 at 07:02:50PM +0300, Pavel Emelyanov wrote:
>>> It's already written into page_read->pi_off, so just use one.
>>>
>>> Signed-off-by: Pavel Emelyanov <xemul at virtuozzo.com>
>>
>> Acked-by: Mike Rapoport <rppt at linux.vnet.ibm.com>
>  
> Actually, not...
> For cases when pages*img is randomly accessed, i.e. dedup and lazy-pages,
> we still have to maintain actual position on the pages*img file and that
> requires lseek. We can avoid lseek's for sequential reads if, say, we'll
> add another pi_off_something to track actual position in the pages*img.

Don't we ->reset the page-read in such cases? I thought we did...

>>> ---
>>>  criu/pagemap.c | 11 +++++------
>>>  1 file changed, 5 insertions(+), 6 deletions(-)
>>>
>>> diff --git a/criu/pagemap.c b/criu/pagemap.c
>>> index 105ad59..cfc9659 100644
>>> --- a/criu/pagemap.c
>>> +++ b/criu/pagemap.c
>>> @@ -260,23 +260,22 @@ static int read_pagemap_page(struct page_read *pr, unsigned long vaddr, int nr,
>>>  		BUG();
>>>  	} else {
>>>  		int fd = img_raw_fd(pr->pi);
>>> -		off_t current_vaddr = lseek(fd, pr->pi_off, SEEK_SET);
>>>
>>> -		pr_debug("\tpr%u Read page from self %lx/%"PRIx64"\n", pr->id, pr->cvaddr, current_vaddr);
>>> -		ret = read(fd, buf, len);
>>> +		pr_debug("\tpr%u Read page from self %lx/%"PRIx64"\n", pr->id, pr->cvaddr, pr->pi_off);
>>> +		ret = pread(fd, buf, len, pr->pi_off);
>>>  		if (ret != len) {
>>>  			pr_perror("Can't read mapping page %d", ret);
>>>  			return -1;
>>>  		}
>>>
>>> -		pr->pi_off += len;
>>> -
>>>  		if (opts.auto_dedup) {
>>> -			ret = punch_hole(pr, current_vaddr, len, false);
>>> +			ret = punch_hole(pr, pr->pi_off, len, false);
>>>  			if (ret == -1) {
>>>  				return -1;
>>>  			}
>>>  		}
>>> +
>>> +		pr->pi_off += len;
>>>  	}
>>>
>>>  	pr->cvaddr += len;
>>> -- 
>>> 2.1.4
>>>
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>>
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>>
> 
> .
>