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

[Mike Rapoport]

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.

> > ---
> >  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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> > CRIU at openvz.org
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> > 
> 
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