[CRIU] [PATCH] pagemap: fix reading pages from socket for --remote case

[Pavel Emelyanov]

On 04/25/2017 01:38 PM, Mike Rapoport wrote:
> On Tue, Apr 25, 2017 at 08:56:19AM +0100, Rodrigo Bruno wrote:
>> Hi,
>>
>> 2017-04-24 18:00 GMT+01:00 Pavel Emelyanov <xemul at virtuozzo.com>:
>>
>>>>>
>>>>> Maybe it's better to introduce separate ->maybe_read_page callback for
>>> opts.remote case?
>>>>> This would let us localize the cache/proxy pages reading code in one
>>> place.
>>>>
>>>> Well, we could. E.g. something like the patch below (untested). Note that
>>>> we already have maybe_read_page_remote for the remote lazy restore case,
>>>> and, ideally, the cache/proxy and lazy cases should use the same code to
>>>> read pages.
>>>
>>> Yup. I like this patch :)
>>> Rodrigo, what do you think?
>>>
>>
>> I agree.
> 
> All right, below is the more formal version of the patch. I'd suggest to
> start with it to make --remote able to restore the memory. The next step
> related to --remote and the page-read would be to see if it's possible to
> use ASYNC with sockets, what should be refactored to enable it and how we
> reduce code and functionality duplication.
> 
>  
>>From 645c2f8e5afe090ee362d3225b97e2b5f1bc95cb Mon Sep 17 00:00:00 2001
> From: Mike Rapoport <rppt at linux.vnet.ibm.com>
> Date: Fri, 21 Apr 2017 17:29:10 +0300
> Subject: [CRIU][PATCH v3] pagemap: fix reading pages from socket for --remote case
> 
> When --remote option is specified, read_local_page tries to pread from a
> socket, and fails with "Illegal seek" error.
> Restore single pread call for regular image files case and introduce
> maybe_read_page_img_cache version of maybe_read_page method.
> 
> Generally-approved-by: Rodrigo Bruno <rbruno at gsd.inesc-id.pt>
> Signed-off-by: Mike Rapoport <rppt at linux.vnet.ibm.com>

Acked-by: Pavel Emelyanov <xemul at virtuozzo.com>

And Rodrigo was right telling that the posision in the page-read seem to
be not-needed, as we always access pages images linearly. But that's another
story, I guess we'll need to revisit this a bit later.

> ---
> v3: use different ->maybe_read_page method for --remote case
> v2: simplify call to pread in non-remote case, it does not need 'curr'
> 
>  criu/pagemap.c | 52 +++++++++++++++++++++++++++++++++++++++++-----------
>  1 file changed, 41 insertions(+), 11 deletions(-)
> 
> diff --git a/criu/pagemap.c b/criu/pagemap.c
> index 6c741b4..353c469 100644
> --- a/criu/pagemap.c
> +++ b/criu/pagemap.c
> @@ -255,7 +255,6 @@ static int read_local_page(struct page_read *pr, unsigned long vaddr,
>  {
>  	int fd = img_raw_fd(pr->pi);
>  	int ret;
> -	size_t curr = 0;
>  
>  	/*
>  	 * Flush any pending async requests if any not to break the
> @@ -265,15 +264,10 @@ static int read_local_page(struct page_read *pr, unsigned long vaddr,
>  		return -1;
>  
>  	pr_debug("\tpr%d-%u Read page from self %lx/%"PRIx64"\n", pr->pid, pr->id, pr->cvaddr, pr->pi_off);
> -	while (1) {
> -		ret = pread(fd, buf + curr, len - curr, pr->pi_off + curr);
> -		if (ret < 1) {
> -			pr_perror("Can't read mapping page %d", ret);
> -			return -1;
> -		}
> -		curr += ret;
> -		if (curr == len)
> -			break;
> +	ret = pread(fd, buf, len, pr->pi_off);
> +	if (ret != len) {
> +		pr_perror("Can't read mapping page %d", ret);
> +		return -1;
>  	}
>  
>  	if (opts.auto_dedup) {
> @@ -390,6 +384,40 @@ static int maybe_read_page_local(struct page_read *pr, unsigned long vaddr,
>  	return ret;
>  }
>  
> +static int maybe_read_page_img_cache(struct page_read *pr, unsigned long vaddr,
> +				     int nr, void *buf, unsigned flags)
> +{
> +	unsigned long len = nr * PAGE_SIZE;
> +	int fd = img_raw_fd(pr->pi);
> +	int ret;
> +	size_t curr = 0;
> +
> +	pr_debug("\tpr%d-%u Read page from self %lx/%"PRIx64"\n", pr->pid, pr->id, pr->cvaddr, pr->pi_off);
> +	while (1) {
> +		ret = read(fd, buf + curr, len - curr);
> +		if (ret < 0) {
> +			pr_perror("Can't read mapping page %d", ret);
> +			return -1;
> +		}
> +		curr += ret;
> +		if (curr == len)
> +			break;
> +	}
> +
> +	if (opts.auto_dedup) {
> +		ret = punch_hole(pr, pr->pi_off, len, false);
> +		if (ret == -1)
> +			return -1;
> +	}
> +
> +	if (ret == 0 && pr->io_complete)
> +		ret = pr->io_complete(pr, vaddr, nr);
> +
> +	pr->pi_off += len;
> +
> +	return ret;
> +}
> +
>  static int read_page_complete(int pid, unsigned long vaddr, int nr_pages, void *priv)
>  {
>  	int ret = 0;
> @@ -803,7 +831,9 @@ int open_page_read_at(int dfd, int pid, struct page_read *pr, int pr_flags)
>  	pr->id = ids++;
>  	pr->pid = pid;
>  
> -	if (remote)
> +	if (opts.remote)
> +		pr->maybe_read_page = maybe_read_page_img_cache;
> +	else if (remote)
>  		pr->maybe_read_page = maybe_read_page_remote;
>  	else
>  		pr->maybe_read_page = maybe_read_page_local;
>