[CRIU] [PATCH v2] restore: Fetch mmap_minimal_address runtime

[Pavel Emelyanov]

On 12/07/2016 03:43 PM, Cyrill Gorcunov wrote:
> From: Cyrill Gorcunov <gorcunov at virtuozzo.com>
> 
> We assume that mmap_minimal_address with non-default
> setting is not widespread but it's not true. Instead
> lets fetch this setting runtime. For speed sake the value
> is cached.
> 
> Signed-off-by: Cyrill Gorcunov <gorcunov at virtuozzo.com>
> ---
>  criu/cr-restore.c | 39 ++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 38 insertions(+), 1 deletion(-)
> 
> diff --git a/criu/cr-restore.c b/criu/cr-restore.c
> index c248d3df4d07..25e6a106f443 100644
> --- a/criu/cr-restore.c
> +++ b/criu/cr-restore.c
> @@ -2098,6 +2098,43 @@ err:
>  	return ret;
>  }
>  
> +static long restorer_get_mmap_min_addr(void)
> +{
> +	/* CONFIG_LSM_MMAP_MIN_ADDR=65536 */
> +	static const long default_mmap_min_addr = PAGE_SIZE * 0x10;
> +	static const char path[] = "/proc/sys/vm/mmap_min_addr";
> +	static long mmap_min_addr = 0;
> +	char buf[128];
> +	int ret, fd;
> +
> +	if (mmap_min_addr)
> +		return mmap_min_addr;
> +
> +	fd = open(path, O_RDONLY);

Please, use sysctl_op engine for sys-controls.

> +	if (fd < 0) {
> +		pr_perror("Can't open %s, switching to default", path);
> +		return default_mmap_min_addr;
> +	}
> +
> +	ret = read(fd, buf, sizeof(buf));
> +	/* Al least it should be 4096, or something */
> +	if (ret < 4) {
> +		pr_perror("Can't read %s, switching to default", path);
> +		close(fd);
> +		return default_mmap_min_addr;
> +	}
> +	close(fd);
> +
> +	mmap_min_addr = atol(buf);
> +	pr_debug("Obtained %#lx as mmap_min_addr\n", mmap_min_addr);
> +	if (mmap_min_addr < default_mmap_min_addr) {
> +		pr_debug("Adjust %#lx -> %#lx\n", mmap_min_addr, default_mmap_min_addr);
> +		mmap_min_addr = default_mmap_min_addr;
> +	}
> +
> +	return mmap_min_addr;
> +}
> +
>  static long restorer_get_vma_hint(struct list_head *tgt_vma_list,
>  		struct list_head *self_vma_list, long vma_len)
>  {
> @@ -2108,7 +2145,7 @@ static long restorer_get_vma_hint(struct list_head *tgt_vma_list,
>  
>  	end_vma.e = &end_e;
>  	end_e.start = end_e.end = kdat.task_size;
> -	prev_vma_end = PAGE_SIZE * 0x10; /* CONFIG_LSM_MMAP_MIN_ADDR=65536 */
> +	prev_vma_end = restorer_get_mmap_min_addr();
>  
>  	s_vma = list_first_entry(self_vma_list, struct vma_area, list);
>  	t_vma = list_first_entry(tgt_vma_list, struct vma_area, list);
>