[CRIU] Re: [PATCH cr 07/16] restore: map private vma-s before forking children

[Pavel Emelyanov]

On 10/23/2012 02:02 PM, Andrey Vagin wrote:
> In this case private vma-s will be inherited by children,
> it allows to restore copy-on-write reqions.
> 
> This code compares child and parent vma lists. If it found
> two vma-s with the same start and end addresses, it decides
> that the child inherites this vmas from the parent.
> 
> This code calculates a size of all private vma-s, then allocate
> a memory region for all vma-s and maps them one by one. If a vma is
> inherited it will be remaped to an allocated place.
> 
> As a result all vma-s will be placed in a continious memory region
> and sorted by start addresses. This logic will be used for remap
> vma-s to correct address.
> 
> Signed-off-by: Andrey Vagin <avagin at openvz.org>
> ---
>  cr-restore.c |  104 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++-
>  1 files changed, 103 insertions(+), 1 deletions(-)
> 
> diff --git a/cr-restore.c b/cr-restore.c
> index 9d1fdea..b11fae3 100644
> --- a/cr-restore.c
> +++ b/cr-restore.c
> @@ -173,15 +173,77 @@ err:
>  	return ret;
>  }
>  
> +/* Map a private vma, if it is not mapped by a parrent yet */
> +static int map_private_vma(pid_t pid, struct vma_area *vma, void *tgt_addr,

Unused pid argument.

> +			struct vma_area **pvma, struct list_head *pvma_list)
> +{
> +	void *addr;
> +	struct vma_area *p = *pvma;
> +
> +	list_for_each_entry_continue(p, pvma_list, list) {
> +		if (p->vma.start > vma->vma.start)
> +			 break;
> +
> +		if (p->vma.end == vma->vma.end &&
> +		    p->vma.start == vma->vma.start) {
> +			pr_info("COW 0x%016lx-0x%016lx 0x%016lx vma\n",
> +				vma->vma.start, vma->vma.end, vma->vma.pgoff);
> +			vma->vma.shmid = vma_premmaped_start(&p->vma);

Use helper. Like vma_premmaped_start(vma) = vma_premmaped_start(&p->vma).

> +			break;
> +		}
> +
> +	}
> +
> +	*pvma = list_entry(p->list.prev, struct vma_area, list);

prev? Why prev? We should move forward the parent list. No?

> +
> +	if (!vma_premmaped_start(&vma->vma)) {
> +		pr_info("Map 0x%016lx-0x%016lx 0x%016lx vma\n",
> +			vma->vma.start, vma->vma.end, vma->vma.pgoff);
> +
> +		addr = mmap(tgt_addr, vma_entry_len(&vma->vma),
> +				vma->vma.prot | PROT_WRITE,
> +				vma->vma.flags | MAP_FIXED,
> +				vma->vma.fd, vma->vma.pgoff);
> +
> +		if (addr == MAP_FAILED) {
> +			pr_perror("Unable to map ANON_VMA");
> +			return -1;
> +		}
> +		vma->vma.shmid = (unsigned long) addr;

Helper here as well.

> +	} else {
> +		addr = mremap((void *)vma_premmaped_start(&vma->vma),
> +				vma_area_len(vma), vma_area_len(vma),
> +				MREMAP_FIXED | MREMAP_MAYMOVE, tgt_addr);
> +		if (addr != tgt_addr) {
> +			pr_perror("Unable to remap a private vma");
> +			return -1;
> +		}
> +
> +		vma->vma.shmid = (unsigned long) addr;

And helper here.

> +
> +		list_del(&p->list);
> +		xfree(p);

Why do we remove parent vma from its list?

> +	}
> +
> +	if (vma_entry_is(&vma->vma, VMA_FILE_PRIVATE))
> +		close(vma->vma.fd);

Plz, explain this close.

> +
> +	return 0;
> +}
> +
>  static int read_vmas(int pid)
>  {
>  	int fd, ret = 0;
>  	LIST_HEAD(old);
> -	struct vma_area *vma;
> +	struct vma_area *pvma, *vma;
> +	unsigned long priv_size = 0;
> +	void *addr;
>  
>  	list_replace_init(&vma_list, &old);
>  	INIT_LIST_HEAD(&vma_list);
>  
> +	pvma = list_first_entry(&old, struct vma_area, list);

Plz, move below, closer to the place it's really required.

> +
>  	/* Skip errors, because a zombie doesn't have an image of vmas */
>  	fd = open_image_ro(CR_FD_VMAS, pid);
>  	if (fd < 0)
> @@ -211,14 +273,54 @@ static int read_vmas(int pid)
>  
>  		vma->vma = *e;
>  		vma_entry__free_unpacked(e, NULL);
> +
> +		if (!vma_priv(&vma->vma))
> +			continue;
> +
> +		priv_size += vma_area_len(vma);
> +	}
> +
> +	/* Reserve a place for mapping private vma-s one by one */
> +	addr = mmap(NULL, priv_size, PROT_NONE, MAP_PRIVATE | MAP_ANONYMOUS, 0, 0);
> +	if (addr == MAP_FAILED) {
> +		pr_perror("Unable to reserve memory");
> +		return -1;
> +	}
> +
> +	list_for_each_entry(vma, &vma_list, list) {
> +		if (!vma_priv(&vma->vma))
> +			continue;
> +
> +		ret = map_private_vma(pid, vma, addr, &pvma, &old);
> +		if (ret < 0)
> +			break;
> +
> +		addr += vma_area_len(vma);

Both addr and pvma propagation should be done in one place for better code readability.

>  	}
>  
>  	close(fd);
>  
>  out:
>  	while (!list_empty(&old)) {
> +		unsigned long len;
> +
>  		vma = list_first_entry(&old, struct vma_area, list);
>  		list_del(&vma->list);
> +
> +		if (!vma_priv(&vma->vma))
> +			continue;

continue? How about xfree?

> +
> +		addr = (void *) vma_premmaped_start(&vma->vma);
> +		len = vma_area_len(vma);
> +
> +		if (!addr)
> +			continue;
> +
> +		if (munmap(addr, len)) {

What is this munmap for?

> +			pr_perror("Unable to unmap %p-%p", addr, addr + len);
> +			return -1;
> +		}
> +
>  		xfree(vma);
>  	}
>  
>