[CRIU] AUFS Support in CRIU

[Pavel Emelyanov]

On 08/20/2014 10:21 AM, Saied Kazemi wrote:

>     > Thanks again for your feedback.  I hope the answers are clear.  If it's easier or more productive,
>     > I am available on video chat to discuss in greater detail.  My schedule is flexible, so time
>     > difference shouldn't be a problem.
> 
>     OK, I'll keep that in mind :) Your timezone is US Pacific one, right?
> 
> 
> Yes, I am in Mountain View.
> 
> Looking forward to your comments on this patch which I think has addressed everything above.

Yup, I think this patch is perfect. Only one question left:

> @@ -240,6 +244,31 @@ static int vma_get_mapfile(struct vma_area *vma, DIR *mfd,
>  			vma->vm_socket_id = buf.st_ino;
>  		} else if (errno != ENOENT)
>  			return -1;
> +	} else if (opts.aufs) {
> +		/*
> +		 * AUFS support to compensate for the kernel bug
> +		 * exposing branch pathnames in map_files.
> +		 *
> +		 * If the link points inside a branch, replace it
> +		 * with a pathname from the root for later use in
> +		 * dump_filemap().
> +		 */
> +		char p[PATH_MAX];
> +		int n;
> +
> +		p[0] = '.';
> +		n = read_fd_link(vma->vm_file_fd, &p[1], sizeof p - 1);
> +		if (n < 0)
> +			return -1;
> +		n = fixup_aufs_path(&p[1], sizeof p - 1, true);
> +		if (n < 0)
> +			return -1;
> +		if (n > 0) {
> +			vma->aufs_rpath = xmalloc(n + 2);
> +			if (!vma->aufs_rpath)
> +				return -1;
> +			strcpy(vma->aufs_rpath, p);
> +		}
>  	}
>  
>  	return 0;
> @@ -450,12 +479,24 @@ int parse_smaps(pid_t pid, struct vm_area_list *vma_area_list, bool use_map_file
>  			vma_area->st = prev->st;
>  		} else if (vma_area->vm_file_fd >= 0) {
>  			struct stat *st_buf;
> +			char *f;
>  
>  			st_buf = vma_area->st = xmalloc(sizeof(*st_buf));
>  			if (!st_buf)
>  				goto err;
>  
> -			if (fstat(vma_area->vm_file_fd, st_buf) < 0) {
> +			/*
> +			 * For AUFS support, we cannot fstat() a file descriptor that
> +			 * is a symbolic link to a branch.  Instead, we obtain the
> +			 * pathname of the file from the root and use stat().
> +			 */
> +			if (opts.aufs && (f = fixup_aufs_fd_path(vma_area->vm_file_fd))) {
> +				if (stat(f, st_buf) < 0) {
> +					pr_perror("Failed stat on %d's map %lu (%s)",
> +						pid, start, f);
> +					goto err;
> +				}
> +			} else if (fstat(vma_area->vm_file_fd, st_buf) < 0) {
>  				pr_perror("Failed fstat on %d's map %lu", pid, start);
>  				goto err;
>  			}

Why do we need the 2nd call to fixup branch name? Can't we just stat
the vma->aufs_rpath here?

Thanks,
Pavel