[CRIU] [PATCH 4/5] files: open files on overmounted mounts are not supported

[Andrey Vagin]

On Mon, Sep 17, 2018 at 02:47:56PM +0300, Pavel Tikhomirov wrote:
> Files from such mounts can switch on restore to different files on the
> overmounting mount, as we yet don't fully control the mount on which
> the file is restored.

I don't understand what is going on here with overmounted mounts. Could
you explain with more details.

> 
> Signed-off-by: Pavel Tikhomirov <ptikhomirov at virtuozzo.com>
> ---
>  criu/files-reg.c     | 13 +++++++++----
>  criu/include/mount.h |  1 +
>  criu/mount.c         |  2 +-
>  3 files changed, 11 insertions(+), 5 deletions(-)
> 
> diff --git a/criu/files-reg.c b/criu/files-reg.c
> index e3ed01f55..f7247e488 100644
> --- a/criu/files-reg.c
> +++ b/criu/files-reg.c
> @@ -1288,7 +1288,7 @@ static bool should_check_size(int flags)
>  int dump_one_reg_file(int lfd, u32 id, const struct fd_parms *p)
>  {
>  	struct fd_link _link, *link;
> -	struct ns_id *nsid;
> +	struct mount_info *mi;
>  	struct cr_img *rimg;
>  	char ext_id[64];
>  	FileEntry fe = FILE_ENTRY__INIT;
> @@ -1312,13 +1312,18 @@ int dump_one_reg_file(int lfd, u32 id, const struct fd_parms *p)
>  		goto ext;
>  	}
>  
> -	nsid = lookup_nsid_by_mnt_id(p->mnt_id);
> -	if (nsid == NULL) {
> +	mi = lookup_mnt_id(p->mnt_id);
> +	if (mi == NULL) {
>  		pr_err("Can't lookup mount=%d for fd=%d path=%s\n",
>  			p->mnt_id, p->fd, link->name + 1);
>  		return -1;
>  	}
>  
> +	if (mnt_is_overmounted(mi)) {
> +		pr_err("Open files on overmounted mounts are not supported yet\n");
> +		return -1;
> +	}
> +
>  	if (p->mnt_id >= 0 && (root_ns_mask & CLONE_NEWNS)) {
>  		rfe.mnt_id = p->mnt_id;
>  		rfe.has_mnt_id = true;
> @@ -1335,7 +1340,7 @@ int dump_one_reg_file(int lfd, u32 id, const struct fd_parms *p)
>  		return -1;
>  	}
>  
> -	if (check_path_remap(link, p, lfd, id, nsid))
> +	if (check_path_remap(link, p, lfd, id, mi->nsid))
>  		return -1;
>  	rfe.name	= &link->name[1];
>  ext:
> diff --git a/criu/include/mount.h b/criu/include/mount.h
> index 776c348cd..43cfe788a 100644
> --- a/criu/include/mount.h
> +++ b/criu/include/mount.h
> @@ -129,5 +129,6 @@ extern struct mount_info *parse_mountinfo(pid_t pid, struct ns_id *nsid, bool fo
>  extern int check_mnt_id(void);
>  
>  extern int remount_readonly_mounts(void);
> +extern int mnt_is_overmounted(struct mount_info *mi);
>  
>  #endif /* __CR_MOUNT_H__ */
> diff --git a/criu/mount.c b/criu/mount.c
> index 3c19c280b..c28af0fe2 100644
> --- a/criu/mount.c
> +++ b/criu/mount.c
> @@ -1152,7 +1152,7 @@ static int get_clean_fd(struct mount_info *mi)
>   * root of our mount namespace as it is covered by other mount.
>   * mnt_is_overmounted() checks if mount is not visible.
>   */
> -static int mnt_is_overmounted(struct mount_info *mi)
> +int mnt_is_overmounted(struct mount_info *mi)
>  {
>  	struct mount_info *t, *c, *m = mi;
>  
> -- 
> 2.17.1
>