[CRIU] [PATCH v5 18/21] unix: Rework ghost name generation

[Andrey Vagin]

On Thu, May 10, 2018 at 05:57:58PM +0300, Cyrill Gorcunov wrote:
> We need unique names of ghost unix sockets so that they won't
> inetrsect with another simultaneously running criu instance,
> since while using containers with own root fs is a preferred
> there is no mandatory requirement to do so, and people are
> free to c/r individual process trees on the host with
> share root.
> 
> For this sake when we create a unix socket to be treated
> as a ghost (ie with furthre delete once connected) we
> need it to be a unique amont others. For this sake we
> use uuid library which fits our needs. In particular
> ghost names are converted into the form of
> 
>  | /criu-e7845e6a-28f8-41bf-adda-e61efe81b3f4

* We can't create all ghost sockets in /, because it can be read-only.
* We have to create a ghost file on the same mountpoint where is
was before dump.

> 
> The rationale of dropping the former path and make
> such transition is that any directory inside the
> path may absence and they recreation and removing
> while we are creating the socket may race with other
> processes.
> 
> We've been talking to Andrew if there a way to keep
> at least part of the former path for potential debugging
> sake but it looks like even so there is no guarantee
> that some of path won't be unconverted (say complete
> path up to the root is dropped so we could try to
> replace slashes with dashes or something but then
> there is a chance two or more deleted sockets are
> pointing to same name and we will have to resolve
> this conflict by hangs again). Thus as to me the
> unified uuid based scheme a way more preferred.
> 
> Signed-off-by: Cyrill Gorcunov <gorcunov at gmail.com>
> ---
>  criu/sk-unix.c | 29 +++++++++--------------------
>  1 file changed, 9 insertions(+), 20 deletions(-)
> 
> diff --git a/criu/sk-unix.c b/criu/sk-unix.c
> index 03aca89eee18..1ee4d6da075a 100644
> --- a/criu/sk-unix.c
> +++ b/criu/sk-unix.c
> @@ -2,6 +2,7 @@
>  #include <linux/netlink.h>
>  #include <linux/rtnetlink.h>
>  #include <libnl3/netlink/msg.h>
> +#include <uuid/uuid.h>
>  #include <unistd.h>
>  #include <netinet/tcp.h>
>  #include <sys/stat.h>
> @@ -1845,35 +1846,23 @@ static int init_unix_sk_info(struct unix_sk_info *ui, UnixSkEntry *ue)
>  	return 0;
>  }
>  
> -#define GHOST_NAME_FMT		"~criu-%u"
> -#define GHOST_NAME_FMT_PREFIX	6 /* num of chars before counter */
> +#define GHOST_NAME_FMT		"/criu-%s"
>  
>  static int ghost_new_name(char *name, size_t namelen,
>  			  char **name_new, size_t *namelen_new)
>  {
> -	char sname[64], *pos, *oldname = name;
> -	static unsigned int unix_name_cnt = 0;
> +	char uuid_str[64], sname[64], *oldname = name;
> +	uuid_t uuid;
>  	size_t k;
>  
>  	pr_debug("\tghost: handling name %s namelen %zu\n", name, namelen);
>  
> -	for (pos = &name[namelen - 1]; pos > name; pos--) {
> -		if (*pos == GHOST_NAME_FMT[0])
> -			break;
> -	}
> -
> -	if (strncmp(pos, GHOST_NAME_FMT, GHOST_NAME_FMT_PREFIX) == 0) {
> -		unsigned int __cnt;
> -
> -		if (sscanf(pos, GHOST_NAME_FMT, &__cnt) == 1) {
> -			pr_debug("\tghost: unix_name_cnt %d detected\n", __cnt);
> -			if (__cnt != unix_name_cnt)
> -				unix_name_cnt += __cnt;
> -		}
> -	}
> -
>  	memzero(sname, sizeof(sname));
> -	k = snprintf(sname, sizeof(sname), GHOST_NAME_FMT, unix_name_cnt++) + 1;
> +	memzero(uuid_str, sizeof(uuid_str));
> +	uuid_generate(uuid);
> +	uuid_unparse_lower(uuid, uuid_str);
> +
> +	k = snprintf(sname, sizeof(sname), GHOST_NAME_FMT, uuid_str) + 1;
>  	if (k > sizeof(sname) || k > UNIX_PATH_MAX) {
>  		pr_err("\tghost: New name for socket is too long\n");
>  		return -1;
> -- 
> 2.14.3
>