Re: [PATCH 04/10] tools/xenstored: Limit the number of requests a connection can delay

[Luca Fancellu <luca.fancellu@xxxxxxx>]

> On 16 Jun 2021, at 15:43, Julien Grall <julien@xxxxxxx> wrote:
> 
> From: Julien Grall <jgrall@xxxxxxxxxx>
> 
> Currently, only liveupdate request can be delayed. The request can only
> be performed by a privileged connection (e.g. dom0). So it is fine to
> have no limits.
> 
> In a follow-up patch we will want to delay request for unprivileged
> connection as well. So it is best to apply a limit.
> 
> For now and for simplicity, only a single request can be delayed
> for a given unprivileged connection.
> 
> Take the opportunity to tweak the prototype and provide a way to
> bypass the quota check. This would be useful when the function
> is called from the restore code.
> 
> Signed-off-by: Julien Grall <jgrall@xxxxxxxxxx>

Reviewed-by: Luca Fancellu <luca.fancellu@xxxxxxx>

> ---
> tools/xenstore/xenstored_control.c |  2 +-
> tools/xenstore/xenstored_core.c    | 11 ++++++++++-
> tools/xenstore/xenstored_core.h    |  3 ++-
> 3 files changed, 13 insertions(+), 3 deletions(-)
> 
> diff --git a/tools/xenstore/xenstored_control.c 
> b/tools/xenstore/xenstored_control.c
> index 7acc2d134f9f..1c24d4869eab 100644
> --- a/tools/xenstore/xenstored_control.c
> +++ b/tools/xenstore/xenstored_control.c
> @@ -737,7 +737,7 @@ static const char *lu_start(const void *ctx, struct 
> connection *conn,
>       lu_status->timeout = to;
>       lu_status->started_at = time(NULL);
> 
> -     errno = delay_request(conn, conn->in, do_lu_start, NULL);
> +     errno = delay_request(conn, conn->in, do_lu_start, NULL, false);
> 
>       return NULL;
> }
> diff --git a/tools/xenstore/xenstored_core.c b/tools/xenstore/xenstored_core.c
> index 41b26d7094c8..51d210828922 100644
> --- a/tools/xenstore/xenstored_core.c
> +++ b/tools/xenstore/xenstored_core.c
> @@ -279,10 +279,19 @@ static void call_delayed(struct connection *conn, 
> struct delayed_request *req)
> }
> 
> int delay_request(struct connection *conn, struct buffered_data *in,
> -               bool (*func)(struct delayed_request *), void *data)
> +               bool (*func)(struct delayed_request *), void *data,
> +               bool no_quota_check)
> {
>       struct delayed_request *req;
> 
> +     /*
> +      * Only allow one request can be delayed for an unprivileged
> +      * connection.
> +      */
> +     if (!no_quota_check && domain_is_unprivileged(conn) &&
> +         !list_empty(&conn->delayed))
> +             return ENOSPC;
> +
>       req = talloc(in, struct delayed_request);
>       if (!req)
>               return ENOMEM;
> diff --git a/tools/xenstore/xenstored_core.h b/tools/xenstore/xenstored_core.h
> index 89ce155e755b..34839b34f6e9 100644
> --- a/tools/xenstore/xenstored_core.h
> +++ b/tools/xenstore/xenstored_core.h
> @@ -213,7 +213,8 @@ char *get_parent(const void *ctx, const char *node);
> 
> /* Delay a request. */
> int delay_request(struct connection *conn, struct buffered_data *in,
> -               bool (*func)(struct delayed_request *), void *data);
> +               bool (*func)(struct delayed_request *), void *data,
> +               bool no_quota_check);
> 
> /* Tracing infrastructure. */
> void trace_create(const void *data, const char *type);
> -- 
> 2.17.1
> 
>