Re: [PATCH v2 07/19] tools/xenstore: introduce dummy nodes for special watch paths

[Julien Grall <julien@xxxxxxx>]

Hi Juergen,

On 13/12/2022 16:00, Juergen Gross wrote:
> Instead of special casing the permission handling and watch event
> firing for the special watch paths "@introduceDomain" and
> "@releaseDomain", use static dummy nodes added to the data base when
> starting Xenstore.
>
> The node accounting needs to reflect that change by adding the special
> nodes in the domain_entry_fix() call in setup_structure().
>
> Note that this requires to rework the calls of fire_watches() for the
> special events in order to avoid leaking memory.
>
> Move the check for a valid node name from get_node() to
> get_node_canonicalized(), as it allows to use get_node() for the
> special nodes, too.
>
> In order to avoid read and write accesses to the special nodes use a
> special variant for obtaining the current node data for the permission
> handling.
>
> This allows to simplify quite some code. In future sub-nodes of the
> special nodes will be possible due to this change, allowing more fine
> grained permission control of special events for specific domains.
>
> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
> ---
> V2:
> - add get_spec_node()
> - expand commit message (Julien Grall)
> ---
>   tools/xenstore/xenstored_control.c |   3 -
>   tools/xenstore/xenstored_core.c    |  92 +++++++++-------
>   tools/xenstore/xenstored_domain.c  | 162 ++++-------------------------
>   tools/xenstore/xenstored_domain.h  |   6 --
>   tools/xenstore/xenstored_watch.c   |  17 +--
>   5 files changed, 80 insertions(+), 200 deletions(-)
>
> diff --git a/tools/xenstore/xenstored_control.c 
> b/tools/xenstore/xenstored_control.c
> index d1aaa00bf4..41e6992591 100644
> --- a/tools/xenstore/xenstored_control.c
> +++ b/tools/xenstore/xenstored_control.c
> @@ -676,9 +676,6 @@ static const char *lu_dump_state(const void *ctx, struct 
> connection *conn)
>         if (ret)
>                 goto out;
>         ret = dump_state_connections(fp);
> -       if (ret)
> -               goto out;
> -       ret = dump_state_special_nodes(fp);
>         if (ret)
>                 goto out;
>         ret = dump_state_nodes(fp, ctx);
> diff --git a/tools/xenstore/xenstored_core.c b/tools/xenstore/xenstored_core.c
> index 1650821922..f96714e1b8 100644
> --- a/tools/xenstore/xenstored_core.c
> +++ b/tools/xenstore/xenstored_core.c
> @@ -616,7 +616,8 @@ static void get_acc_data(TDB_DATA *key, struct 
> node_account_data *acc)
>   static unsigned int get_acc_domid(struct connection *conn, TDB_DATA *key,
>                                   unsigned int domid)
>   {
> -       return (!conn || key->dptr[0] == '/') ? domid : conn->id;
> +       return (!conn || key->dptr[0] == '/' || key->dptr[0] == '@')
The comment on top of get_acc_domid() needs to be updated.

> +              ? domid : conn->id;
>   }
>   
[...]

> +static void fire_special_watches(const char *name)
> +{
> +       void *ctx = talloc_new(NULL);
> +       struct node *node;
> +
> +       if (!ctx)
> +               return;
> +
> +       node = read_node(NULL, ctx, name);
> +
> +       if (node)
> +               fire_watches(NULL, ctx, name, node, true, NULL);
NIT: I would consider to log an error (maybe only once) if 'node' is 
NULL. The purpose is to help debugging Xenstored.
The rest of the code LGTM.

Cheers,

--
Julien Grall