Re: [PATCH v2 2/2] vnc: add qmp to support reload vnc tls certificates

[Daniel P . Berrangé]

On Mon, Jan 18, 2021 at 03:27:33PM +0800, Zihao Chang wrote:
> 
> 
> On 2021/1/15 21:47, Daniel P. Berrangé wrote:
> > On Fri, Jan 15, 2021 at 02:37:33PM +0100, Markus Armbruster wrote:
> >> Zihao Chang <changzihao1@huawei.com> writes:
> >>
> >>> QEMU loads vnc tls certificates only when vm is started. This patch
> >>> provides a new qmp to reload vnc tls certificates without restart
> >>> vnc-server/VM.
> >>> {"execute": "reload-vnc-cert"}
> >>>
> >>> Signed-off-by: Zihao Chang <changzihao1@huawei.com>
> >>> ---
> >>>  include/ui/console.h |  1 +
> >>>  monitor/qmp-cmds.c   |  5 +++++
> >>>  qapi/ui.json         | 18 ++++++++++++++++++
> >>>  ui/vnc.c             | 24 ++++++++++++++++++++++++
> >>>  4 files changed, 48 insertions(+)
> >>>
> >>> diff --git a/include/ui/console.h b/include/ui/console.h
> >>> index 5dd21976a3..60a24a8bb5 100644
> >>> --- a/include/ui/console.h
> >>> +++ b/include/ui/console.h
> >>> @@ -441,6 +441,7 @@ int vnc_display_password(const char *id, const char 
> >>> *password);
> >>>  int vnc_display_pw_expire(const char *id, time_t expires);
> >>>  QemuOpts *vnc_parse(const char *str, Error **errp);
> >>>  int vnc_init_func(void *opaque, QemuOpts *opts, Error **errp);
> >>> +void vnc_display_reload_cert(const char *id,  Error **errp);
> >>
> >> Make this return bool, please.
> >>
> I will fix this in the next version.
> Thank your for your reviews.
> 
> >> error.h's big comment:
> >>
> >>  * = Rules =
> >>  *
> >>  * - Functions that use Error to report errors have an Error **errp
> >>  *   parameter.  It should be the last parameter, except for functions
> >>  *   taking variable arguments.
> >>  *
> >>  * - You may pass NULL to not receive the error, &error_abort to abort
> >>  *   on error, &error_fatal to exit(1) on error, or a pointer to a
> >>  *   variable containing NULL to receive the error.
> >>  *
> >>  * - Separation of concerns: the function is responsible for detecting
> >>  *   errors and failing cleanly; handling the error is its caller's
> >>  *   job.  Since the value of @errp is about handling the error, the
> >>  *   function should not examine it.
> >>  *
> >>  * - The function may pass @errp to functions it calls to pass on
> >>  *   their errors to its caller.  If it dereferences @errp to check
> >>  *   for errors, it must use ERRP_GUARD().
> >>  *
> >>  * - On success, the function should not touch *errp.  On failure, it
> >>  *   should set a new error, e.g. with error_setg(errp, ...), or
> >>  *   propagate an existing one, e.g. with error_propagate(errp, ...).
> >>  *
> >>  * - Whenever practical, also return a value that indicates success /
> >>  *   failure.  This can make the error checking more concise, and can
> >>  *   avoid useless error object creation and destruction.  Note that
> >>  *   we still have many functions returning void.  We recommend
> >>  *   • bool-valued functions return true on success / false on failure,
> >>  *   • pointer-valued functions return non-null / null pointer, and
> >>  *   • integer-valued functions return non-negative / negative.
> >>
> >>>  
> >>>  /* input.c */
> >>>  int index_from_key(const char *key, size_t key_length);
> >>> diff --git a/monitor/qmp-cmds.c b/monitor/qmp-cmds.c
> >>> index 34f7e75b7b..84f2b74ea8 100644
> >>> --- a/monitor/qmp-cmds.c
> >>> +++ b/monitor/qmp-cmds.c
> >>> @@ -287,6 +287,11 @@ static void qmp_change_vnc(const char *target, bool 
> >>> has_arg, const char *arg,
> >>>          qmp_change_vnc_listen(target, errp);
> >>>      }
> >>>  }
> >>> +
> >>> +void qmp_reload_vnc_cert(Error **errp)
> >>> +{
> >>> +    vnc_display_reload_cert(NULL, errp);
> >>> +}
> >>>  #endif /* !CONFIG_VNC */
> >>>  
> >>>  void qmp_change(const char *device, const char *target,
> >>> diff --git a/qapi/ui.json b/qapi/ui.json
> >>> index d08d72b439..855b1ac007 100644
> >>> --- a/qapi/ui.json
> >>> +++ b/qapi/ui.json
> >>> @@ -1179,3 +1179,21 @@
> >>>  ##
> >>>  { 'command': 'query-display-options',
> >>>    'returns': 'DisplayOptions' }
> >>> +
> >>> +##
> >>> +# @reload-vnc-cert:
> >>> +#
> >>> +# Reload certificates for vnc.
> >>> +#
> >>> +# Returns: nothing
> >>> +#
> >>> +# Since: 5.2
> >>
> >> 6.0 now.
> >>
> >>> +#
> >>> +# Example:
> >>> +#
> >>> +# -> { "execute": "reload-vnc-cert" }
> >>> +# <- { "return": {} }
> >>> +#
> >>> +##
> >>> +{ 'command': 'reload-vnc-cert',
> >>> +  'if': 'defined(CONFIG_VNC)' }
> >>
> >> Daniel's objection to another patch that adds a rather specialized QMP
> >> command may apply: "I'm not a fan of adding adhoc new commands for
> >> specific properties."
> >>
> >>     From: Daniel P. Berrangé <berrange@redhat.com>
> >>     Subject: Re: [PATCH] vnc: add qmp to support change authz
> >>     Message-ID: <20210107161830.GE1029501@redhat.com>
> > 
> > Yeah, though this scenario is a ittle more complicated. Tihs patch is
> > not actually changing any object properties in the VNC server config.
> > It is simply telling the VNC server to reload the existing object it
> > has configured.
> > 
> > My proposed  "display-update" command would not directly map to what
> > this "reload-vnc-cert" command does, unless we declared the certs are
> > always reloaded after every display-update command.
> > 
> > Or we could have a more generic  "display-reload" command, which has
> > fields indicating what aspect to reload. eg a 'tls-certs: bool' field
> > to indicate reload of TLS certs in the display. This could be useful
> > if we wanted the ability to reload authz access control lists, though
> > we did actually wire them up to auto-reload using inotify.
> > 
> > 
> > Regards,
> > Daniel
> > 
> 
> If we add field for each reloadable attribute(tls-certs, authz,...),
> the number of parameters for qmp_display_reload() may increase sharply
> (bool has_tls_certs, bool tls_certs, ... twice the number of attributes).

There's a fairly limited conceptual set of VNC features which are going
to require a reload operation, so I don't think it'll grow too unreasonably
large.

> How about using a list[] to determine which attributes need to be
> reloaded["tls_certs", "authz*"...], and define an enum to ensure the
> validity of list elements.

The enum is simple, but if we require data to be provided fr the
reload operation, instead of a simple boolean, then it gets a bit
more limiting.


Regards,
Daniel
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