Re: [PATCH 08/10] tools/xenstored: Extend restore code to handle multiple input buffer

[Julien Grall <julien@xxxxxxx>]

Hi Juergen,

On 24/06/2021 10:30, Juergen Gross wrote:
> On 16.06.21 16:43, Julien Grall wrote:
> > From: Julien Grall <jgrall@xxxxxxxxxx>
> >
> > Currently, the restore code is considering the stream will contain at
> > most one in-flight request per connection. In a follow-up changes, we
> > will want to transfer multiple in-flight requests.
> >
> > The function read_state_buffered() is now extended to restore multiple
> > in-flight request. Complete requests will be queued as delayed
> > requests, if there a partial request (only the last one can) then it
> > will used as the current in-flight request.
> >
> > Note that we want to bypass the quota check for delayed requests as
> > the new Xenstore may have a lower limit.
> >
> > Lastly, there is no need to change the specification as there was
> > no restriction on the number of in-flight requests preserved.
> >
> > Signed-off-by: Julien Grall <jgrall@xxxxxxxxxx>
> > ---
> >   tools/xenstore/xenstored_core.c | 56 ++++++++++++++++++++++++++++-----
> >   1 file changed, 48 insertions(+), 8 deletions(-)
> >
> > diff --git a/tools/xenstore/xenstored_core.c 
> > b/tools/xenstore/xenstored_core.c
> > index a5084a5b173d..5b7ab7f74013 100644
> > --- a/tools/xenstore/xenstored_core.c
> > +++ b/tools/xenstore/xenstored_core.c
> > @@ -1486,6 +1486,10 @@ static void process_message(struct connection 
> > *conn, struct buffered_data *in)
> >       enum xsd_sockmsg_type type = in->hdr.msg.type;
> >       int ret;
> > +    /* At least send_error() and send_reply() expects conn->in == in */
> > +    assert(conn->in == in);
> > +    trace_io(conn, in, 0);
> > +
> >       if ((unsigned int)type >= XS_TYPE_COUNT || !wire_funcs[type].func) 
> {
> >           eprintf("Client unknown operation %i", type);
> >           send_error(conn, ENOSYS);
> > @@ -1515,6 +1519,23 @@ static void process_message(struct connection 
> > *conn, struct buffered_data *in)
> >       conn->transaction = NULL;
> >   }
> > +static bool process_delayed_message(struct delayed_request *req)
> > +{
> > +    struct connection *conn = req->data;
> > +    struct buffered_data *saved_in = conn->in;
> > +
> > +    /*
> > +     * Part of process_message() expects conn->in to contains the
> > +     * processed response. So save the current conn->in and restore it
> > +     * afterwards.
> > +     */
> > +    conn->in = req->in;
> > +    process_message(req->data, req->in);
> > +    conn->in = saved_in;
> This pattern was added to do_lu_start() already, and it will be needed
> for each other function being called via call_delayed().
>
> Maybe it would be better to add conn explicitly to struct
> delayed_request (or even better: replace data with conn) and to do the
> conn->in saving/setting/restoring in call_delayed() instead?
This was my original approach, but I abandoned it because in the case of 
do_lu_start() we need to save the original conn->in in the stream (see 
patch #3 for more details).
If we overwrite conn->in in call_delayed(), then we need a different way 
to find the original conn->in. I couldn't find a nice way and decided to 
settle with the duplication.
Cheers,

--
Julien Grall