Re: [PATCH 04/29] tools/xenlogd: add transport layer

[Juergen Gross <jgross@xxxxxxxx>]

On 02.11.23 19:30, Jason Andryuk wrote:
> On Wed, Nov 1, 2023 at 5:34 AM Juergen Gross <jgross@xxxxxxxx> wrote:
> > Add the transport layer of 9pfs. This is basically the infrastructure
> > to receive requests from the frontend and to send the related answers
> > via the rings.
> >
> > In order to avoid unaligned accesses e.g. on Arm, add the definition of
> > __packed to the common-macros.h header.
> >
> > Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
> > ---
> > diff --git a/tools/xenlogd/io.c b/tools/xenlogd/io.c
> > index ef0954d69d..590d06e906 100644
> > --- a/tools/xenlogd/io.c
> > +++ b/tools/xenlogd/io.c
> > +static unsigned int get_request_bytes(device *device, unsigned int off,
> > +                                      unsigned int len)
> > +{
> > +    unsigned int size;
> > +    unsigned int out_data = ring_out_data(device);
> > +    RING_IDX prod, cons;
> > +
> > +    size = min(len - off, out_data);
> > +    prod = xen_9pfs_mask(device->intf->out_prod, device->ring_size);
> > +    cons = xen_9pfs_mask(device->cons_pvt_out, device->ring_size);
> > +    xen_9pfs_read_packet(device->buffer + off, device->data.out, size,
> > +                         prod, &cons, device->ring_size);
> > +
> > +    xen_rmb();           /* Read data out before setting visible consumer. */
> > +    device->cons_pvt_out += size;
> > +    device->intf->out_cons = device->cons_pvt_out;
> > +
> > +    /* Signal that more space is available now. */
> > +    xenevtchn_notify(xe, device->evtchn);
> > +
> > +    return size;
> > +}
> > +
> > +static unsigned int put_request_bytes(device *device, unsigned int off,
> > +                                      unsigned int len)
> Should this be named put_response_bytes?
Yes.

> > +{
> > +    unsigned int size;
> > +    unsigned int in_data = ring_in_free(device);
> > +    RING_IDX prod, cons;
> > +
> > +    size = min(len - off, in_data);
> IIUC, len is the total length of the outgoing data.  Maybe total_len
> would be a better name?  I at least read len as just a length for a
> particular call.  Same comment applies to get_request_bytes() if you
> want to follow it.
Fine with me.

> > +    prod = xen_9pfs_mask(device->prod_pvt_in, device->ring_size);
> > +    cons = xen_9pfs_mask(device->intf->in_cons, device->ring_size);
> > +    xen_9pfs_write_packet(device->data.in, device->buffer + off, size,
> > +                          &prod, cons, device->ring_size);
> > +
> > +    xen_wmb();           /* Write data out before setting visible producer. */
> > +    device->prod_pvt_in += size;
> > +    device->intf->in_prod = device->prod_pvt_in;
> > +
> > +    return size;
> > +}
> > +
> >   static bool io_work_pending(device *device)
> >   {
> >       if ( device->stop_thread )
> >           return true;
> > -    return false;
> > +    if ( device->error )
> > +        return false;
> > +    return device->handle_response ? ring_in_free(device)
> > +                                   : ring_out_data(device);
> >   }
> >
> >   void *io_thread(void *arg)
> >   {
> >       device *device = arg;
> > +    unsigned int count = 0;
> > +    struct p9_header hdr;
> > +    bool in_hdr = true;
> > +
> > +    device->max_size = device->ring_size;
> > +    device->buffer = malloc(device->max_size);
> > +    if ( !device->buffer )
> > +    {
> > +        syslog(LOG_CRIT, "memory allocation failure!");
> > +        return NULL;
> > +    }
> >
> >       while ( !device->stop_thread )
> >       {
> > @@ -36,9 +127,56 @@ void *io_thread(void *arg)
> >           }
> >           pthread_mutex_unlock(&device->mutex);
> >
> > -        /* TODO: I/O handling. */
> > +        if ( device->stop_thread || device->error )
> > +            continue;
> > +
> > +        if ( !device->handle_response )
> > +        {
> > +            if ( in_hdr )
> > +            {
> > +                count += get_request_bytes(device, count, sizeof(hdr));
> > +                if ( count != sizeof(hdr) )
> > +                    continue;
> > +                hdr = *(struct p9_header *)device->buffer;
> > +                if ( hdr.size > device->max_size || hdr.size < sizeof(hdr) )
> > +                {
> > +                    syslog(LOG_ERR, "%u.%u specified illegal request length 
> > %u",
> > +                           device->domid, device->devid, hdr.size);
> > +                    device->error = true;
> When device->error is set, io_thread stops processing requests, but do
> we want to also tear down this backend?  The event channel at least is
> left in place and unmasked.
I think tearing down the backend shouldn't be done, but you are right that
the event channel should be kept masked.

> > +                    continue;
> > +                }
> > +                in_hdr = false;
> > +            }
> > +
> > +            count += get_request_bytes(device, count, hdr.size);
> > +            if ( count < hdr.size )
> > +                continue;
> > +
> > +            /* TODO: handle request. */
> > +
> > +            device->handle_response = true;
> > +            hdr.size = ((struct p9_header *)device->buffer)->size;
> hdr.size is set during the struct copy above, so this isn't needed?
It will be needed later when the "TODO" is filled in, as it will then be the
response size.


Juergen

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