[Spice-devel] [PATCH V2] usbredir: fix redirection of user-accesible device nodes.

[Christophe Fergeau]

On Fri, Jul 10, 2015 at 01:33:41PM +0200, Michal Suchanek wrote:
> Excerpts from Christophe Fergeau's message of Fri Jul 10 10:23:33 +0200 2015:
> > On Fri, Jul 10, 2015 at 10:18:15AM +0200, Michal Suchanek wrote:
> > > Excerpts from Christophe Fergeau's message of Thu Jul 09 17:11:45 +0200 2015:
> > > > On Thu, Jul 09, 2015 at 04:58:52PM +0200, Michal Suchanek wrote:
> > > > > Excerpts from Christophe Fergeau's message of Thu Jul 09 16:41:58 +0200 2015:
> > > > > > > -    spice_usb_acl_helper_open_acl_finish(acl_helper, acl_res, &err);
> > > > > > > -    if (!err && priv->state == STATE_DISCONNECTING) {
> > > > > > > +    spice_usb_acl_helper_open_acl_finish(acl_helper, acl_res, &acl_err);
> > > > > > > +    if (!acl_err && priv->state == STATE_DISCONNECTING) {
> > > > > > 
> > > > > > Here I'm wondering if you should not drop the if (!acl_err) part.
> > > > > 
> > > > > That's the original code. It's probably meant to show the cancelling
> > > > > error only if no other error happened so far.
> > > > > 
> > > > > Either way if acl_err is set it will be shown regardless of err.
> > > > 
> > > > The initial code reads "if state is DISCONNECTING, then set 'err' if
> > > > it's not set already" that is, "if _open_acl_finish() returned an error,
> > > > or if state is DISCONNECTING, then 'err' is set, and we will report an
> > > > error"
> > > > After your changes, this has become "if _open_acl_finish() did not return an
> > > > error and state is DISCONNECTING, then 'err' is set, annd we will
> > > > rerport an error". In particular, in the case when '_open_acl_finish() returned an
> > > > error, and open_device() succeeded, no error will be returned'. In my
> > > > opinion, it makes more sense as "if state is _DISCONNECTING regardless
> > > > of acl_error, then return an error".
> > > > 
> > > > (let me know if I'm not making myself clear)
> > > > 
> > > > Christophe
> > > 
> > > And that's discussed in the latter part of the previous email you
> > > trimmed. I missed this case when err is set by hand and removed the
> > > if (err) part which skips the cancellation check.
> > 
> > No I think this is something different, think about acl_err being set,
> > priv->state == STATE_DISCONNECTING, and _open_device() succeeding (so
> > err is not set).
> > 
> Which is fixed by retaining the if (err) check around _open_device().

I don't think so. If _open_acl_finish() fails and priv->state is
DISCONNECTING, and _open_device() succeeds:

Before:
    spice_usb_acl_helper_open_acl_finish(acl_helper, acl_res, &err);
    if (!err && priv->state == STATE_DISCONNECTING) {
        err = g_error_new_literal(G_IO_ERROR, G_IO_ERROR_CANCELLED,
                                  "USB redirection channel connect cancelled");
    }
    if (!err) {
        spice_usbredir_channel_open_device(channel, &err);
    }
    if (err) {
        /* report error */
    }

Here 'err' will be set after the _open_acl_finish() call, priv->state will not
be checked (even though priv->state is DISCONNECTING), but _open_device() will
not be attempted and an error will be reported.

After:
    spice_usb_acl_helper_open_acl_finish(acl_helper, acl_res, &acl_err);
    if (!acl_err && priv->state == STATE_DISCONNECTING) {
        err = g_error_new_literal(G_IO_ERROR, G_IO_ERROR_CANCELLED,
                                  "USB redirection channel connect cancelled");
    }

    if (!err) {
        spice_usbredir_channel_open_device(channel, &err);
    }
    if (err) {
        /* report error */
    }

acl_err will be non-NULL so priv->state will not be checked, open_device
succeeds, no error reported.


Maybe we can't get STATE_DISCONNECTING in the situation I describe, maybe we
can get it, but this is not important, but I thought I'd ask :)

Christophe
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