Re: [PATCH] xen/pciif: Clarify what values go in op->err and op->result.

[Ian Campbell <ian.campbell@citrix.com>]

On Tue, 2015-03-31 at 12:29 -0400, Konrad Rzeszutek Wilk wrote:
> On Tue, Mar 31, 2015 at 05:05:23PM +0100, Ian Campbell wrote:
> > On Tue, 2015-03-31 at 10:58 -0400, Konrad Rzeszutek Wilk wrote:
> > > The earlier comment says that errno values go in op->err.
> > > However all implementations (NetBSD, Linux) of the most
> > > common operations use XEN_PCI_ERR_* instead of -EXX values.
> > > 
> > > The exception is the xen-pciback in Linux code when doing
> > > XEN_PCI_OP_enable_msix can stash the -EXX in op->result
> > > and in op->err.
> > 
> > i.e. both of them contain the same thing? How unhelpful!
> > 
> > What would be the impact of "correcting" ->result to do the right thing?
> > (as documented below after this patch).
> 
> Ugh. The frontend (Linux) first checks op->err. If it is non-zero
> then it returns op->err back up. If op->err is zero
> but op->result is non-zero, then it returns op->result up the
> stack.
> 
> The 'stack' differs depending on what XEN_PCI_OP it is.
> 
> For XEN_PCI_OP_conf_read and XEN_PCI_OP_conf_write
> it expects 'err' to contain XEN_PCI_ERR* values. And it converts them.
> 
> In upstream Linux:
> The XEN_PCI_OP_enable_msix it expects 'err' to contain
> -EXX values.  Which means that whoever called 'pci_enable_msi_range' will
> get the 'err' value.
> 
> In Linux 2.6.18, if 'err' has any value it will convert all of them
> to '-EINVAL'.
> 
> For XEN_PCI_OP_enable_msi if 'err' has any value it will convert
> all of them to -EINVAL.
> 
> For XEN_PCI_OP_disable_msix and XEN_PCI_OP_disable_msi it just
> reports the value.
> 
> NetBSD only implements XEN_PCI_OP_conf_write and XEN_PCI_OP_conf_read.
> 
> It looks to me that the upstream Linux kernel frontend driver needs
> to do what the linux-2.6.18 does (return -EINVAL if there are any errors).

So what are the next steps? Patches to other things? What about this
one, should I expect a new version, drop it or apply it?