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 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).

> 
> As such lets clarify what '->err' and '->result' are
> suppose to contain.
> 
> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
> ---
>  xen/include/public/io/pciif.h | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/xen/include/public/io/pciif.h b/xen/include/public/io/pciif.h
> index a4ba13c..535963a 100644
> --- a/xen/include/public/io/pciif.h
> +++ b/xen/include/public/io/pciif.h
> @@ -71,7 +71,7 @@ struct xen_pci_op {
>      /* IN: what action to perform: XEN_PCI_OP_* */
>      uint32_t cmd;
>  
> -    /* OUT: will contain an error number (if any) from errno.h */
> +    /* OUT: will contain an XEN_PCI_ERR_* value. */
>      int32_t err;
>  
>      /* IN: which device to touch */
> @@ -83,7 +83,9 @@ struct xen_pci_op {
>      int32_t offset;
>      int32_t size;
>  
> -    /* IN/OUT: Contains the result after a READ or the value to WRITE */
> +    /* IN/OUT: Contains the result after a READ or the value to WRITE.
> +     * If the err does not have XEN_PCI_ERR_success, depending on

s/the err does not have/err is not/

> +     *  XEN_PCI_OP_* might have the errno value. */

might under what circumstances? Can that be documented (perhaps as a
default here and a small number of exceptions?)

>      uint32_t value;
>      /* IN: Contains extra infor for this operation */
>      uint32_t info;