Re: [Xen-devel] [PATCH RFC 4/6] xen: Print and use errno where applicable.

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Mon, 29 Jun 2015, Konrad Rzeszutek Wilk wrote:
> In Xen 4.6 commit cd2f100f0f61b3f333d52d1737dd73f02daee592
> "libxc: Fix do_memory_op to return negative value on errors"
> made the libxc API less odd-ball: On errors, return value is
> -1 and error code is in errno. On success the return value
> is either 0 or an positive value.
> 
> Since we could be running with an old toolstack in which the
> Exx value is in rc or the newer, we print both and return
> the -EXX depending on rc == -1 condition.
> 
> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> ---
>  xen-hvm.c | 10 ++++++----
>  1 file changed, 6 insertions(+), 4 deletions(-)
> 
> diff --git a/xen-hvm.c b/xen-hvm.c
> index 0408462..a92bc14 100644
> --- a/xen-hvm.c
> +++ b/xen-hvm.c
> @@ -345,11 +345,12 @@ go_physmap:
>          unsigned long idx = pfn + i;
>          xen_pfn_t gpfn = start_gpfn + i;
>  
> +        /* In Xen 4.6 rc is -1 and errno contains the error value. */
>          rc = xc_domain_add_to_physmap(xen_xc, xen_domid, XENMAPSPACE_gmfn, 
> idx, gpfn);
>          if (rc) {
>              DPRINTF("add_to_physmap MFN %"PRI_xen_pfn" to PFN %"
> -                    PRI_xen_pfn" failed: %d\n", idx, gpfn, rc);
> -            return -rc;
> +                    PRI_xen_pfn" failed: %d (errno: %d)\n", idx, gpfn, rc, 
> errno);
> +            return rc == -1 ? -errno : -rc;

Printing both rc and errno is the right thing to do, but I am not sure
changing return value depending on the libxc version is a good idea.
Maybe we should be consistent and always return rc?


>          }
>      }
>  
> @@ -422,11 +423,12 @@ static int xen_remove_from_physmap(XenIOState *state,
>          xen_pfn_t idx = start_addr + i;
>          xen_pfn_t gpfn = phys_offset + i;
>  
> +        /* In Xen 4.6 rc is -1 and errno contains the error value. */
>          rc = xc_domain_add_to_physmap(xen_xc, xen_domid, XENMAPSPACE_gmfn, 
> idx, gpfn);
>          if (rc) {
>              fprintf(stderr, "add_to_physmap MFN %"PRI_xen_pfn" to PFN %"
> -                    PRI_xen_pfn" failed: %d\n", idx, gpfn, rc);
> -            return -rc;
> +                    PRI_xen_pfn" failed: %d (errno: %d)\n", idx, gpfn, rc, 
> errno);
> +            return rc == -1 ? -errno : -rc;
>          }
>      }
>  
> -- 
> 2.1.0
> 

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