[Xen-devel] [PATCH] x86/domctl: Improve XEN_DOMCTL_hypercall_init error handling

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

EACCES cannot be distinguished against an incorrect DOMCTL_INTERFACE_VERSION,
and will cause an incorrect "need to rebuild the user-space tool set?" message
from libxc.  EINVAL is a perfectly reasonable alternative.

On the libxc side, put the useful piece of information in the error message,
rathe than the -1 from do_domctl().

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CC: Jan Beulich <JBeulich@xxxxxxxx>
CC: Ian Campbell <Ian.Campbell@xxxxxxxxxx>
CC: Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>
CC: Wei Liu <wei.liu2@xxxxxxxxxx>
---
 tools/libxc/xc_dom_boot.c |    6 +++---
 xen/arch/x86/domctl.c     |    4 +---
 2 files changed, 4 insertions(+), 6 deletions(-)

diff --git a/tools/libxc/xc_dom_boot.c b/tools/libxc/xc_dom_boot.c
index a141eb5..f82db2d 100644
--- a/tools/libxc/xc_dom_boot.c
+++ b/tools/libxc/xc_dom_boot.c
@@ -57,9 +57,9 @@ static int setup_hypercall_page(struct xc_dom_image *dom)
     domctl.u.hypercall_init.gmfn = xc_dom_p2m_guest(dom, pfn);
     rc = do_domctl(dom->xch, &domctl);
     if ( rc != 0 )
-        xc_dom_panic(dom->xch,
-                     XC_INTERNAL_ERROR, "%s: HYPERCALL_INIT failed (rc=%d)",
-                     __FUNCTION__, rc);
+        xc_dom_panic(dom->xch, XC_INTERNAL_ERROR,
+                     "%s: HYPERCALL_INIT failed: %d - %s)",
+                     __FUNCTION__, errno, strerror(errno));
     return rc;
 }
 
diff --git a/xen/arch/x86/domctl.c b/xen/arch/x86/domctl.c
index 3e5bef1..3ffb083 100644
--- a/xen/arch/x86/domctl.c
+++ b/xen/arch/x86/domctl.c
@@ -386,16 +386,14 @@ long arch_do_domctl(
 
         page = get_page_from_gfn(d, gmfn, NULL, P2M_ALLOC);
 
-        ret = -EACCES;
         if ( !page || !get_page_type(page, PGT_writable_page) )
         {
+            ret = -EINVAL;
             if ( page )
                 put_page(page);
             break;
         }
 
-        ret = 0;
-
         hypercall_page = __map_domain_page(page);
         hypercall_page_initialise(d, hypercall_page);
         unmap_domain_page(hypercall_page);
-- 
1.7.10.4


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