[Xen-devel] [PATCH] xenpaging: unify return value in nominate and evict

[Olaf Hering <olaf@xxxxxxxxx>]

# HG changeset patch
# User Olaf Hering <olaf@xxxxxxxxx>
# Date 1327925194 -3600
# Node ID 17e25c8b6045cd7246e4ee5e914efba6f44a26fd
# Parent  2577131785ab86c95e6631a01bff04c664eac876
xenpaging: unify return value in nominate and evict

Let p2m_mem_paging_nominate and p2m_mem_paging_evict return just one
error number. EINVAL is not very helpful in case of nominate, it can
happen if the pager tries to nominate a ballooned page. In this case the
gfn is not backed by a mfn, the pager can not know that.  Similar with
evict, anything can happen between nominate and evict.

This change helps the pager to decide if the returned error is from the
function itself, or if it happend earlier. In the latter case, it is
most likely fatal and should be handled as such.
nominate and evict return EBUSY, which is supposed to mean
"pager request reached target function, and failed."

Signed-off-by: Olaf Hering <olaf@xxxxxxxxx>

diff -r 2577131785ab -r 17e25c8b6045 xen/arch/x86/mm/p2m.c
--- a/xen/arch/x86/mm/p2m.c
+++ b/xen/arch/x86/mm/p2m.c
@@ -735,19 +735,17 @@ int p2m_mem_paging_nominate(struct domai
     p2m_type_t p2mt;
     p2m_access_t a;
     mfn_t mfn;
-    int ret;
+    int ret = -EBUSY;
 
     p2m_lock(p2m);
 
     mfn = p2m->get_entry(p2m, gfn, &p2mt, &a, p2m_query, NULL);
 
     /* Check if mfn is valid */
-    ret = -EINVAL;
     if ( !mfn_valid(mfn) )
         goto out;
 
     /* Check p2m type */
-    ret = -EAGAIN;
     if ( !p2m_is_pageable(p2mt) )
         goto out;
 
@@ -799,7 +797,7 @@ int p2m_mem_paging_evict(struct domain *
     p2m_access_t a;
     mfn_t mfn;
     struct p2m_domain *p2m = p2m_get_hostp2m(d);
-    int ret = -EINVAL;
+    int ret = -EBUSY;
 
     p2m_lock(p2m);
 
@@ -812,7 +810,6 @@ int p2m_mem_paging_evict(struct domain *
     if ( p2mt != p2m_ram_paging_out )
         goto out;
 
-    ret = -EBUSY;
     /* Get the page so it doesn't get modified under Xen's feet */
     page = mfn_to_page(mfn);
     if ( unlikely(!get_page(page, d)) )

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