[Xen-devel] [PATCH 07/22] Add support for transitive grants.

[<steven.smith@xxxxxxxxxx>]

These allow a domain A which has been granted access on a page of
domain B's memory to issue domain C with a copy-grant on the same
page.  This is useful e.g. for forwarding packets between domains.

Signed-off-by: Steven Smith <steven.smith@xxxxxxxxxx>
---
 drivers/xen/core/gnttab.c |   32 ++++++++++++++++++++++++++++++++
 include/xen/gnttab.h      |    8 ++++++++
 2 files changed, 40 insertions(+), 0 deletions(-)

diff --git a/drivers/xen/core/gnttab.c b/drivers/xen/core/gnttab.c
index b32dd5d..02790fe 100644
--- a/drivers/xen/core/gnttab.c
+++ b/drivers/xen/core/gnttab.c
@@ -237,6 +237,38 @@ int gnttab_subpage_grants_available(void)
 }
 EXPORT_SYMBOL_GPL(gnttab_subpage_grants_available);
 
+int gnttab_grant_foreign_access_trans(domid_t domid, int flags,
+                                    domid_t trans_domid,
+                                    grant_ref_t trans_gref)
+{
+       int ref;
+
+       if (unlikely((ref = get_free_entry()) < 0))
+               return -ENOSPC;
+
+       gnttab_grant_foreign_access_ref_trans(ref, domid, flags,
+                                             trans_domid, trans_gref);
+
+       return ref;
+}
+EXPORT_SYMBOL_GPL(gnttab_grant_foreign_access_trans);
+
+void gnttab_grant_foreign_access_ref_trans(grant_ref_t ref, domid_t domid,
+                                         int flags,
+                                         domid_t trans_domid,
+                                         grant_ref_t trans_gref)
+{
+       BUG_ON(flags & (GTF_accept_transfer | GTF_reading |
+                      GTF_writing | GTF_sub_page | GTF_permit_access));
+       BUG_ON(grant_table_version == 1);
+       shared.v2[ref].transitive.trans_domid = trans_domid;
+       shared.v2[ref].transitive.gref = trans_gref;
+       shared.v2[ref].hdr.domid = domid;
+       wmb();
+       shared.v2[ref].hdr.flags = GTF_permit_access | GTF_transitive | flags;
+}
+EXPORT_SYMBOL_GPL(gnttab_grant_foreign_access_ref_trans);
+
 int gnttab_query_foreign_access(grant_ref_t ref)
 {
        u16 nflags;
diff --git a/include/xen/gnttab.h b/include/xen/gnttab.h
index 90201da..30be437 100644
--- a/include/xen/gnttab.h
+++ b/include/xen/gnttab.h
@@ -58,6 +58,10 @@ int gnttab_grant_foreign_access_subpage(domid_t domid, 
unsigned long frame,
                                        int flags, unsigned page_off,
                                        unsigned length);
 
+void gnttab_grant_foreign_access_ref_trans(grant_ref_t ref, domid_t domid,
+                                          int flags,
+                                          domid_t trans_domid,
+                                          grant_ref_t trans_gref);
 
 /*
  * Are sub-page grants available on this version of Xen?  Returns 1 if
@@ -114,6 +118,10 @@ void gnttab_grant_foreign_access_ref_subpage(grant_ref_t 
ref, domid_t domid,
                                             unsigned long frame, int flags,
                                             unsigned page_off,
                                             unsigned length);
+void gnttab_grant_foreign_access_ref_trans(grant_ref_t ref, domid_t domid,
+                                          int flags,
+                                          domid_t trans_domid,
+                                          grant_ref_t trans_gref);
 
 void gnttab_grant_foreign_transfer_ref(grant_ref_t, domid_t domid,
                                       unsigned long pfn);
-- 
1.6.3.1


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