[PATCH v9 05/11] xen: grant_table: implement grant_table_warn_active_grants()

[Vitaly Kuznetsov <vkuznets@redhat.com>]

Log first 10 active grants for a domain. This function is going to be used
for soft reset, active grants on this path usually mean misbehaving backends
refusing to release their mappings on shutdown. We need that in addition to
the already existent 'g' keyhandler as such misbehaving backends can cause a
domain to crash right after the soft reset operation and 'g' option won't be
available in this case.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
---
Changes since v8:
- Use WARN_GRANT_MAX define instead of hardcoded 10 [Konrad Rzeszutek Wilk]
- Update commit message explaining why 'g' keyhandler is not enough
  [Konrad Rzeszutek Wilk]
---
 xen/common/grant_table.c      | 35 +++++++++++++++++++++++++++++++++++
 xen/include/xen/grant_table.h |  5 +++++
 2 files changed, 40 insertions(+)

diff --git a/xen/common/grant_table.c b/xen/common/grant_table.c
index 92f078e..c2e0210 100644
--- a/xen/common/grant_table.c
+++ b/xen/common/grant_table.c
@@ -3348,6 +3348,41 @@ gnttab_release_mappings(
     }
 }
 
+void grant_table_warn_active_grants(struct domain *d)
+{
+    struct grant_table *gt = d->grant_table;
+    struct active_grant_entry *act;
+    grant_ref_t ref;
+    unsigned int nr_active = 0;
+
+#define WARN_GRANT_MAX 10
+
+    read_lock(&gt->lock);
+
+    for ( ref = 0; ref != nr_grant_entries(gt); ref++ )
+    {
+        act = active_entry_acquire(gt, ref);
+        if ( !act->pin )
+        {
+            active_entry_release(act);
+            continue;
+        }
+
+        nr_active++;
+        if ( nr_active <= WARN_GRANT_MAX )
+            printk(XENLOG_G_DEBUG "Dom%d has an active grant: GFN: %lx"
+                   " (MFN: %lx)\n", d->domain_id, act->gfn, act->frame);
+        active_entry_release(act);
+    }
+
+    if ( nr_active > WARN_GRANT_MAX )
+        printk(XENLOG_G_DEBUG "Dom%d has too many (%d) active grants"
+               " to report\n", d->domain_id, nr_active);
+
+    read_unlock(&gt->lock);
+
+#undef WARN_GRANT_MAX
+}
 
 void
 grant_table_destroy(
diff --git a/xen/include/xen/grant_table.h b/xen/include/xen/grant_table.h
index 9c7b5a3..54005cc 100644
--- a/xen/include/xen/grant_table.h
+++ b/xen/include/xen/grant_table.h
@@ -90,6 +90,11 @@ void grant_table_destroy(
     struct domain *d);
 void grant_table_init_vcpu(struct vcpu *v);
 
+/*
+ * Check if domain has active grants and log first 10 of them.
+ */
+void grant_table_warn_active_grants(struct domain *d);
+
 /* Domain death release of granted mappings of other domains' memory. */
 void
 gnttab_release_mappings(
-- 
2.4.3