[Xen-changelog] Simpler domid allocation.

[Xen patchbot -unstable <patchbot-unstable@xxxxxxxxxxxxxxxxxxx>]

# HG changeset patch
# User kaf24@xxxxxxxxxxxxxxxxxxxx
# Node ID 8d04aa7b42805d6d15c651abe13249c4d2eefaf7
# Parent  1d026c7023d28aad1a409638d4f1db518a80bdfd

Simpler domid allocation.
Signed-off-by: Keir Fraser <keir@xxxxxxxxxxxxx>

diff -r 1d026c7023d2 -r 8d04aa7b4280 xen/common/dom0_ops.c
--- a/xen/common/dom0_ops.c     Thu Jul 14 23:48:06 2005
+++ b/xen/common/dom0_ops.c     Fri Jul 15 07:53:46 2005
@@ -37,55 +37,6 @@
 
     put_domain(d);
     return 0;
-}
-
-/*
- * Allocate a free domain id. We try to reuse domain ids in a fairly low range,
- * only expanding the range when there are no free domain ids. This is to keep 
- * domain ids in a range depending on the number that exist simultaneously,
- * rather than incrementing domain ids in the full 32-bit range.
- */
-static int allocate_domid(domid_t *pdom)
-{
-    static spinlock_t domid_lock = SPIN_LOCK_UNLOCKED;
-    static domid_t curdom = 0;
-    static domid_t topdom = 101;
-    int err = 0;
-    domid_t dom;
-
-    spin_lock(&domid_lock);
-
-    /* Try to use a domain id in the range 0..topdom, starting at curdom. */
-    for ( dom = curdom + 1; dom != curdom; dom++ )
-    {
-        if ( dom == topdom )
-            dom = 1;
-        if ( is_free_domid(dom) )
-            goto exit;
-    }
-
-    /* Couldn't find a free domain id in 0..topdom, try higher. */
-    for ( dom = topdom; dom < DOMID_FIRST_RESERVED; dom++ )
-    {
-        if ( is_free_domid(dom) )
-        {
-            topdom = dom + 1;
-            goto exit;
-        }
-    }
-
-    /* No free domain ids. */
-    err = -ENOMEM;
-
-  exit:
-    if ( err == 0 )
-    {
-        curdom = dom;
-        *pdom = dom;
-    }
-
-    spin_unlock(&domid_lock);
-    return err;
 }
 
 static void getdomaininfo(struct domain *d, dom0_getdomaininfo_t *info)
@@ -217,18 +168,33 @@
         domid_t        dom;
         struct vcpu   *v;
         unsigned int   i, cnt[NR_CPUS] = { 0 };
-
+        static spinlock_t alloc_lock = SPIN_LOCK_UNLOCKED;
+        static domid_t rover = 0;
+
+        spin_lock(&alloc_lock);
 
         dom = op->u.createdomain.domain;
         if ( (dom > 0) && (dom < DOMID_FIRST_RESERVED) )
         {
             ret = -EINVAL;
             if ( !is_free_domid(dom) )
-                break;
-        }
-        else if ( (ret = allocate_domid(&dom)) != 0 )
-        {
-            break;
+                goto alloc_out;
+        }
+        else
+        {
+            for ( dom = rover + 1; dom != rover; dom++ )
+            {
+                if ( dom == DOMID_FIRST_RESERVED )
+                    dom = 0;
+                if ( is_free_domid(dom) )
+                    break;
+            }
+
+            ret = -ENOMEM;
+            if ( dom == rover )
+                goto alloc_out;
+
+            rover = dom;
         }
 
         /* Do an initial CPU placement. Pick the least-populated CPU. */
@@ -249,11 +215,12 @@
                 pro = i;
 
         ret = -ENOMEM;
-        if ( (d = do_createdomain(dom, pro)) == NULL )
-            break;
-
-        ret = 0;
-        
+        if ( (d = do_createdomain(dom, pro)) != NULL )
+            ret = 0;
+        
+    alloc_out:
+        spin_unlock(&alloc_lock);
+
         op->u.createdomain.domain = d->domain_id;
         copy_to_user(u_dom0_op, op, sizeof(*op));
     }

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