[Xen-devel] page_list_splice

[Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>]

Keir, Jan (or anybody familiar with the new page_list_* functions) --

I've implemented page_list_splice as below but I don't
think the second if clause should be necessary...  I'm
using it with this clause because it works for this case
which is nearly always true (splicing into the scrub_list
which is almost always empty).

Without this clause, I get a null-pointer (actually null+4) 
dereference... I think I must be missing some basic
difference between normal list code and page_list code.

Anyway, could you take a look at the routine to see if
I've missed something obvious in the case where neither
page_list parameter is empty?  It's tough to reproduce
this condition and you might be able to see a bug
on inspection.  (Or maybe the differences between normal
list code and page_list code require the extra
page_list_empty check and this code will work properly
regardless of whether one or both page_list is empty.)

Thanks,
Dan

P.S. In case its not obvious, I started from list_splice
in list.h

==============

diff -r 4ac8bc60c000 xen/include/xen/mm.h
--- a/xen/include/xen/mm.h      Tue Feb 10 05:51:00 2009 +0000
+++ b/xen/include/xen/mm.h      Thu Mar 05 13:06:42 2009 -0700
@@ -219,6 +221,32 @@ page_list_remove_head(struct page_list_h
     return page;
 }
 
+static inline void
+page_list_splice(struct page_list_head *list, struct page_list_head *head)
+{
+    struct page_info *first, *last, *at;
+
+    if ( page_list_empty(list) )
+        return;
+
+    if ( page_list_empty(head) )
+    {
+        head->next = list->next;
+        head->tail = list->tail;
+        return;
+    }
+
+    first = list->next;
+    last = list->tail;
+    at = head->next;
+
+    first->list.prev = page_to_mfn(head->next);
+    head->next = first;
+
+    last->list.next = page_to_mfn(at);
+    at->list.prev = page_to_mfn(last);
+}
+
 #define page_list_for_each(pos, head) \
     for ( pos = (head)->next; pos; pos = page_list_next(pos, head) )
 #define page_list_for_each_safe(pos, tmp, head) \

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