Re: [Xen-devel] Re: [Xen-changelog] [xen-unstable] stubdom: mmap on /dev/mem support

[Samuel Thibault <samuel.thibault@xxxxxxxxxxxx>]

Optimize mmap(open("/dev/mem"))

Set map_frames_ex's stride parameter to 0 and increment to 1 to avoid
building an explicit list of mfns.

Signed-Off-By: Samuel Thibault <samuel.thibault@xxxxxxxxxxxx>

diff -r 37829fd7c1e3 extras/mini-os/lib/sys.c
--- a/extras/mini-os/lib/sys.c  Wed Oct 21 16:08:28 2009 +0100
+++ b/extras/mini-os/lib/sys.c  Wed Oct 21 18:10:33 2009 +0200
@@ -1256,11 +1268,8 @@
         unsigned long zero = 0;
         return map_frames_ex(&zero, n, 0, 0, 1, DOMID_SELF, 0, 0);
     } else if (files[fd].type == FTYPE_MEM) {
-        int i;
-        unsigned long mfns[n];
-        for (i = 0; i < n; i++)
-            mfns[i] = ((unsigned long) offset + (i * PAGE_SIZE)) >> PAGE_SHIFT;
-        return map_frames_ex(mfns, n, 1, 0, 1, DOMID_IO, 0, 
_PAGE_PRESENT|_PAGE_RW);
+        unsigned long first_mfn = offset >> PAGE_SHIFT;
+        return map_frames_ex(&first_mfn, n, 0, 1, 1, DOMID_IO, 0, 
_PAGE_PRESENT|_PAGE_RW);
     } else ASSERT(0);
 }
 

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