[uml-devel] force O_DIRECT inside UML

[Steve S. <sn...@fr...>]

Here is a little patch for all files opening that happen inside UML to be in  
O_DIRECT mode.

This is done to bypass the filecache inside the UML, since it's already done 
by the host.

I just hope it won't break anything, if so, please tell me
[ u can even yell... my /dev/null isn't full... yet.. ]

Btw, if it really works (aka doesn't crash and is helpful), i'll manage a 
configure option.

My big question is : is that enough ? [ i mean, if it really is, why nobody has 
thought of it before... so in other words, where is my mistake ? ]

--- linux-2.4.19/fs/open.c      Sat Aug  3 02:39:45 2002
+++ linux-2.4.19-snide/fs/open.c   Thu Nov  7 15:35:17 2002
@@ -805,6 +805,13 @@
 #if BITS_PER_LONG != 32
        flags |= O_LARGEFILE;
 #endif
+#ifdef CONFIG_USERMODE
+/*
+ * Inside UML, we don't want to go through pagecache since
+ * things will already be cached on the host
+ */
+       flags |= O_DIRECT;
+#endif
        tmp = getname(filename);
        fd = PTR_ERR(tmp);
        if (!IS_ERR(tmp)) {

  Steve

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