[PATCH][RESEND] don't allow sys_readahead() on files opened with O_DIRECT

[Jan Blunck <j.blunck@tu-harburg.de>]

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IMO sys_readahead() doesn't make sense if the file is opened with
O_DIRECT, because the page cache is stuffed but never used. Therefore
this patch changes that by letting the call return with -EINVAL.

Signed-off-by: Jan Blunck <j.blunck@tu-harburg.de>


[-- Attachment #2: filemap.c_direct_IO_readahead.diff --]
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 mm/filemap.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletion(-)

Index: experimental-jb/mm/filemap.c
===================================================================
--- experimental-jb.orig/mm/filemap.c
+++ experimental-jb/mm/filemap.c
@@ -1111,7 +1111,8 @@ static ssize_t
 do_readahead(struct address_space *mapping, struct file *filp,
 	     unsigned long index, unsigned long nr)
 {
-	if (!mapping || !mapping->a_ops || !mapping->a_ops->readpage)
+	if (!mapping || !mapping->a_ops || !mapping->a_ops->readpage
+	    || (filp->f_flags & O_DIRECT))
 		return -EINVAL;
 
 	force_page_cache_readahead(mapping, filp, index,