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SubjectRe: [RFD 1/4] Pass no useless nameidata to the create, lookup, and permission IOPs
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On Saturday 30 June 2007 11:13, Christoph Hellwig wrote:
> We need something like this, but I don't quite like the way you've done
> it. First the name is wrong, it's not a nameidata anymore but a lookup
> intent, so it should be named that way, struct lookup_intent.

Sure, that name was pretty random ... lookup_intent has gotten the majority of
votes so far, and I'm perfectly fine with that.

> Second the macro hackery is more than ugly, please keep the structures
> separate. With modern gcc it might be possible to embed the lookup_intent
> into the nameidata anonymously.

http://gcc.gnu.org/onlinedocs/gcc-4.2.0/gcc/Unnamed-Fields.html

If we can add the -fms-extensions gcc option we can get rid of the macro, and
the code becomes pretty clean (as shown below). If we cannot add this option,
then gcc would puke on ``struct lookup_intent;'' in the definition of struct
nameidata. The macro is the cleanest way to work around this I could come up
with, but maybe somebody knows another trick.

--- a/include/linux/namei.h
+++ b/include/linux/namei.h
@@ -14,14 +14,10 @@ struct open_intent {

enum { MAX_NESTED_LINKS = 8 };

-struct nameidata {
+struct lookup_intent {
struct dentry *dentry;
struct vfsmount *mnt;
- struct qstr last;
unsigned int flags;
- int last_type;
- unsigned depth;
- char *saved_names[MAX_NESTED_LINKS + 1];

/* Intent data */
union {
@@ -29,6 +25,19 @@ struct nameidata {
} intent;
};

+struct nameidata {
+ struct lookup_intent;
+ struct qstr last;
+ int last_type;
+ unsigned depth;
+ char *saved_names[MAX_NESTED_LINKS + 1];
+};

> Also please either remove the dentry from struct lookup_entry or from the
> direct argument list of the functions and methods - there is no need to pass
> this one twice.

The dentry in the lookup_intent of the create inode operation is the parent
dentry right now, and the child dentry is passed as the separate parameter. I
would prefer the cleaner interface in which the lookup_intent refers to the
child dentry as well. (Getting from the child to the parent is trivial.) I
guess this can go in an incremental patch with the next version of these
patches.

Thanks,
Andreas
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