Re: Eureka! (was Re: UTF-8 and case-insensitivity)

[Linus Torvalds]

On Thu, 19 Feb 2004, Linus Torvalds wrote:
> 
> See? Nobody actually ever sees the "raw dentry". They all go through 
> __d_lookup(), and the rule would be:
> 
>  - if "d_lookup()" sees a tentative dentry, it will just unhash it and 
>    drop it (it has the dcache lock, so it can do that)
>  - all callers of "__d_lookup()" will have to check for D_TENTATIVE, and 
>    decide what to do with it. I think there are exactly _three_ callers, 
>    and one of them is d_lookup() itself.

Actually, I've got a better setup: instead of having a D_TENTATIVE flag in 
the dentry flags, just do

	#define TENTATIVE_INODE ((struct inode *) 1)

and just have "dentry->d_inode = TENTATIVE_INODE" for the dentries that 
were filled directly from "readdir()" data.

This not only avoids using a bit in the dentry flags, but it pretty much
guarantees that everybody is forced to use them correctly. It would be
very hard to have a buggy user: the dentry will clearly not be a negative
dentry (since d_inode is not NULL), but if anybody ever uses it as a
positive dentry, you'll get a nice and immediate oops.

So we'd see very quickly if these tentative dentries were to escape 
outside of __d_lookup().

			Linus
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