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

["Theodore Ts'o" <tytso@mit.edu>]

On Thu, Feb 19, 2004 at 11:48:50AM -0800, Linus Torvalds wrote:
> Let's leave the "check_or_create_name()" thing for now, and see how we can
> use this in user space (and realize that we only do this on cache failure,
> so this is the "slow case"):
> 
> 	set_bit_one(dir);
> 	lseek(dir, 0, SEEK_SET);
> 	while (readdir(dir, de)) {
> 		stat(de->d_name);
> 		.. might also compare the name here with whatever it is 
> 		   working on right now..
> 	}
> 	set_bit_two_if_one_is_set(dirfd);
> 
> Notice what the above does? After the above loop, bit two will be set IFF 
> the dentry cache now contains every single name in the directory. 
> Otherwise it will be clear. Bit two will basically be a "dcache complete" 
> bit.

Why do this in user space?  The set_bit_one() and
set_bit_two_if_one_is_set() can't really be used for anything else,
really, so why not let check_or_create_name() do the above loop if
necessary to populate all of the dcache entries in the dentry cache?

That way we only expose one system call (check_or_create_name()), and
we let the internal dcache flags be an internal implementation detail.
It will also make it much easier to avoid races.

						- Ted