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SubjectRe: tmpfs, NFS, file handles
On Wednesday February 20, braam@clusterfs.com wrote:
> Hi,
>
> > "Peter J. Braam" wrote:
> ...
> > > Is there a suggested solution for fh_to_dentry and dentry_to_fh for
> > > tmpfs?
> > >
> > > An "iget" based solution might work but at present tmpfs inodes are
> > > not hashed.
> On Wed, Feb 20, 2002 at 11:56:40AM -0500, Jeff Garzik wrote:
> ...
> > I talked to neil brown about NFS and ramfs... he mentioned using
> > iunique()
... but Trond had a better idea....

>
> So do I understand that hashing tmpfs inodes is perhaps the way to go?
>
> Would the following also work?
>
> - have a 32 bit counter: set inode->i_ino to count++
> - up the generation number each time the counter warps.

You don't just need a number in inode->i_ino. You also need to be
able to find an inode given that number.
So you need to store all the inodes in a hash table.
But you don't want to penalise non-NFS users.

I would probably:
leave i_ino as set by new_inode
initialise inode->i_generation to CURRENT_TIME

in dentry_to_fh,
check if list_empty(&inode->i_hash)
if it is, then add the inode to some hash table indexed by the
address of the inode
put the address of the inode, i_ino and i_generation in the filehandle

in fh_to_dentry,
lookup the given address in the hash table.
if it is found, check the i_ino and i_generation


That means you are only hashing inodes exported by NFS, and you have
a pretty good guarantee of uniqueness (providing time doesn't go
backwards).

NeilBrown
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