Re: [rfc][patch 3/4] fs: new truncate sequence

Nick Piggin
2009-07-08T06:32:36Z

On Tue, Jul 07, 2009 at 12:30:42PM -0400, Christoph Hellwig wrote:
> On Tue, Jul 07, 2009 at 05:48:09PM +0200, Nick Piggin wrote:
> > OK, so what do you suggest? If the filesystem defines
> > ->setsize then do not pass ATTR_SIZE changes into setattr?
> > But then do you also not pass in ATTR_TIME cchanges to setattr
> > iff they are together with ATTR_SIZE change? It sees also like
> > quite a difficult calling convention.
>
> Ok, I played around with these ideas and your patches a bit. I think
> we're actually best of to return to one of the early ideas and just
> get rid of ->truncate without any replacement, e.g. let ->setattr
> handle all of it.

Yes I do agree. ->setsize inside inode_setattr would have been
OK as wel I think, but this is probably even cleaner even though
it might be a bit more work.

> Below is a patch ontop of you four patches that implements exactly that
> and it looks surprisingly nice. The only gotcha I can see is that we
> need to audit for existing filesystems not implementing ->truncate
> getting a behaviour change due to the checks to decide if we want
> to call vmtruncate. But most likely any existing filesystems without
> ->truncate using the buffer.c helper or direct I/O is buggy anyway.

Thanks for the patch, I think I will fold it in to the series. I
think we probably do need to call simple_setsize in inode_setattr
though (unless you propose to eventually convert every filesystem
to define a .setattr). This would also require eg. your ext2
conversion to strip ATTR_SIZE before passing through to inode_setattr.

We could just add some temporary field for example in the i_op
structure to test for and remove it when everybody is converted,
which woud guarantee back compatibility.

> Note that it doesn't touch i_alloc_mutex locking for now - if we go
> down this route I would do the lock shift in one patch at the end of
> the series.

Yeah fine by me (or do it in a new series).

> int ext2_setattr(struct dentry *dentry, struct iattr *iattr)
> {
> struct inode *inode = dentry->d_inode;
> int error;
>
> + if (iattr->ia_valid & ATTR_SIZE) {
> + error = ext2_setsize(inode, iattr->ia_size);
> + if (error)
> + return error;
> + }
> +
> error = inode_change_ok(inode, iattr);
> if (error)
> return error;

Probably want to call inode_change_ok first here.