linux-kernel - Re: [PATCH 1/6] Change inode_operations.mkdir to return struct dentry *

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Message-id: <174036084630.74271.16513912864596248299@noble.neil.brown.name>
Date: Mon, 24 Feb 2025 12:34:06 +1100
From: "NeilBrown" <neilb@...e.de>
To: "Al Viro" <viro@...iv.linux.org.uk>
Cc: "Christian Brauner" <brauner@...nel.org>, "Jan Kara" <jack@...e.cz>,
 "Miklos Szeredi" <miklos@...redi.hu>, "Xiubo Li" <xiubli@...hat.com>,
 "Ilya Dryomov" <idryomov@...il.com>, "Richard Weinberger" <richard@....at>,
 "Anton Ivanov" <anton.ivanov@...bridgegreys.com>,
 "Johannes Berg" <johannes@...solutions.net>,
 "Trond Myklebust" <trondmy@...nel.org>, "Anna Schumaker" <anna@...nel.org>,
 "Chuck Lever" <chuck.lever@...cle.com>, "Jeff Layton" <jlayton@...nel.org>,
 "Olga Kornievskaia" <okorniev@...hat.com>, "Dai Ngo" <Dai.Ngo@...cle.com>,
 "Tom Talpey" <tom@...pey.com>,
 "Sergey Senozhatsky" <senozhatsky@...omium.org>,
 linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-cifs@...r.kernel.org, linux-nfs@...r.kernel.org,
 linux-um@...ts.infradead.org, ceph-devel@...r.kernel.org,
 netfs@...ts.linux.dev
Subject:
 Re: [PATCH 1/6] Change inode_operations.mkdir to return struct dentry *

On Sat, 22 Feb 2025, Al Viro wrote:
> On Fri, Feb 21, 2025 at 10:36:30AM +1100, NeilBrown wrote:
> 
> > +In general, filesystems which use d_instantiate_new() to install the new
> > +inode can safely return NULL.  Filesystems which may not have an I_NEW inode
> > +should use d_drop();d_splice_alias() and return the result of the latter.
> 
> IMO that's a bad pattern, _especially_ if you want to go for "in-update"
> kind of stuff later.

Agreed.  I have a draft patch to change d_splice_alias() and
d_exact_alias() to work on hashed dentrys.  I thought it should go after
these mkdir patches rather than before.

Thanks,
NeilBrown


> 
> That's pretty much the same thing as d_drop()/d_rehash() window.
> 
> We'd be better off dropping that BUG_ON() in d_splice_alias() and teaching
> __d_add() to handle the "it's a hashed negative" case.
>