linux-kernel - Re: [PATCH 0/3 RFC v2] change ->mkdir() and vfs

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Message-ID: <20250217-gummihammer-kryptisch-548d0dab31a3@brauner>
Date: Mon, 17 Feb 2025 11:47:08 +0100
From: Christian Brauner <brauner@...nel.org>
To: NeilBrown <neilb@...e.de>
Cc: Alexander Viro <viro@...iv.linux.org.uk>, Jan Kara <jack@...e.cz>, 
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/3 RFC v2] change ->mkdir() and vfs_mkdir() to return a
 dentry

On Mon, Feb 17, 2025 at 04:30:02PM +1100, NeilBrown wrote:
> Here is a second attempt at this change.  Guided by Al I have handled
> other file systems which don't return a hashed positive dentry on success.
> 
> It is not always possible to provide a reliable answer.  One example is
> that cifs might find, after successfully creating a directory, that the
> name now leads to a non-directory (due to a race with another client).
> So callers of vfs_mkdir() need to cope with successful mkdir but no
> usable dentry.  There is nothing they can do to recover and must
> continue gracefully.  This failre mode is detected by the returned
> dentry being unhashed.
> 
> ORIGINAL DESCRIPTION - updated to reflect changes.
> 
> This is a small set of patches which are needed before we can make the
> locking on directory operations more fine grained.  I think they are
> useful even if we don't go that direction.
> 
> Some callers of vfs_mkdir() need to operate on the resulting directory
> but cannot be guaranteed that the dentry will be hashed and positive on
> success - another dentry might have been used.
> 
> This patch changes ->mkdir to return a dentry, changes several

Thanks for doing that.

> filesystems to return the correct dentry, and changes vfs_mkdir() to
> return that dentry, only performing a lookup as a last resort.
> 
> I have not Cc: the developers of all the individual filesystems NFS.  I
> or kernel-test-robot have build-tested all the changes.  If anyone sees
> this on fs-devel and wants to provide a pre-emptive ack I will collect
> those and avoid further posting for those fs.

Once I'll merge this into async.dir it'll show up in fs-next which means
it'll get additional xfstest testing.