linux-kernel - Re: [PATCH 0/3} Change ->mkdir() and vfs

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Message-ID: <20250214060039.GB1977892@ZenIV>
Date: Fri, 14 Feb 2025 06:00:39 +0000
From: Al Viro <viro@...iv.linux.org.uk>
To: NeilBrown <neilb@...e.de>
Cc: Christian Brauner <brauner@...nel.org>,
	Trond Myklebust <trondmy@...nel.org>,
	Anna Schumaker <anna@...nel.org>, linux-nfs@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/3} Change ->mkdir() and vfs_mkdir() to return a dentry

On Fri, Feb 14, 2025 at 04:16:40PM +1100, NeilBrown wrote:
> 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 operation 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 NFS in particular
> to return the correct dentry (I believe it is the only filesystem to
> possibly not use the given dentry), and changes vfs_mkdir() to return
> that dentry, removing the look that a few callers currently need.
> 
> I have not Cc: the developers of all the individual filesystems - only
> NFS.  I have build-tested all the changes except hostfs.  I can email
> them explicitly if/when this is otherwise acceptable.  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.

1) please, don't sprinkle the PTR_ERR_OR_ZERO() shite all over the place.
Almost always the same thing can be done without it and it ends up
being cleaner.  Seriously.

2) I suspect that having method instances return NULL for "just use the
argument" would would be harder to fuck up; basically, the same as for
->lookup() instances.  I'll try to tweak it and see what falls out...

3) I'm pretty sure that NFS is *not* the only filesystem that returns
unhashed negative in some success cases; will need to go over the instances
to verify that, though.