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Date:   Fri, 11 Aug 2023 15:56:34 -0700
From:   "Darrick J. Wong" <djwong@kernel.org>
To:     Kent Overstreet <kent.overstreet@linux.dev>
Cc:     Christian Brauner <brauner@kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
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        tytso@mit.edu, bfoster@redhat.com, jack@suse.cz,
        andreas.gruenbacher@gmail.com, peterz@infradead.org,
        akpm@linux-foundation.org, dhowells@redhat.com, snitzer@kernel.org,
        axboe@kernel.dk
Subject: Re: [GIT PULL] bcachefs
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On Fri, Aug 11, 2023 at 09:21:41AM -0400, Kent Overstreet wrote:
> On Fri, Aug 11, 2023 at 12:54:42PM +0200, Christian Brauner wrote:
> > > I don't want to do that to Christian either, I think highly of the work
> > > he's been doing and I don't want to be adding to his frustration. So I
> > > apologize for loosing my cool earlier; a lot of that was frustration
> > > from other threads spilling over.
> > > 
> > > But: if he's going to be raising objections, I need to know what his
> > > concerns are if we're going to get anywhere. Raising objections without
> > > saying what the concerns are shuts down discussion; I don't think it's
> > > unreasonable to ask people not to do that, and to try and stay focused
> > > on the code.
> > 
> > The technical aspects were made clear off-list and I believe multiple
> > times on-list by now. Any VFS and block related patches are to be
> > reviewed and accepted before bcachefs gets merged.
> 
> Here's the one VFS patch in the series - could we at least get an ack
> for this? It's a new helper, just breaks the existing d_tmpfile() up
> into two functions - I hope we can at least agree that this patch
> shouldn't be controversial?
> 
> -->--
> Subject: [PATCH] fs: factor out d_mark_tmpfile()
> 
> New helper for bcachefs - bcachefs doesn't want the
> inode_dec_link_count() call that d_tmpfile does, it handles i_nlink on
> its own atomically with other btree updates
> 
> Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
> Cc: Alexander Viro <viro@zeniv.linux.org.uk>
> Cc: Christian Brauner <brauner@kernel.org>
> Cc: linux-fsdevel@vger.kernel.org

Yes, we can finally clean up this braindamage in xfs_generic_create:

	if (tmpfile) {
		/*
		 * The VFS requires that any inode fed to d_tmpfile must
		 * have nlink == 1 so that it can decrement the nlink in
		 * d_tmpfile.  However, we created the temp file with
		 * nlink == 0 because we're not allowed to put an inode
		 * with nlink > 0 on the unlinked list.  Therefore we
		 * have to set nlink to 1 so that d_tmpfile can
		 * immediately set it back to zero.
		 */
		set_nlink(inode, 1);
		d_tmpfile(tmpfile, inode);
	}

Reviewed-by: Darrick J. Wong <djwong@kernel.org>

--D

> 
> diff --git a/fs/dcache.c b/fs/dcache.c
> index 52e6d5fdab..dbdafa2617 100644
> --- a/fs/dcache.c
> +++ b/fs/dcache.c
> @@ -3249,11 +3249,10 @@ void d_genocide(struct dentry *parent)
>  
>  EXPORT_SYMBOL(d_genocide);
>  
> -void d_tmpfile(struct file *file, struct inode *inode)
> +void d_mark_tmpfile(struct file *file, struct inode *inode)
>  {
>  	struct dentry *dentry = file->f_path.dentry;
>  
> -	inode_dec_link_count(inode);
>  	BUG_ON(dentry->d_name.name != dentry->d_iname ||
>  		!hlist_unhashed(&dentry->d_u.d_alias) ||
>  		!d_unlinked(dentry));
> @@ -3263,6 +3262,15 @@ void d_tmpfile(struct file *file, struct inode *inode)
>  				(unsigned long long)inode->i_ino);
>  	spin_unlock(&dentry->d_lock);
>  	spin_unlock(&dentry->d_parent->d_lock);
> +}
> +EXPORT_SYMBOL(d_mark_tmpfile);
> +
> +void d_tmpfile(struct file *file, struct inode *inode)
> +{
> +	struct dentry *dentry = file->f_path.dentry;
> +
> +	inode_dec_link_count(inode);
> +	d_mark_tmpfile(file, inode);
>  	d_instantiate(dentry, inode);
>  }
>  EXPORT_SYMBOL(d_tmpfile);
> diff --git a/include/linux/dcache.h b/include/linux/dcache.h
> index 6b351e009f..3da2f0545d 100644
> --- a/include/linux/dcache.h
> +++ b/include/linux/dcache.h
> @@ -251,6 +251,7 @@ extern struct dentry * d_make_root(struct inode *);
>  /* <clickety>-<click> the ramfs-type tree */
>  extern void d_genocide(struct dentry *);
>  
> +extern void d_mark_tmpfile(struct file *, struct inode *);
>  extern void d_tmpfile(struct file *, struct inode *);
>  
>  extern struct dentry *d_find_alias(struct inode *);