linux-kernel - Re: [RFC PATCH V2 07/12] fs: Add locking for a dynamic inode 'mode'

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Message-ID: <20200116054040.GC8235@magnolia>
Date:   Wed, 15 Jan 2020 21:40:40 -0800
From:   "Darrick J. Wong" <darrick.wong@...cle.com>
To:     Ira Weiny <ira.weiny@...el.com>
Cc:     linux-kernel@...r.kernel.org,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Dan Williams <dan.j.williams@...el.com>,
        Dave Chinner <david@...morbit.com>,
        Christoph Hellwig <hch@....de>,
        "Theodore Y. Ts'o" <tytso@....edu>, Jan Kara <jack@...e.cz>,
        linux-ext4@...r.kernel.org, linux-xfs@...r.kernel.org,
        linux-fsdevel@...r.kernel.org
Subject: Re: [RFC PATCH V2 07/12] fs: Add locking for a dynamic inode 'mode'

On Wed, Jan 15, 2020 at 11:08:46AM -0800, Ira Weiny wrote:
> On Mon, Jan 13, 2020 at 05:03:22PM -0800, Darrick J. Wong wrote:
> > On Mon, Jan 13, 2020 at 04:20:05PM -0800, Ira Weiny wrote:
> > > On Mon, Jan 13, 2020 at 02:12:18PM -0800, Darrick J. Wong wrote:
> > > > On Fri, Jan 10, 2020 at 11:29:37AM -0800, ira.weiny@...el.com wrote:
> > > > > From: Ira Weiny <ira.weiny@...el.com>
> 
> [snip]
> 
> > > > > +``lock_mode``
> > > > > +	called to prevent operations which depend on the inode's mode from
> > > > > +        proceeding should a mode change be in progress
> > > > 
> > > > "Inodes can't change mode, because files do not suddenly become
> > > > directories". ;)
> > > 
> > > Yea sorry.
> > > 
> > > > 
> > > > Oh, you meant "lock_XXXX is called to prevent a change in the pagecache
> > > > mode from proceeding while there are address space operations in
> > > > progress".  So these are really more aops get and put functions...
> > > 
> > > At first I actually did have aops get/put functions but this is really
> > > protecting more than the aops vector because as Christoph said there are file
> > > operations which need to be protected not just address space operations.
> > > 
> > > But I agree "mode" is a bad name...  Sorry...
> > 
> > inode_fops_{get,set}(), then?
> > 
> > inode_start_fileop()
> > inode_end_fileop() ?
> > 
> > Trying to avoid sounding foppish <COUGH>
> 
> What about?
> 
> inode_[un]lock_state()?

Kinda vague -- which state?  inodes retain a lot of different state.

This locking primitive ensures that file operations pointers can't
change while any operations are ongoing, right?

--D

> Ira
>