linux-kernel - Re: [PATCH] block: annotate bdev_disk_changed() deprecation with a symbol namespace

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Message-ID: <ZCIgavqUnw0Z3A3t@bombadil.infradead.org>
Date:   Mon, 27 Mar 2023 16:02:02 -0700
From:   Luis Chamberlain <mcgrof@...nel.org>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     axboe@...nel.dk, sth@...ux.ibm.com, hoeppner@...ux.ibm.com,
        hca@...ux.ibm.com, gor@...ux.ibm.com, agordeev@...ux.ibm.com,
        borntraeger@...ux.ibm.com, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] block: annotate bdev_disk_changed() deprecation with a
 symbol namespace

On Mon, Mar 27, 2023 at 03:16:39PM -0700, Christoph Hellwig wrote:
> On Mon, Mar 27, 2023 at 11:44:10AM -0700, Luis Chamberlain wrote:
> > Instead of relying on fragile documentation which can easily let us
> > slip, use a symbol namespace to annotate which symbols should not be
> > used by others.
> > 
> > This ensures no other users pop up by mistake easily and provides
> > us a with an easy vehicle to do the same with other routines should
> > we need it later.
> 
> I don't think deprecated really cuts it.  For these two drivers we
> can't really get rid of the calls as it is part of their ABI.

Ah yes.

> What I'd really want is something like an
> 
> EXPORT_SYMBOL_FOR(bdev_disk_changed, loop, CONFIG_BLK_DEV_LOOP);
> EXPORT_SYMBOL_FOR(bdev_disk_changed, dasd_kmod, CONFIG_DASD);
> 
> Which ensures that the symbol lookup only succeeds for loop.ko and
> dasd_kmod.ko, and that the export only happens if the relevant
> symbols are set.

I think that could be done, sure.

  Luis