linux-ext4 - Re: [PATCH 01/32] block: Provide blkdev_get_handle

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Message-ID: <20230705161225.cwig5a3mo6oz7lew@quack3>
Date:   Wed, 5 Jul 2023 18:12:25 +0200
From:   Jan Kara <jack@...e.cz>
To:     Bart Van Assche <bvanassche@....org>
Cc:     Jan Kara <jack@...e.cz>, linux-block@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, Jens Axboe <axboe@...nel.dk>,
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Subject: Re: [PATCH 01/32] block: Provide blkdev_get_handle_* functions

On Tue 04-07-23 07:06:26, Bart Van Assche wrote:
> On 7/4/23 05:21, Jan Kara wrote:
> > +struct bdev_handle {
> > +	struct block_device *bdev;
> > +	void *holder;
> > +};
> 
> Please explain in the patch description why a holder pointer is introduced
> in struct bdev_handle and how it relates to the bd_holder pointer in struct
> block_device. Is one of the purposes of this patch series perhaps to add
> support for multiple holders per block device?

No. The reason for adding holder to struct bdev_handle is that it is an
argument blkdev_put() needs. Currently, every user of blkdev_put() has to
remember what it has passed as 'holder' to blkdev_get_by_*() call and pass
that to blkdev_put(). With struct bdev_handle this will happen
automatically. This is already explained in the changelog of this patch:

"Create struct bdev_handle that contains all parameters that need to be
passed to blkdev_put()..."

If it was only about holder, the intrusive patches would not be warranted
but as the description also says:

"This will eventually allow us to pass one more argument to blkdev_put()
without too much hassle."

Because we will additionaly need to propagate the 'mode' argument used at
open to blkdev_put().

								Honza

-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR