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

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Date:   Tue, 4 Jul 2023 10:28:36 -0600
From:   Keith Busch <kbusch@...nel.org>
To:     Jan Kara <jack@...e.cz>
Cc:     linux-block@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        Jens Axboe <axboe@...nel.dk>,
        Christoph Hellwig <hch@...radead.org>,
        Alasdair Kergon <agk@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Anna Schumaker <anna@...nel.org>, Chao Yu <chao@...nel.org>,
        Christian Borntraeger <borntraeger@...ux.ibm.com>,
        "Darrick J. Wong" <djwong@...nel.org>,
        Dave Kleikamp <shaggy@...nel.org>,
        David Sterba <dsterba@...e.com>, dm-devel@...hat.com,
        drbd-dev@...ts.linbit.com, Gao Xiang <xiang@...nel.org>,
        Jack Wang <jinpu.wang@...os.com>,
        Jaegeuk Kim <jaegeuk@...nel.org>,
        jfs-discussion@...ts.sourceforge.net,
        Joern Engel <joern@...ybastard.org>,
        Joseph Qi <joseph.qi@...ux.alibaba.com>,
        Kent Overstreet <kent.overstreet@...il.com>,
        linux-bcache@...r.kernel.org, linux-btrfs@...r.kernel.org,
        linux-erofs@...ts.ozlabs.org, linux-ext4@...r.kernel.org,
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        linux-mtd@...ts.infradead.org, linux-nfs@...r.kernel.org,
        linux-nilfs@...r.kernel.org, linux-nvme@...ts.infradead.org,
        linux-pm@...r.kernel.org, linux-raid@...r.kernel.org,
        linux-s390@...r.kernel.org, linux-scsi@...r.kernel.org,
        linux-xfs@...r.kernel.org,
        "Md. Haris Iqbal" <haris.iqbal@...os.com>,
        Mike Snitzer <snitzer@...nel.org>,
        Minchan Kim <minchan@...nel.org>, ocfs2-devel@....oracle.com,
        reiserfs-devel@...r.kernel.org,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        Song Liu <song@...nel.org>,
        Sven Schnelle <svens@...ux.ibm.com>,
        target-devel@...r.kernel.org, Ted Tso <tytso@....edu>,
        Trond Myklebust <trond.myklebust@...merspace.com>,
        xen-devel@...ts.xenproject.org
Subject: Re: [PATCH 01/32] block: Provide blkdev_get_handle_* functions

On Tue, Jul 04, 2023 at 02:21:28PM +0200, Jan Kara wrote:
> +struct bdev_handle *blkdev_get_handle_by_dev(dev_t dev, blk_mode_t mode,
> +		void *holder, const struct blk_holder_ops *hops)
> +{
> +	struct bdev_handle *handle = kmalloc(sizeof(struct bdev_handle),
> +					     GFP_KERNEL);

I believe 'sizeof(*handle)' is the preferred style.

> +	struct block_device *bdev;
> +
> +	if (!handle)
> +		return ERR_PTR(-ENOMEM);
> +	bdev = blkdev_get_by_dev(dev, mode, holder, hops);
> +	if (IS_ERR(bdev))
> +		return ERR_CAST(bdev);

Need a 'kfree(handle)' before the error return. Or would it be simpler
to get the bdev first so you can check the mode settings against a
read-only bdev prior to the kmalloc?

> +	handle->bdev = bdev;
> +	handle->holder = holder;
> +	return handle;
> +}
> +EXPORT_SYMBOL(blkdev_get_handle_by_dev);
> +
>  /**
>   * blkdev_get_by_path - open a block device by name
>   * @path: path to the block device to open
> @@ -884,6 +902,28 @@ struct block_device *blkdev_get_by_path(const char *path, blk_mode_t mode,
>  }
>  EXPORT_SYMBOL(blkdev_get_by_path);
>  
> +struct bdev_handle *blkdev_get_handle_by_path(const char *path, blk_mode_t mode,
> +		void *holder, const struct blk_holder_ops *hops)
> +{
> +	struct bdev_handle *handle;
> +	dev_t dev;
> +	int error;
> +
> +	error = lookup_bdev(path, &dev);
> +	if (error)
> +		return ERR_PTR(error);
> +
> +	handle = blkdev_get_handle_by_dev(dev, mode, holder, hops);
> +	if (!IS_ERR(handle) && (mode & BLK_OPEN_WRITE) &&
> +	    bdev_read_only(handle->bdev)) {
> +		blkdev_handle_put(handle);
> +		return ERR_PTR(-EACCES);
> +	}
> +
> +	return handle;
> +}
> +EXPORT_SYMBOL(blkdev_get_handle_by_path);