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Date: Mon, 29 Jan 2024 17:49:34 +0100
From: Christoph Hellwig <hch@lst.de>
To: Christian Brauner <brauner@kernel.org>
Cc: Jan Kara <jack@suse.cz>, Christoph Hellwig <hch@lst.de>,
	Jens Axboe <axboe@kernel.dk>, "Darrick J. Wong" <djwong@kernel.org>,
	linux-fsdevel@vger.kernel.org, linux-block@vger.kernel.org
Subject: Re: [PATCH v2 31/34] block: use file->f_op to indicate restricted
 writes
Message-ID: <20240129164934.GA4587@lst.de>
References: <20240123-vfs-bdev-file-v2-0-adbd023e19cc@kernel.org> <20240123-vfs-bdev-file-v2-31-adbd023e19cc@kernel.org>
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On Tue, Jan 23, 2024 at 02:26:48PM +0100, Christian Brauner wrote:
> Make it possible to detected a block device that was opened with
> restricted write access solely based on its file operations that it was
> opened with. This avoids wasting an FMODE_* flag.
> 
> def_blk_fops isn't needed to check whether something is a block device
> checking the inode type is enough for that. And def_blk_fops_restricted
> can be kept private to the block layer.

I agree with not wasting a FMODE_* flag, but I also really hate
duplicating the file operations.

I went to search for a good place to stash this information and ended up
at the f_version field in struct file.  That one is never touched by the 
VFS proper but just the file system and a few lseek helpers.  The
latter currently happen to be used by block devices unfortunately,
but it seem like moving the f_version clearing into the few filesystem
actualy using it would be good code hygiene anyway.