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Date:   Tue, 9 May 2023 15:35:01 +0200
From:   Christoph Hellwig <hch@lst.de>
To:     "Darrick J. Wong" <djwong@kernel.org>
Cc:     Christoph Hellwig <hch@lst.de>, Jens Axboe <axboe@kernel.dk>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Christian Brauner <brauner@kernel.org>,
        linux-block@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        linux-xfs@vger.kernel.org
Subject: Re: [PATCH 5/9] block: introduce holder ops
Message-ID: <20230509133501.GD841@lst.de>
References: <20230505175132.2236632-1-hch@lst.de> <20230505175132.2236632-6-hch@lst.de> <20230505185119.GI15394@frogsfrogsfrogs>
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On Fri, May 05, 2023 at 11:51:19AM -0700, Darrick J. Wong wrote:
> Fun question: What happens when the swap disk falls off the bus?

Your system is toast.

> > -	if (IS_ERR(blkdev_get_by_dev(bdev->bd_dev, mode | FMODE_EXCL, &bdev)))
> > +	if (IS_ERR(blkdev_get_by_dev(bdev->bd_dev, mode | FMODE_EXCL, &bdev,
> > +			NULL)))
> >  		return -EBUSY;
> >  	ret = set_blocksize(bdev, n);
> >  	blkdev_put(bdev, mode | FMODE_EXCL);
> 
> Somewhat related question: Should we allow userspace to initiate a fs
> shutdown through the block device?  Let's say you're preparing to yank
> /dev/sda and want to kill anything attached to it or its partitions?
> Without having to walk through however many mount namespaces there are
> to find the mountpoints?

That's kinda what we're doing here.  Or do you mean even more advanced
notice by having another callout before stopping I/O so that we could
write out all log buffers?  It's probably doable, but I'm not convinced
that this use case is worth maintaining and testing the kernel code for
it.