linux-kernel - Re: [PATCH v2 6/8] bdev: add open

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Date:   Wed, 23 Oct 2019 19:22:32 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Michal Suchanek <msuchanek@...e.de>
Cc:     linux-scsi@...r.kernel.org, Jonathan Corbet <corbet@....net>,
        Jens Axboe <axboe@...nel.dk>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Mauro Carvalho Chehab <mchehab+samsung@...nel.org>,
        Eric Biggers <ebiggers@...gle.com>,
        "J. Bruce Fields" <bfields@...hat.com>,
        Benjamin Coddington <bcodding@...hat.com>,
        Hannes Reinecke <hare@...e.com>,
        Omar Sandoval <osandov@...com>, Ming Lei <ming.lei@...hat.com>,
        Damien Le Moal <damien.lemoal@....com>,
        Bart Van Assche <bvanassche@....org>,
        Tejun Heo <tj@...nel.org>, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH v2 6/8] bdev: add open_finish.

On Wed, Oct 23, 2019 at 02:52:45PM +0200, Michal Suchanek wrote:
> Opening a block device may require a long operation such as waiting for
> the cdrom tray to close. Performing this operation with locks held locks
> out other attempts to open the device. These processes waiting to open
> the device are not killable.
> 
> To avoid this issue and still be able to perform time-consuming checks
> at open() time the block device driver can provide open_finish(). If it
> does opening the device proceeds even when an error is returned from
> open(), bd_mutex is released and open_finish() is called. If
> open_finish() succeeds the device is now open, if it fails release() is
> called.
> 
> When -ERESTARTSYS is returned from open() blkdev_get may loop without
> calling open_finish(). On -ERESTARTSYS open_finish() is not called.
> 
> Move a ret = 0 assignment up in the if/else branching to avoid returning
> -ENXIO. Previously the return value was ignored on the unhandled branch.

This just doesn't make much sense.  There is no point in messing up
the block API for ugly workarounds like that.