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Date:   Mon, 4 Nov 2019 16:17:27 -0800
From:   Christoph Hellwig <hch@infradead.org>
To:     Michal Suchanek <msuchanek@suse.de>
Cc:     linux-scsi@vger.kernel.org, Christoph Hellwig <hch@infradead.org>,
        Matthew Wilcox <willy@infradead.org>,
        "Ewan D. Milne" <emilne@redhat.com>,
        Jonathan Corbet <corbet@lwn.net>, Jens Axboe <axboe@kernel.dk>,
        "James E.J. Bottomley" <jejb@linux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@oracle.com>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        "J. Bruce Fields" <bfields@redhat.com>,
        Mauro Carvalho Chehab <mchehab+samsung@kernel.org>,
        Eric Biggers <ebiggers@google.com>,
        Benjamin Coddington <bcodding@redhat.com>,
        Hannes Reinecke <hare@suse.com>,
        Omar Sandoval <osandov@fb.com>, Ming Lei <ming.lei@redhat.com>,
        Damien Le Moal <damien.lemoal@wdc.com>,
        Bart Van Assche <bvanassche@acm.org>,
        Tejun Heo <tj@kernel.org>, linux-doc@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH v3 5/7] bdev: add open_finish.
Message-ID: <20191105001727.GA29826@infradead.org>
References: <cover.1572002144.git.msuchanek@suse.de>
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Please make sure you CC linux-block if you add block device ops.

On Fri, Oct 25, 2019 at 01:21:42PM +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.

Still a complete nack for splitting a fundamental operation over two
ops, especially just for working around a piece of buggy software.