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From:   Christoph Hellwig <hch@lst.de>
To:     Jens Axboe <axboe@kernel.dk>
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        "Rafael J. Wysocki" <rafael@kernel.org>,
        Denis Efremov <efremov@linux.com>,
        "David S. Miller" <davem@davemloft.net>,
        Song Liu <song@kernel.org>, Al Viro <viro@zeniv.linux.org.uk>,
        Finn Thain <fthain@telegraphics.com.au>,
        Michael Schmitz <schmitzmic@gmail.com>,
        linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-ide@vger.kernel.org, linux-raid@vger.kernel.org,
        linux-scsi@vger.kernel.org, linux-m68k@lists.linux-m68k.org
Subject: simplify gendisk lookup and remove struct block_device aliases v4
Date:   Thu, 29 Oct 2020 15:58:23 +0100
Message-Id: <20201029145841.144173-1-hch@lst.de>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

Hi all,

this series removes the annoying struct block_device aliases, which can
happen for a bunch of old floppy drivers (and z2ram).  In that case
multiple struct block device instances for different dev_t's can point
to the same gendisk, without being partitions.  The cause for that
is the probe/get callback registered through blk_register_regions.

This series removes blk_register_region entirely, splitting it it into
a simple xarray lookup of registered gendisks, and a probe callback
stored in the major_names array that can be used for modprobe overrides
or creating devices on demands when no gendisk is found.  The old
remapping is gone entirely, and instead the 4 remaining drivers just
register a gendisk for each operating mode.  In case of the two drivers
that have lots of aliases that is done on-demand using the new probe
callback, while for the other two I simply register all at probe time
to keep things simple.

Note that the m68k drivers are compile tested only.

Changes since v3:
 - keep kobj_map for char dev lookup for now, as the testbot found
   some very strange and unexplained regressions, so I'll get back to
   this later separately
 - fix a commit message typo

Changes since v2:
 - fix a wrong variable passed to ERR_PTR in the floppy driver
 - slightly adjust the del_gendisk cleanups to prepare for the next
   series touching this area

Changes since v1:
 - add back a missing kobject_put in the cdev code
 - improve the xarray delete loops