[PATCH v5 11/14] block: update __register_blkdev() probe documentation

From: Luis Chamberlain <mcgrof@kernel.org>
To: axboe@kernel.dk, hch@lst.de, penguin-kernel@i-love.sakura.ne.jp,
	dan.j.williams@intel.com, vishal.l.verma@intel.com,
	dave.jiang@intel.com, ira.weiny@intel.com, richard@nod.at,
	miquel.raynal@bootlin.com, vigneshr@ti.com, efremov@linux.com,
	song@kernel.org, martin.petersen@oracle.com, hare@suse.de,
	jack@suse.cz, ming.lei@redhat.com, tj@kernel.org,
	mcgrof@kernel.org
Cc: linux-mtd@lists.infradead.org, linux-scsi@vger.kernel.org,
	linux-raid@vger.kernel.org, linux-block@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: [PATCH v5 11/14] block: update __register_blkdev() probe documentation
Date: Wed,  3 Nov 2021 16:04:34 -0700	[thread overview]
Message-ID: <20211103230437.1639990-12-mcgrof@kernel.org> (raw)
In-Reply-To: <20211103230437.1639990-1-mcgrof@kernel.org>

__register_blkdev() is used to register a probe callback, and
that callback is typically used to call add_disk(). Now that
we are able to capture errors for add_disk(), we need to fix
those probe calls where add_disk() fails and clean up resources.

We don't extend the probe call to return the error given:

1) we'd have to always special-case the case where the disk
   was already present, as otherwise concurrent requests to
   open an existing block device would fail, and this would be
   a userspace visible change
2) the error from ilookup() on blkdev_get_no_open() is sufficient
3) The only thing the probe call is used for is to support
   pre-devtmpfs, pre-udev semantics that want to create disks when
   their pre-created device node is accessed, and so we don't care
   for failures on probe there.

Expand documentation for the probe callback to ensure users cleanup
resources if add_disk() is used and to clarify this interface may be
removed in the future.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>
---
 block/genhd.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/block/genhd.c b/block/genhd.c
index 4ed87f25276a..2f5b7e24e88a 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -213,7 +213,10 @@ void blkdev_show(struct seq_file *seqf, off_t offset)
  * @major: the requested major device number [1..BLKDEV_MAJOR_MAX-1]. If
  *         @major = 0, try to allocate any unused major number.
  * @name: the name of the new block device as a zero terminated string
- * @probe: allback that is called on access to any minor number of @major
+ * @probe: pre-devtmpfs / pre-udev callback used to create disks when their
+ *	   pre-created device node is accessed. When a probe call uses
+ *	   add_disk() and it fails the driver must cleanup resources. This
+ *	   interface may soon be removed.
  *
  * The @name must be unique within the system.
  *
-- 
2.33.0

