linux-kernel - [PATCH v4 1/4] block: update __register

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Message-Id: <20211103181258.1462704-2-mcgrof@kernel.org>
Date:   Wed,  3 Nov 2021 11:12:55 -0700
From:   Luis Chamberlain <mcgrof@...nel.org>
To:     axboe@...nel.dk, hch@....de, penguin-kernel@...ove.sakura.ne.jp,
        dan.j.williams@...el.com, vishal.l.verma@...el.com,
        dave.jiang@...el.com, ira.weiny@...el.com, richard@....at,
        miquel.raynal@...tlin.com, vigneshr@...com, efremov@...ux.com,
        song@...nel.org, martin.petersen@...cle.com, hare@...e.de,
        jack@...e.cz, ming.lei@...hat.com, tj@...nel.org, mcgrof@...nel.org
Cc:     linux-mtd@...ts.infradead.org, linux-scsi@...r.kernel.org,
        linux-raid@...r.kernel.org, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH v4 1/4] block: update __register_blkdev() probe documentation

__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.

Signed-off-by: Luis Chamberlain <mcgrof@...nel.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