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

Luis Chamberlain
2021-11-03T23:05:36Z

__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