Re: [PATCH v2] documentation: fix Generic Block Device Capability

From: Fabio Fantoni
Date: Tue Jan 17 2023 - 10:52:40 EST

Il 17/01/2023 07:05, Christoph Hellwig ha scritto:
On Mon, Jan 16, 2023 at 07:14:41PM +0100, Fabio Fantoni wrote:
Il 16/01/2023 18:53, Christoph Hellwig ha scritto:
On Tue, Jan 10, 2023 at 02:21:04PM +0100, Fabio Fantoni wrote:
- * ``GENHD_FL_REMOVABLE``: indicates that the block device gives access to
+ * ``GENHD_FL_REMOVABLE`` (0x01): indicates that the block device gives access to
The numberic values really do not belong into the documentation. They
are just implementation details.

Thanks for reply, if values are not into the documentation see from
/sys/block/<disk>/capability output what flags are enabled will require look
to source code of include/linux/blkdev.h and
Documentation/block/capability.rst will be less useful, or I'm wrong?
Urgg. I think this file is generally just a bad idea. The flags are
kernel internal and not isolated from userspace. It seems nothing broke
with the various renumbering lately, but we need to isolate it from
the implementation details. And if it really should be a user API
we need a text version of it.

Up to 5.13 the page was "ok" (https://www.kernel.org/doc/html/v5.13/block/capability.html) from 5.14 doc comments of other functions was appaired, from 5.17 the flags had "major" changes and values was removed from doc comment (https://www.kernel.org/doc/html/v5.17/block/capability.html)

With this patch return to have only block capability flags in this file and including the values: https://snipboard.io/QrN6hg.jpg

But as you tell that this file is a bad idea, Documentation/block/capability.rst should be removed?

About if should be a user API, I don't have enough experience to be able to say if and in which cases it could be useful on the user side. From what I could see with the documentation page correct is that you can at least immediately see (after a very fast search) for example if the block device is removable and if it is partitionable. And even if the values was changed pointing to the doc page of the used kernel version and having the values in doc is still possible see what flags are enabled from doc page.