From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: "Rafał Miłecki" <zajec5@gmail.com>
Cc: "Srinivas Kandagatla" <srinivas.kandagatla@linaro.org>,
"Rafael J . Wysocki" <rafael@kernel.org>,
"Jonathan Corbet" <corbet@lwn.net>,
"Daniel Vetter" <daniel.vetter@ffwll.ch>,
"Dan Williams" <dan.j.williams@intel.com>,
"Bjorn Helgaas" <bhelgaas@google.com>,
"Krzysztof Wilczyński" <kw@linux.com>,
"Heiner Kallweit" <hkallweit1@gmail.com>,
linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
"Rafał Miłecki" <rafal@milecki.pl>
Subject: Re: [PATCH 2/2] nvmem: expose NVMEM cells in sysfs
Date: Tue, 21 Dec 2021 15:27:23 +0100 [thread overview]
Message-ID: <YcHkS0iDUhplbqUc@kroah.com> (raw)
In-Reply-To: <d626c2c2-5071-522f-330f-688254087d74@gmail.com>
On Tue, Dec 21, 2021 at 02:52:05PM +0100, Rafał Miłecki wrote:
> > How are nvmem devices named?
>
> $ ls /sys/bus/nvmem/devices/
> brcm-nvram0
> mtd0
> mtd1
> u-boot-envvar0
So no naming scheme at all.
{sigh}
> > > Example:
> > > $ cat /sys/bus/nvmem/devices/foo/cells/bootcmd
> > > tftp
> > > $ cat /sys/bus/nvmem/devices/foo/cells/bootdelay
> > > 5
> > >
> > > As you can see above NVMEM cells are not known at compilation time.
> >
> > Why do you want to expose these in a way that forces the kernel to parse
> > these key/value pairs? Why not just do it all in userspace like you can
> > today? What forces the kernel to do it and not a perl script?
> >
> > > So I believe the question is: how can I expose cells in sysfs?
> >
> > You can do this by dynamically creating the attributes on the fly, but
> > your show function is going to be rough and it's not going to be simple
> > to do so. One example will be the code that creates the
> > /sys/devices/system/machinecheck/machinecheckXX/bank* files.
> >
> > But I will push back again, why not just do it all in userspace? What
> > userspace tool is requiring the kernel to do this work for it?
>
> Environment data contains info that may be required by kernel.
>
> For example some home routers store two firmwares on flash. Kernel needs
> to read index of currently booted firmware to make sure MTD subsystem
> creates partitions correctly.
You are talking about a kernel<->kernel api here, that's not what sysfs
is for at all.
> Another example: MAC address. Ethernet subsystem supports reading MAC
> from NVMEM cell.
Again, internal kernel api, nothing sysfs is ever involved in.
> One could argue those tasks could be handled from userspace but that
> would get tricky. Sure - we have API for setting MAC address. However
> other cases (like setting active firmware partition and asking MTD to
> parse it into subpartitions) would require new user <-> kernel
> interfaces.
Ok, but again, sysfs is for userspace to get access to these values.
That's what I'm concerned about. If you want to make an in-kernel api
for other subsystems to get these key/value pairs, wonderful, that has
nothing to do with sysfs.
So I ask again, why do you want to expose these to userspace through
sysfs in a new format from what you have today. Who is going to use
that information and what is it going to be used for.
thanks,
greg k-h
next prev parent reply other threads:[~2021-12-21 15:02 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-12-20 6:47 [PATCH 1/2] sysfs: add sysfs_add_bin_file_to_group() Rafał Miłecki
2021-12-20 6:47 ` [PATCH 2/2] nvmem: expose NVMEM cells in sysfs Rafał Miłecki
2021-12-20 8:00 ` Greg Kroah-Hartman
2021-12-20 20:39 ` Rafał Miłecki
2021-12-21 6:33 ` Greg Kroah-Hartman
2021-12-21 6:39 ` Rafał Miłecki
2021-12-21 6:45 ` Greg Kroah-Hartman
2021-12-21 6:53 ` Rafał Miłecki
2021-12-21 7:13 ` Greg Kroah-Hartman
2021-12-21 12:24 ` Rafał Miłecki
2021-12-21 12:56 ` Greg Kroah-Hartman
2021-12-21 13:05 ` Rafał Miłecki
2021-12-21 13:27 ` Greg Kroah-Hartman
2021-12-21 13:52 ` Rafał Miłecki
2021-12-21 14:27 ` Greg Kroah-Hartman [this message]
2021-12-21 15:09 ` Rafał Miłecki
2021-12-21 15:18 ` Greg Kroah-Hartman
2021-12-21 15:33 ` Rafał Miłecki
2021-12-22 0:11 ` John Thomson
2021-12-20 8:01 ` [PATCH 1/2] sysfs: add sysfs_add_bin_file_to_group() Greg Kroah-Hartman
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=YcHkS0iDUhplbqUc@kroah.com \
--to=gregkh@linuxfoundation.org \
--cc=bhelgaas@google.com \
--cc=corbet@lwn.net \
--cc=dan.j.williams@intel.com \
--cc=daniel.vetter@ffwll.ch \
--cc=hkallweit1@gmail.com \
--cc=kw@linux.com \
--cc=linux-doc@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=rafael@kernel.org \
--cc=rafal@milecki.pl \
--cc=srinivas.kandagatla@linaro.org \
--cc=zajec5@gmail.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).