On Fri, Mar 5, 2021 at 9:55 AM Greg KH [off-list ref] wrote:

On Fri, Mar 05, 2021 at 09:45:41AM +0100, Bartosz Golaszewski wrote:

quoted

On Fri, Mar 5, 2021 at 9:34 AM Greg KH [off-list ref] wrote:

quoted

On Fri, Mar 05, 2021 at 09:18:30AM +0100, Geert Uytterhoeven wrote:

quoted

CC Greg

On Thu, Mar 4, 2021 at 11:30 AM Bartosz Golaszewski [off-list ref] wrote:

quoted

From: Bartosz Golaszewski <redacted>

Export the symbol for device_is_bound() so that we can use it in gpio-sim
to check if the simulated GPIO chip is bound before fetching its driver
data from configfs callbacks in order to retrieve the name of the GPIO
chip device.

Signed-off-by: Bartosz Golaszewski <redacted>
---
 drivers/base/dd.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/base/dd.c b/drivers/base/dd.c
index 9179825ff646..c62c02e3490a 100644
--- a/drivers/base/dd.c
+++ b/drivers/base/dd.c

@@ -353,6 +353,7 @@ bool device_is_bound(struct device *dev)
 {
        return dev->p && klist_node_attached(&dev->p->knode_driver);
 }
+EXPORT_SYMBOL_GPL(device_is_bound);

No.  Please no.  Why is this needed?  Feels like someone is doing
something really wrong...

NACK.

I should have Cc'ed you the entire series, my bad.

This is the patch that uses this change - it's a new, improved testing
module for GPIO using configfs & sysfs as you (I think) suggested a
while ago:

https://lkml.org/lkml/2021/3/4/355

The story goes like this: committing the configfs item registers a
platform device.

Ick, no, stop there, that's not a "real" device, please do not abuse
platform devices like that, you all know I hate this :(

Use the virtbus code instead perhaps?

I have no idea what virtbus is and grepping for it only returns three
hits in: ./drivers/pci/iov.c and it's a function argument.

If it stands for virtual bus then for sure it sounds like the right
thing but I need to find more info on this.

quoted

As far as I understand - there's no guarantee that
the device will be bound to a driver before the commit callback (or
more specifically platform_device_register_full() in this case)
returns so the user may try to retrieve the name of the device
immediately (normally user-space should wait for the associated uevent
but nobody can force that) by doing:

mv /sys/kernel/config/gpio-sim/pending/foo /sys/kernel/config/gpio-sim/live/
cat /sys/kernel/config/gpio-sim/live/foo/dev_name

If the device is not bound at this point, we'll have a crash in the
kernel as opposed to just returning -ENODEV.

How will the kernel crash?  What has created the dev_name sysfs file
before it is possible to be read from?  That feels like the root
problem.

It's not sysfs - it's in configfs. Each chip has a read-only configfs
attribute that returns the name of the device - I don't really have a
better idea to map the configfs items to devices that committing
creates.

quoted

Please advise on how to handle it without device_is_bound().

Please do not create sysfs files before they can be read from :)

Don't worry, I don't.

Bartosz