Re: Cannot access force_remove sysfs

[YASUAKI ISHIMATSU <yasu.isimatu@gmail.com>]

Please ignore the e-mail.
I found a way to hot remove ACPI0004 device. If I found anything related to force_remove sysfs,
I'll let you know.

Thanks,
Yasuaki Ishimatsu

On 06/28/2017 02:16 PM, YASUAKI ISHIMATSU wrote:
> Our sever supports system board (defined as ACPI0004) hotplug. And to hot-remove the device safely,
> we control force_remove sysfs. But due to the following commit, ACPI0004 hotplug does not work.
> 
> commit ffc10d82ff5df7087a9b737de55a69ac4f89bf56
> Author: Michal Hocko <mhocko@suse.com>
> Date:   Mon Apr 3 09:40:23 2017 +0200
> 
>     ACPI / scan: Drop support for force_remove
> 
> ACPI0004 is defined as module device in ACPI specification. So we don't know what devices mounts on ACPI0004.
> So to hot-remove ACPI0004 safely, we implemented that ACPI004 can be hot removed only when acpi_force_hot_remove
> is set to 1 via force_remove sysfs. And if acpi_force_hot_remove is set to 0, kernel just notifies REMOVE request
> of ACPI0004 to udev so that user can offline the devices on ACPI0004 by udev rule.
> 
> In our udev script, we hot-removes ACPI0004 safely as follows:
> 
>   1. udev catches REMOVE request of a ACPI0004 and run our script
>   2. Our script offline all devices on the ACPI0004
>   3. Our script write 1 to force_remove sysfs so that ACPI0004 can be hot-removed.
>   4. Our script write 1 to eject sysfs of the ACPI0004 to hot remove ACPI0004
>   5. Our script write 0 to force_remove sysfs so that the ACPI0004 cannot be hot-removed.
> 
> But due to the commit ffc10d82ff5d, there is no way to hot remove ACPI0004.
> So please revert the commit.
> 
> Thanks,
> Yasuaki Ishimatsu
>