Cannot access force_remove sysfs

Cannot access force_remove sysfs

[YASUAKI ISHIMATSU]

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

Re: Cannot access force_remove sysfs

[YASUAKI ISHIMATSU]

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
>