Hi Christoph.

[adding in Suzuki and Mathieu who maintain the coresight subsystem & lists]

You are correct - in this patchset we are adding the use of a binary attribute to load and unload Coresight configurations and features - which action has a side effect of adding and removing entries in particular sub-directories in our configfs sub-system.

Our use case for configfs is somewhat more complex than the other existing usages - such as ACPI, where the format of the directory structure and attributes is static, and known ahead of time.

The CoreSight configurations have variable numbers of attributes appearing in the configfs directories - so the attribute arrays are built dynamically at load time. The load process and also result in elements appearing in both the cs-syscfg/configurations and the cs-syscfg/features sub directories. This dynamic nature and split elements means that the traditional mkdir/rmdir configfs paradigm cannot be made to work.

We currently have two methods upstreamed for loading configurations, 1 is a configuration directly built into the coresight core code, and the other is to allow configurations to be loaded as kernel loadable modules. However these 2 are dependent on compile time operations, and have kernel dependencies.

Hence we have introduced the direct load via configfs binary attribute - which is more portable, flexible and convenient for the end user.

I appreciate that this may not be a usage you anticipated for configfs, but it does serve our purposes very well, and as far a I can tell from examination of configfs code and considerable testing, works fine and does not have any operational issues, other than the lockdep warnings on unload, which are caused be the fragment locks (lockdep being confused by holding the fragment for the initial cs-syscfg root system, and the one for the sub-directory we want to unload).

I am open to suggestions for a different way of doing this within the established directory structure we need to maintain.

Thanks and Regards

Mike

On Fri, 29 Jul 2022 at 14:24, Christoph Hellwig hch@lst.de wrote:

On Fri, Jul 29, 2022 at 07:41:00AM +0100, Mike Leach wrote:

...

Sure - see below

Happens during the unload process of the coresight configuration.

Hmm. It seems like youre bin_attr ->write handler (which gets called from configfs_release_bin_file) tries to unregister a group. That's not really how the configfs API is supposed to be used.

-- Mike Leach Principal Engineer, ARM Ltd. Manchester Design Centre. UK