Re: [PATCH 1/3] sysfs: Fix crash on empty group attributes array

[Lukas Wunner <lukas@wunner.de>]

On Sat, Apr 27, 2024 at 02:33:24PM -0700, Dan Williams wrote:
> Lukas Wunner wrote:
> > Perhaps an optional ->is_group_visible() callback in struct attribute_group
> > which gets passed only the struct kobject pointer?
> > 
> > At least for PCI device authentication, that would be sufficient.
> > I could get from the kobject to the corresponding struct device,
> > then determine whether the device supports authentication or not.
> > 
> > Because it's a new, optional callback, there should be no compatibility
> > issues.  The SYSFS_GROUP_INVISIBLE return code from the ->is_visible()
> > call for individual attributes would not be needed then, at least in my
> > use case.
> 
> That's where I started with this, but decided it was overkill to
> increase the size of that data structure globally for a small number of
> use cases.

Memory is cheap and memory-constrained devices can set CONFIG_SYSFS=n.

There aren't that many struct attribute_groups and this is just
8 additional bytes on a 64-bit machine.  (There are way more
struct attribute than struct attribute_group.)  The contortions
necessary to overload individual attribute ->is_visible() callbacks
to also govern the group's visibility aren't worth it.

Having an ->is_group_visible() callback has the additional benefit that
the mode of directories no longer needs to be hardcoded to 0755 in
sysfs_create_dir_ns(), but can be set to, say, 0500 or 0700 or 0511,
depending on the use case.  So more flexibility there as well.

Thanks,

Lukas