Re: [PATCH] wil6210: fix debugfs_simple_attr.cocci warnings

Kalle Valo
2018-10-06T12:11:30Z

Julia Lawall <julia.lawall@lip6.fr> writes:

> On Fri, 5 Oct 2018, Kalle Valo wrote:
>
>> YueHaibing <yuehaibing@huawei.com> writes:
>>
>> > Use DEFINE_DEBUGFS_ATTRIBUTE rather than DEFINE_SIMPLE_ATTRIBUTE
>> > for debugfs files.
>> >
>> > Semantic patch information:
>> > Rationale: DEFINE_SIMPLE_ATTRIBUTE + debugfs_create_file()
>> > imposes some significant overhead as compared to
>> > DEFINE_DEBUGFS_ATTRIBUTE + debugfs_create_file_unsafe().
>> >
>> > Generated by: scripts/coccinelle/api/debugfs/debugfs_simple_attr.cocci
>>
>> Just out of curiosity, what kind of overhead are we talking about here?
>
> The log message on the commit introducing the semantic patch says the
> following:
>
> In order to protect against file removal races, debugfs files created via
> debugfs_create_file() now get wrapped by a struct file_operations at their
> opening.
>
> If the original struct file_operations are known to be safe against removal
> races by themselves already, the proxy creation may be bypassed by creating
> the files through debugfs_create_file_unsafe().
>
> In order to help debugfs users who use the common
> DEFINE_SIMPLE_ATTRIBUTE() + debugfs_create_file()
> idiom to transition to removal safe struct file_operations, the helper
> macro DEFINE_DEBUGFS_ATTRIBUTE() has been introduced.
>
> Thus, the preferred strategy is to use
> DEFINE_DEBUGFS_ATTRIBUTE() + debugfs_create_file_unsafe()
> now.

I admit that I didn't have time to investigate this is detail but I'm
still not understanding where is that "significant overhead" coming from
and how big of overhead are we talking about? I guess it has something
to do with full_proxy_open() vs open_proxy_open()?

Not that I'm against this patch, just curious when I see someone
claiming "significant overhead" which is not obvious for me.

--
Kalle Valo