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Date:   Fri, 5 Oct 2018 16:29:54 +0200 (CEST)
From:   Julia Lawall <julia.lawall@lip6.fr>
To:     Kalle Valo <kvalo@codeaurora.org>
cc:     YueHaibing <yuehaibing@huawei.com>,
        Maya Erez <merez@codeaurora.org>,
        linux-wireless@vger.kernel.org, wil6210@qti.qualcomm.com,
        kernel-janitors@vger.kernel.org, netdev@vger.kernel.org
Subject: Re: [PATCH] wil6210: fix debugfs_simple_attr.cocci warnings
In-Reply-To: <877eiw1wol.fsf@codeaurora.org>
Message-ID: <alpine.DEB.2.20.1810051629140.3364@hadrien>
References: <1538737646-118337-1-git-send-email-yuehaibing@huawei.com> <877eiw1wol.fsf@codeaurora.org>
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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.

julia

>
> --
> Kalle Valo
>