From mboxrd@z Thu Jan 1 00:00:00 1970 From: Kalle Valo Date: Sat, 06 Oct 2018 12:11:30 +0000 Subject: Re: [PATCH] wil6210: fix debugfs_simple_attr.cocci warnings Message-Id: <87pnwnff65.fsf@kamboji.qca.qualcomm.com> List-Id: References: <1538737646-118337-1-git-send-email-yuehaibing@huawei.com> <877eiw1wol.fsf@codeaurora.org> In-Reply-To: (Julia Lawall's message of "Fri, 5 Oct 2018 16:29:54 +0200 (CEST)") MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Julia Lawall Cc: YueHaibing , Maya Erez , linux-wireless@vger.kernel.org, wil6210@qti.qualcomm.com, kernel-janitors@vger.kernel.org, netdev@vger.kernel.org Julia Lawall writes: > On Fri, 5 Oct 2018, Kalle Valo wrote: > >> YueHaibing 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