Messages in this thread | | | Date | Thu, 9 Sep 2021 09:59:58 +0200 | From | Greg Kroah-Hartman <> | Subject | Re: [PATCH] sysfs: Remove page boundary align limitation on sysfs_emit and sysfs_emit_at |
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On Thu, Sep 09, 2021 at 07:48:38AM +0000, Yu, Lang wrote: > [Public] > > > > >-----Original Message----- > >From: Greg Kroah-Hartman <gregkh@linuxfoundation.org> > >Sent: Thursday, September 9, 2021 2:36 PM > >To: Yu, Lang <Lang.Yu@amd.com> > >Cc: Joe Perches <joe@perches.com>; Rafael J . Wysocki <rafael@kernel.org>; > >linux-kernel@vger.kernel.org > >Subject: Re: [PATCH] sysfs: Remove page boundary align limitation on sysfs_emit > >and sysfs_emit_at > > > >On Thu, Sep 09, 2021 at 06:22:54AM +0000, Yu, Lang wrote: > >> [Public] > >> > >> > >> > >> >-----Original Message----- > >> >From: Greg Kroah-Hartman <gregkh@linuxfoundation.org> > >> >Sent: Thursday, September 9, 2021 2:08 PM > >> >To: Yu, Lang <Lang.Yu@amd.com> > >> >Cc: Joe Perches <joe@perches.com>; Rafael J . Wysocki > >> ><rafael@kernel.org>; linux-kernel@vger.kernel.org > >> >Subject: Re: [PATCH] sysfs: Remove page boundary align limitation on > >> >sysfs_emit and sysfs_emit_at > >> > > >> >On Thu, Sep 09, 2021 at 05:52:23AM +0000, Yu, Lang wrote: > >> >> [Public] > >> >> > >> >> > >> >> > >> >> >-----Original Message----- > >> >> >From: Joe Perches <joe@perches.com> > >> >> >Sent: Thursday, September 9, 2021 1:44 PM > >> >> >To: Yu, Lang <Lang.Yu@amd.com>; Greg Kroah-Hartman > >> >> ><gregkh@linuxfoundation.org>; Rafael J . Wysocki > >> >> ><rafael@kernel.org>; > >> >> >linux- kernel@vger.kernel.org > >> >> >Subject: Re: [PATCH] sysfs: Remove page boundary align limitation > >> >> >on sysfs_emit and sysfs_emit_at > >> >> > > >> >> >On Thu, 2021-09-09 at 05:27 +0000, Yu, Lang wrote: > >> >> >> [AMD Official Use Only] > >> >> > > >> >> >this is a public list and this marker is not appropriate. > >> >> > >> >> Sorry for that. > >> >> > > >> >> >> > -----Original Message----- > >> >> >> > From: Joe Perches <joe@perches.com> On Wed, 2021-09-08 at > >> >> >> > 20:07 > >> >> >> > +0800, Lang Yu wrote: > >> >> >> > > The key purpose of sysfs_emit and sysfs_emit_at is to ensure > >> >> >> > > that no overrun is done. Make them more equivalent with scnprintf. > >> >> >> > > >> >> >> > I can't think of a single reason to do this. > >> >> >> > sysfs_emit and sysfs_emit_at are specific to sysfs. > >> >> >> > > >> >> >> > Use of these functions outside of sysfs is not desired or supported. > >> >> >> > > >> >> >> Thanks for your reply. But I'm still curious why you put such a limitation. > >> >> >> As "Documentation/filesystems/sysfs.rst" described, we can just > >> >> >> use scnprintf(buf, PAGE_SIZE, "%s\n", dev->name) in show > >> >> >> functions without such a limitation. > >> >> > > >> >> >There's nothing particularly wrong with the use of scnprintf as above. > >> >> > > >> >> >The only real reason that sysfs_emit exists is to be able to > >> >> >reduce the kernel treewide quantity of uses of the sprintf family > >> >> >of functions that need to be analyzed for possible buffer overruns. > >> >> > > >> >> >The issue there is that buf is already known to be both a > >> >> >PAGE_SIZE buffer and PAGE_SIZE aligned for sysfs show functions so > >> >> >there's no real reason to use scnprintf. > >> >> > > >> >> >sysfs_emit is a shorter/smaller function and using it could avoid > >> >> >some sprintf defects. > >> >> > > >> >> >> Some guys just try to replace scnprintf with sysfs_emit() or > >> >> >> sysfs_emit_at() per > >> >> >above documents. > >> >> > > >> >> >So don't do that. > >> >> > > >> >> >> But sprintf and sysfs_emit/sysfs_emit_at are not totally > >> >> >> equivalent(e.g., page > >> >> >boundary align). > >> >> >> > >> >> >> In my opinion, we add a new api and try to replace an old api. > >> >> >> Does we need to make it more compatible with old api? > >> >> > > >> >> >IMO: no. > >> >> > > >> >> But why you said " - show() should only use sysfs_emit() or > >> >> sysfs_emit_at() when formatting the value to be returned to user > >> >> space. " in > >> >Documentation/filesystems/sysfs.rst ? > >> >> > >> >> Obviously, sysfs_emit() and sysfs_emit_at() can't cover all the > >> >> cases in show > >> >functions. > >> > > >> >Why not, what usage model can it not cover? > >> > >> Of course, we can modify driver code to obey sysfs_emit and sysfs_emit_at > >rules or just use scnprintf in show functions. > > > >Great, please do. > > > >> Now that you introduced them, why not make them more flexible like scnprintf > >family functions. > > > >Because that is not what they are for. > > > >> The page boundary align rule makes life hard and I don't like it : ). Many thanks > >for your explanations! > > > >Then fix your sysfs files to not violate the sysfs rules. > > > >Again, which files are having problems and need to be fixed? I will be glad to do > >this for you. > > Thanks. I can do it by myself instead of wasting your time... Many thanks!
When doing so, please switch to using DEVICE_ATTR_RO() instead of the "open coded" DEVICE_ATTR() usage in the driver. That way we all "know" that these are read-only attributes.
thanks,
greg k-h
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