Messages in this thread | | | Date | Thu, 9 Sep 2021 08:35:35 +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 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,
greg k-h
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