Messages in this thread | | | Date | Thu, 9 Sep 2021 08:07:44 +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 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?
thanks,
greg k-h
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