Messages in this thread | | | From | "Yu, Lang" <> | Subject | RE: [PATCH] sysfs: Remove page boundary align limitation on sysfs_emit and sysfs_emit_at | Date | Thu, 9 Sep 2021 05:52:23 +0000 |
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[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.
Regards, Lang
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