Re: [PATCH] sysfs: Remove page boundary align limitation on sysfs_emit and sysfs_emit_at

[Greg Kroah-Hartman]

On Thu, Sep 09, 2021 at 05:27:49AM +0000, Yu, Lang wrote:
> [AMD Official Use Only]
> 
> 
> 
> >-----Original Message-----
> >From: Joe Perches <joe@xxxxxxxxxxx>
> >Sent: Thursday, September 9, 2021 1:06 PM
> >To: Yu, Lang <Lang.Yu@xxxxxxx>; Greg Kroah-Hartman
> ><gregkh@xxxxxxxxxxxxxxxxxxx>; Rafael J . Wysocki <rafael@xxxxxxxxxx>; linux-
> >kernel@xxxxxxxxxxxxxxx
> >Subject: Re: [PATCH] sysfs: Remove page boundary align limitation on sysfs_emit
> >and sysfs_emit_at
> >
> >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.
> 
> But you said that " - 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.
> 
> Some guys just try to replace scnprintf with sysfs_emit() or sysfs_emit_at() per above documents.

That is just fine in sysfs show() functions.

> But sprintf and sysfs_emit/sysfs_emit_at are not totally equivalent(e.g., page boundary align).

Which is good, it checks for more error conditions.

I fail to understand what problem you have had with this.  What sysfs
file was converted and had issues?

> 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? Thanks.

There is no "old api" here.  People used a wide variety of different
things in sysfs file show() functions, now you can just use a single
one.

thanks,

greg k-h