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From:   Daeho Jeong <daeho43@gmail.com>
Date:   Thu, 9 Jul 2020 10:07:59 +0900
Message-ID: <CACOAw_zKK7oD+w2R-0OQGFvS5EUvWWTmyWvdTJZAqrLxHH1w5Q@mail.gmail.com>
Subject: Re: [PATCH v3] f2fs: add symbolic link to kobject in sysfs
To:     Greg KH <gregkh@linuxfoundation.org>
Cc:     linux-kernel@vger.kernel.org,
        linux-f2fs-devel@lists.sourceforge.net, kernel-team@android.com,
        Daeho Jeong <daehojeong@google.com>
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I thought it's working for our system. But as you said, it might be
not true for others. I got your point. Partition label would be a
great idea for us.

Thank you for your comment!

2020=EB=85=84 7=EC=9B=94 8=EC=9D=BC (=EC=88=98) =EC=98=A4=ED=9B=84 7:05, Gr=
eg KH <gregkh@linuxfoundation.org>=EB=8B=98=EC=9D=B4 =EC=9E=91=EC=84=B1:
>
> On Mon, Jul 06, 2020 at 08:47:07AM +0900, Daeho Jeong wrote:
> > > No Documentation/ABI/ entry for your new sysfs file/link?
> >
> > This is for adding a symbolic link to a pre-existed
> > /sys/fs/f2fs/<disk> directory and it means /sys/fs/f2fs/<mount> points
> > to /sys/fs/f2fs/<disk>. I already added the description of this in
> > Documentation/filesystems/f2fs.rst.
>
> Ok, but that's not the standard location for sysfs file documentation.
>
> > > And what does this help with?
> >
> > Some system daemons in Android access with the pre-defined sysfs entry
> > name in the json file. So whenever the project changes and the
> > partition layout is changed, we have to follow up the changes and
> > modify /sys/fs/f2fs/<disk> name in the json file accordingly.
>
> That's what partition names are for, you should never depend on a
> "random number".
>
> > This will help them access all the f2fs sysfs entries consistently
> > without requiring to know those changes.
>
> No, please use a partition name, that is the only way to always know you
> are mounting the correct partition.  You have created a random number
> here that might, or might not, change between boots depending on the
> order of the filesystem being mounted.  It is not persistant or
> deterministic at all, please do not treat it as such.
>
> > > If it's really needed, why don't we do this for all filesystem types?
> >
> > This is for the daemon to change the mode of only F2FS with the power
> > hint of Android.
>
> Again, the point is that a filesystem type is not unique, this, if
> really really needed, should be an attribute for ALL filesystem types,
> f2fs is not special here at all.
>
> Please do not rely on this number ever being the same across boots,
> because your code is such that you can not guarantee that.
>
> And again, if you really want to know the partition you are mounting
> really is the partition you think you are mounting, use the partition
> label name, that is what it is there for, and is why we have been
> relying on that for decades.  A new special per-filesystem-attribute
> that is semi-random is not the correct solution for the problem you are
> describing as far as I can determine.
>
> thanks,
>
> greg k-h