linux-kernel - Re: [RFC PATCH 11/20] hfs: Explicitly set hsb->nls_disk when hsb->nls

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Message-ID: <20210809174741.4wont2drya3rvpsr@pali>
Date:   Mon, 9 Aug 2021 19:47:41 +0200
From:   Pali Rohár <pali@...nel.org>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Viacheslav Dubeyko <slava@...eyko.com>,
        Linux FS Devel <linux-fsdevel@...r.kernel.org>,
        linux-ntfs-dev@...ts.sourceforge.net, linux-cifs@...r.kernel.org,
        jfs-discussion@...ts.sourceforge.net,
        LKML <linux-kernel@...r.kernel.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Jan Kara <jack@...e.cz>,
        OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>,
        "Theodore Y . Ts'o" <tytso@....edu>,
        Luis de Bethencourt <luisbg@...nel.org>,
        Salah Triki <salah.triki@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Dave Kleikamp <shaggy@...nel.org>,
        Anton Altaparmakov <anton@...era.com>,
        Pavel Machek <pavel@....cz>,
        Marek Behún <marek.behun@....cz>,
        Christoph Hellwig <hch@...radead.org>
Subject: Re: [RFC PATCH 11/20] hfs: Explicitly set hsb->nls_disk when
 hsb->nls_io is set

On Monday 09 August 2021 18:37:19 Matthew Wilcox wrote:
> On Mon, Aug 09, 2021 at 10:31:55AM -0700, Viacheslav Dubeyko wrote:
> > > On Aug 8, 2021, at 9:24 AM, Pali Rohár <pali@...nel.org> wrote:
> > > 
> > > It does not make any sense to set hsb->nls_io (NLS iocharset used between
> > > VFS and hfs driver) when hsb->nls_disk (NLS codepage used between hfs
> > > driver and disk) is not set.
> > > 
> > > Reverse engineering driver code shown what is doing in this special case:
> > > 
> > >    When codepage was not defined but iocharset was then
> > >    hfs driver copied 8bit character from disk directly to
> > >    16bit unicode wchar_t type. Which means it did conversion
> > >    from Latin1 (ISO-8859-1) to Unicode because first 256
> > >    Unicode code points matches 8bit ISO-8859-1 codepage table.
> > >    So when iocharset was specified and codepage not, then
> > >    codepage used implicit value "iso8859-1".
> > > 
> > > So when hsb->nls_disk is not set and hsb->nls_io is then explicitly set
> > > hsb->nls_disk to "iso8859-1".
> > > 
> > > Such setup is obviously incompatible with Mac OS systems as they do not
> > > support iso8859-1 encoding for hfs. So print warning into dmesg about this
> > > fact.
> > > 
> > > After this change hsb->nls_disk is always set, so remove code paths for
> > > case when hsb->nls_disk was not set as they are not needed anymore.
> > 
> > 
> > Sounds reasonable. But it will be great to know that the change has been tested reasonably well.
> 
> I don't think it's reasonable to ask Pali to test every single filesystem.
> That's something the maintainer should do, as you're more likely to have
> the infrastructure already set up to do testing of your filesystem and
> be aware of fun corner cases and use cases than someone who's working
> across all filesystems.

This patch series is currently in RFC form, as stated in cover letter
mostly untested. So they are not in form for merging or detailed
reviewing. I just would like to know if this is the right direction with
filesystems and if I should continue with this my effort or not.
And I thought that sending RFC "incomplete" patches is better way than
just describing what to do and how...