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Subject: Re: [RFC PATCH 11/20] hfs: Explicitly set hsb->nls_disk when
 hsb->nls_io is set
From:   Viacheslav Dubeyko <slava@dubeyko.com>
In-Reply-To: <YRFnz6kn1UbSCN/S@casper.infradead.org>
Date:   Mon, 9 Aug 2021 11:00:29 -0700
Cc:     =?utf-8?Q?Pali_Roh=C3=A1r?= <pali@kernel.org>,
        Linux FS Devel <linux-fsdevel@vger.kernel.org>,
        linux-ntfs-dev@lists.sourceforge.net, linux-cifs@vger.kernel.org,
        jfs-discussion@lists.sourceforge.net,
        LKML <linux-kernel@vger.kernel.org>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Jan Kara <jack@suse.cz>,
        OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>,
        "Theodore Y . Ts'o" <tytso@mit.edu>,
        Luis de Bethencourt <luisbg@kernel.org>,
        Salah Triki <salah.triki@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Dave Kleikamp <shaggy@kernel.org>,
        Anton Altaparmakov <anton@tuxera.com>,
        Pavel Machek <pavel@ucw.cz>,
        =?utf-8?Q?Marek_Beh=C3=BAn?= <marek.behun@nic.cz>,
        Christoph Hellwig <hch@infradead.org>
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Message-Id: <E85E6FF7-AA14-4FA6-82AA-859D93BD0069@dubeyko.com>
References: <20210808162453.1653-1-pali@kernel.org>
 <20210808162453.1653-12-pali@kernel.org>
 <D0302F93-BAE5-48F0-87D0-B68B10D7757B@dubeyko.com>
 <YRFnz6kn1UbSCN/S@casper.infradead.org>
To:     Matthew Wilcox <willy@infradead.org>
Precedence: bulk


> On Aug 9, 2021, at 10:37 AM, Matthew Wilcox <willy@infradead.org> =
wrote:
>=20
> On Mon, Aug 09, 2021 at 10:31:55AM -0700, Viacheslav Dubeyko wrote:
>>> On Aug 8, 2021, at 9:24 AM, Pali Roh=C3=A1r <pali@kernel.org> wrote:
>>>=20
>>> 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.
>>>=20
>>> Reverse engineering driver code shown what is doing in this special =
case:
>>>=20
>>>   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".
>>>=20
>>> So when hsb->nls_disk is not set and hsb->nls_io is then explicitly =
set
>>> hsb->nls_disk to "iso8859-1".
>>>=20
>>> 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.
>>>=20
>>> 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.
>>=20
>>=20
>> Sounds reasonable. But it will be great to know that the change has =
been tested reasonably well.
>=20
> 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.

I see the point. But the whole approach needs to be tested as minimum =
for one particular file system. :) And it could be any favorite one.

Thanks,
Slava.