Re: [RFC PATCH 11/20] hfs: Explicitly set hsb->nls_disk when hsb->nls_io is set

From: Viacheslav Dubeyko <slava@dubeyko.com>
To: Matthew Wilcox <willy@infradead.org>
Cc: "Pali Rohár" <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>, "Marek Behún" <marek.behun@nic.cz>,
	"Christoph Hellwig" <hch@infradead.org>
Subject: Re: [RFC PATCH 11/20] hfs: Explicitly set hsb->nls_disk when hsb->nls_io is set
Date: Mon, 9 Aug 2021 11:00:29 -0700	[thread overview]
Message-ID: <E85E6FF7-AA14-4FA6-82AA-859D93BD0069@dubeyko.com> (raw)
In-Reply-To: <YRFnz6kn1UbSCN/S@casper.infradead.org>

> On Aug 9, 2021, at 10:37 AM, Matthew Wilcox <willy@infradead.org> 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@kernel.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.

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.