linux-kernel - Re: [RFC PATCH v2 01/18] fat: Fix iocharset=utf8 mount option

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Date:   Tue, 10 Jan 2023 18:17:05 +0900
From:   OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
To:     Pali Rohár <pali@...nel.org>
Cc:     linux-fsdevel@...r.kernel.org,
        linux-ntfs-dev@...ts.sourceforge.net, linux-cifs@...r.kernel.org,
        jfs-discussion@...ts.sourceforge.net, linux-kernel@...r.kernel.org,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Jan Kara <jack@...e.cz>, "Theodore Y . Ts'o" <tytso@....edu>,
        Anton Altaparmakov <anton@...era.com>,
        Luis de Bethencourt <luisbg@...nel.org>,
        Salah Triki <salah.triki@...il.com>,
        Steve French <sfrench@...ba.org>, Paulo Alcantara <pc@....nz>,
        Ronnie Sahlberg <lsahlber@...hat.com>,
        Shyam Prasad N <sprasad@...rosoft.com>,
        Tom Talpey <tom@...pey.com>, Dave Kleikamp <shaggy@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Pavel Machek <pavel@....cz>,
        Christoph Hellwig <hch@...radead.org>,
        Kari Argillander <kari.argillander@...il.com>,
        Viacheslav Dubeyko <slava@...eyko.com>
Subject: Re: [RFC PATCH v2 01/18] fat: Fix iocharset=utf8 mount option

Pali Rohár <pali@...nel.org> writes:

> Currently iocharset=utf8 mount option is broken and error is printed to
> dmesg when it is used. To use UTF-8 as iocharset, it is required to use
> utf8=1 mount option.
>
> Fix iocharset=utf8 mount option to use be equivalent to the utf8=1 mount
> option and remove printing error from dmesg.

[...]

> -
> -	There is also an option of doing UTF-8 translations
> -	with the utf8 option.
> -
> -.. note:: ``iocharset=utf8`` is not recommended. If unsure, you should consider
> -	  the utf8 option instead.
> +	**utf8** is supported too and recommended to use.
>  
>  **utf8=<bool>**
> -	UTF-8 is the filesystem safe version of Unicode that
> -	is used by the console. It can be enabled or disabled
> -	for the filesystem with this option.
> -	If 'uni_xlate' gets set, UTF-8 gets disabled.
> -	By default, FAT_DEFAULT_UTF8 setting is used.
> +	Alias for ``iocharset=utf8`` mount option.
>  
>  **uni_xlate=<bool>**
>  	Translate unhandled Unicode characters to special
> diff --git a/fs/fat/Kconfig b/fs/fat/Kconfig
> index 238cc55f84c4..e98aaa3bb55b 100644
> --- a/fs/fat/Kconfig
> +++ b/fs/fat/Kconfig
> @@ -93,29 +93,12 @@ config FAT_DEFAULT_IOCHARSET
>  	  like FAT to use. It should probably match the character set
>  	  that most of your FAT filesystems use, and can be overridden
>  	  with the "iocharset" mount option for FAT filesystems.
> -	  Note that "utf8" is not recommended for FAT filesystems.
> -	  If unsure, you shouldn't set "utf8" here - select the next option
> -	  instead if you would like to use UTF-8 encoded file names by default.
> +	  "utf8" is supported too and recommended to use.

This patch fixes the issue of utf-8 partially only. I think we can't
still recommend only partially working one.

[...]

> -	opts->utf8 = IS_ENABLED(CONFIG_FAT_DEFAULT_UTF8) && is_vfat;
> -
>  	if (!options)
>  		goto out;
>  
> @@ -1318,10 +1316,14 @@ static int parse_options(struct super_block *sb, char *options, int is_vfat,
>  					| VFAT_SFN_CREATE_WIN95;
>  			break;
>  		case Opt_utf8_no:		/* 0 or no or false */
> -			opts->utf8 = 0;
> +			fat_reset_iocharset(opts);

This changes the behavior of "iocharset=iso8859-1,utf8=no" for
example. Do we need this user visible change here?

>  			break;
>  		case Opt_utf8_yes:		/* empty or 1 or yes or true */
> -			opts->utf8 = 1;
> +			fat_reset_iocharset(opts);
> +			iocharset = kstrdup("utf8", GFP_KERNEL);
> +			if (!iocharset)
> +				return -ENOMEM;
> +			opts->iocharset = iocharset;
>  			break;
>  		case Opt_uni_xl_no:		/* 0 or no or false */
>  			opts->unicode_xlate = 0;
> @@ -1359,18 +1361,11 @@ static int parse_options(struct super_block *sb, char *options, int is_vfat,
>  	}
>  
>  out:
> -	/* UTF-8 doesn't provide FAT semantics */
> -	if (!strcmp(opts->iocharset, "utf8")) {
> -		fat_msg(sb, KERN_WARNING, "utf8 is not a recommended IO charset"
> -		       " for FAT filesystems, filesystem will be "
> -		       "case sensitive!");
> -	}
> +	opts->utf8 = !strcmp(opts->iocharset, "utf8") && is_vfat;

Still broken, so I think we still need the warning here (would be
tweaked warning).

>  	/* If user doesn't specify allow_utime, it's initialized from dmask. */
>  	if (opts->allow_utime == (unsigned short)-1)
>  		opts->allow_utime = ~opts->fs_dmask & (S_IWGRP | S_IWOTH);
> -	if (opts->unicode_xlate)
> -		opts->utf8 = 0;

unicode_xlate option is exclusive with utf8, need to adjust
somewhere. (with this patch, unicode_xlate and utf8 will shows by
show_options())

> +	else if (utf8)
> +		return fat_utf8_strnicmp(name->name, str, alen);
> +	else
> +		return nls_strnicmp(t, name->name, str, alen);
>  }

Not strong opinion though, maybe we better to consolidate this to a
(inline) function? (FWIW, it may be better to refactor to provide some
filename functions to hide the detail of handling nls/utf8)

Thanks.
-- 
OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>