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From: Steve French <smfrench@gmail.com>
Date: Wed, 23 Mar 2016 12:16:26 -0500
Message-ID: <CAH2r5mup-VexTcwdRpdm4WSaaiDR5XnH6KtZ5xohHO_hDso-9w@mail.gmail.com>
Subject: Re: Making an interface for alternative data streams
To: Jeremy Allison <jra@samba.org>
Cc: "J. Bruce Fields" <bfields@fieldses.org>,
        Richard Sharpe <realrichardsharpe@gmail.com>,
        Richard Yao <ryao@gentoo.org>,
        Cedric Blancher <cedric.blancher@gmail.com>,
        "Theodore Ts'o" <tytso@mit.edu>,
        Linux NFS Mailing List <linux-nfs@vger.kernel.org>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        Christoph Hellwig <hch@infradead.org>
Content-Type: text/plain; charset=UTF-8
Sender: linux-nfs-owner@vger.kernel.org

On Wed, Mar 23, 2016 at 12:01 PM, Jeremy Allison <jra@samba.org> wrote:
> On Wed, Mar 23, 2016 at 09:45:07AM -0500, Steve French wrote:
>> One of the arguments in favor of additional interfaces (ioctl or
>> openat) for accessing alternate data streams which may not be obvious
>> to Windows users is that while alternate data streams can be opened
>> just like regular files in Windows (and thus over SMB3 mounts), in
>> Linux it is hard to allow opening a stream and still support files
>> with the ':' (colon) character in their file name since colon is used
>> a separator for the stream name in Windows (and is a reserved
>> character), but is a valid character in POSIX.    When we use a cifs
>> or smb3 mount to Windows or Mac we typically map characters (into the
>> Unicode remap range just above 0xF000) like ':' the same way the Mac
>> does (and Windows services for Mac does as well).  This is enabled
>> with mount option "mapposix"
>>
>> So without an ioctl to query the stream contents (or a new syscall),
>> you have to choose whether to either allow : in a filename or allow
>> opening streams.
>>
>> There is some additional information on some of the more important
>> uses in Windows for alternate data streams at the end of the article
>> in this link: https://blogs.technet.microsoft.com/askcore/2013/03/24/alternate-data-streams-in-ntfs/
>
> Sorry Steve, but none of the uses in there can be called "important".
>
> I personally have an intense dislike for streams in a filesystem,
> and was very disappointed when Microsoft re-added them to the
> previously streamless ReFS (probably for backwards compatibility
> stuff like this).
>
> There's no way to transfer stream-riddled files over the Internet,
> and the amount of code complexity we have in Samba having to deal
> with them is nasty and has lead to more than one security hole in
> the past.
>
> Please don't add this to Linux.

Well, I can avoid setting them, but I do have to be able to query them
for backup.

-- 
Thanks,

Steve