Re: Streams support in Linux

From: Jeremy Allison <jra@samba.org>
To: "Theodore Y. Ts'o" <tytso@mit.edu>
Cc: Matthew Wilcox <willy@infradead.org>,
	linux-fsdevel@vger.kernel.org, Eric Biggers <ebiggers@kernel.org>,
	samba-technical@lists.samba.org, jra@samba.org
Subject: Re: Streams support in Linux
Date: Mon, 27 Aug 2018 09:33:10 -0700	[thread overview]
Message-ID: <20180827163310.GA217636@jra3> (raw)
In-Reply-To: <20180825162547.GA10619@thunk.org>

On Sat, Aug 25, 2018 at 12:25:47PM -0400, Theodore Y. Ts'o via samba-technical wrote:
> On Sat, Aug 25, 2018 at 06:51:07AM -0700, Matthew Wilcox wrote:
> > 
> > Let's go over the properties of a file stream:
> > 
> >  - It has no life independent of the file it's attached to; you can't move
> >    it from one file to another
> >  - If the file is deleted, it is also deleted
> >  - If the file is renamed, it travels with the file
> >  - If the file is copied, the copying program decides whether any named
> >    streams are copied along with it.
> >  - Can be created, deleted.  Can be renamed?
> >  - Openable, seekable, cachable
> >  - Does not have sub-streams of its own
> >  - Directories may also have streams which are distinct from the files
> >    in the directory
> >  - Can pipes / sockets / device nodes / symlinks / ... have streams?  Unclear.
> >    Probably not useful.
> 
> Let's *not* make the mistakes Solaris did, and don't allow an fchdirat()
> into a streams directory.  Let's also not allow executing
> rootkits^H^H^H^H^H^H^H^H binaries as a stream.   :-)

After long and bitter experience with them, I have
come to the conclusion (aided greatly by Ted :-) that
streams are a *FUNDAMENTAL* mistake in filesystem
APIs and we should not have them implemented in
Linux.

I don't write the code, so don't get to chose
of course, but if I had to chose one essential
feature between file streams and RichACLs (which
are already supported for NFSv4) I would chose
RichACLs every time.

For anyone who is claiming that streams are essential
for Windows or Mac application compatibility I'd advise
them to take a look at the initial implementation of
Microsoft ReFS (which didn't support streams, might
do now) and Microsoft Azure SMB file server, which
*still* doesn't support named streams (although I'm
sure they're working on it):

https://docs.microsoft.com/en-us/rest/api/storageservices/features-not-supported-by-the-azure-file-service

Now tell me, if streams are so essential, how are
Microsoft getting *anyone* to migrate to Azure SMB
file service ?

Please let's not make the same mistake Windows NTFS
did here.

Jeremy.