Re: Making an interface for alternative data streams

["J. Bruce Fields" <bfields@fieldses.org>]

On Tue, Mar 22, 2016 at 01:13:49PM -0700, Richard Sharpe wrote:
> On Tue, Mar 22, 2016 at 1:08 PM, J. Bruce Fields <bfields@fieldses.org> wrote:
> > On Tue, Mar 22, 2016 at 09:15:44AM -0700, Richard Sharpe wrote:
> >> On Mon, Mar 21, 2016 at 7:21 PM, Richard Yao <ryao@gentoo.org> wrote:
> >> > On 03/21/2016 09:02 PM, Richard Yao wrote:
> >> >>
> >> >>> On Mar 21, 2016, at 8:12 PM, J. Bruce Fields <bfields@fieldses.org> wrote:
> >> >>>
> >> >>>> On Mon, Mar 21, 2016 at 11:48:04PM +0100, Cedric Blancher wrote:
> >> >>>> Old invalid argument, and Sophos and Symatec look there as well.
> >> >>>>
> >> >>>> If it was a bad idea, why has Linux fs attributes which are almost the
> >> >>>> same as O_XATTR except that they use a custom api? Why does Macos have
> >> >>>> alternate streams (called forks)? Why did Solaris adopt it long ago
> >> >>>> (and still gets support questions about it - just saying before
> >> >>>> someone argues that no one uses THAT)?
> >> >>>
> >> >>> Could you point us at some of those users?
> >> >>
> >> >> I am told that Samba users would love this functionality.
> >> >
> >> > Someone pinged me in IRC to let me know that Steve French was talking
> >> > about this earlier this month:
> >> >
> >> >> Have there been any suggestions on how to list alternate data streams
> >> >> on a file other than using a pseudo-xattr as ntfs-3g does (querying
> >> >> xattr ntfs.streams.list - see http://linux.die.net/man/8/ntfs-3g)?
> >> >
> >> > http://permalink.gmane.org/gmane.linux.kernel.cifs/11681
> >> >
> >> > Windows appears to have name-value pair attributes and alternative data
> >> > streams in separate name-spaces simultaneously.
> >>
> >> And it is more convoluted than that. If you use reparse points on a
> >> file you cannot use name-value pair attributes (Windows Extended
> >> Attributes) and vice versa, because they overloaded one of the fields
> >> use to report on those things.
> >>
> >> Of course, pretty much no one uses Windows Extended Attributes these
> >> days, I believe.
> >
> > But you do see people using "named attributes"/"alternative data
> > streams"?
> >
> > This comes up at the LSF/MM summit every now and then and Jeremy Allison
> > inevitably says "hah, only malware writers use those", and that's the
> > end of the discussion.  Sounds like Richard Yao has heard otherwise, but
> > it'd be nice to have actual examples of users.
> 
> I have worked on three products that run on UNIX (one on FreeBSD, two
> on Linux) that require Alternate Data Streams because customers demand
> them. In each case we used Samba and its streams_depot VFS module. The
> fact that Richard is discussing exposing streams in ZoL will be
> interesting to some users, possibly especially to those Taiwanese
> cheap NAS companies

Any clues on where we might look for example end users?  (So, not Samba,
or somebody else that's just passing along the interface, but an
application that's actually consuming it?)

> Named Attributes are pretty rare these days. I think that only virus
> checkers ever used them to store the fact that they had checked that
> file.

By the way, the language here cause me no end of confusion, because RFC
3530 (NFSv4) uses "named attributes" to mean alternate data streams.  So
I've tended to use "named" vs "extended" attributes to distinguish the
two cases, whereas you seem to use them as synonyms.

--b.