Support for ADS (Alternate Data Streams)

Support for ADS (Alternate Data Streams)

[cygwin]

While I recognize that ADS is not supported by POSIX, I was wondering
what if any support for ADS might exist within Cygwin.

The last time I looked into this was probably more than a decade ago
but I am seeing (unfortunately) more usage of ADS in the Windows
world, so I was wondering if there has been any effort to support in Cygwin?

Re: Support for ADS (Alternate Data Streams)

[Thomas Wolff]

Am 02.01.2022 um 21:50 schrieb cygwin@kosowsky.org:
> While I recognize that ADS is not supported by POSIX, I was wondering
> what if any support for ADS might exist within Cygwin.
>
> The last time I looked into this was probably more than a decade ago
> but I am seeing (unfortunately) more usage of ADS in the Windows
> world, so I was wondering if there has been any effort to support in Cygwin?
This was discussed in fact more than a decade ago:
https://sourceware.org/pipermail/cygwin/2009-November/181422.html

Re: Support for ADS (Alternate Data Streams)

[cygwin]

Yes I recall that thread :)
Indeed, I under the pseudonym (aputerguy) was the one who INITIATED
the thread :) [I own the domain kosowksy.org which my many
personalities share]
But looks like nothing was done since, right?

Thomas Wolff wrote at about 00:06:27 +0100 on Monday, January 3, 2022:
 > Am 02.01.2022 um 21:50 schrieb cygwin@kosowsky.org:
 > > While I recognize that ADS is not supported by POSIX, I was wondering
 > > what if any support for ADS might exist within Cygwin.
 > >
 > > The last time I looked into this was probably more than a decade ago
 > > but I am seeing (unfortunately) more usage of ADS in the Windows
 > > world, so I was wondering if there has been any effort to support in Cygwin?
 > This was discussed in fact more than a decade ago:
 > https://sourceware.org/pipermail/cygwin/2009-November/181422.html
 > 
 > -- 
 > Problem reports:      https://cygwin.com/problems.html
 > FAQ:                  https://cygwin.com/faq/
 > Documentation:        https://cygwin.com/docs.html
 > Unsubscribe info:     https://cygwin.com/ml/#unsubscribe-simple

Re: Support for ADS (Alternate Data Streams)

[NightStrike]

On Sun, Jan 2, 2022, 15:51 <cygwin@kosowsky.org> wrote:

> While I recognize that ADS is not supported by POSIX, I was wondering
> what if any support for ADS might exist within Cygwin.
>
> The last time I looked into this was probably more than a decade ago
> but I am seeing (unfortunately) more usage of ADS in the Windows
> world, so I was wondering if there has been any effort to support in
> Cygwin?
>
> --
> Problem reports:      https://cygwin.com/problems.html
> FAQ:                  https://cygwin.com/faq/
> Documentation:        https://cygwin.com/docs.html
> Unsubscribe info:     https://cygwin.com/ml/#unsubscribe-simple


FWIW, ntfs-3g under Linux maps these to extended attributes

Re: Support for ADS (Alternate Data Streams)

[Corinna Vinschen]

On Jan  3 22:40, NightStrike wrote:
> On Sun, Jan 2, 2022, 15:51 <cygwin@kosowsky.org> wrote:
> 
> > While I recognize that ADS is not supported by POSIX, I was wondering
> > what if any support for ADS might exist within Cygwin.
> >
> > The last time I looked into this was probably more than a decade ago
> > but I am seeing (unfortunately) more usage of ADS in the Windows
> > world, so I was wondering if there has been any effort to support in
> > Cygwin?
> >
> > --
> > Problem reports:      https://cygwin.com/problems.html
> > FAQ:                  https://cygwin.com/faq/
> > Documentation:        https://cygwin.com/docs.html
> > Unsubscribe info:     https://cygwin.com/ml/#unsubscribe-simple
> 
> 
> FWIW, ntfs-3g under Linux maps these to extended attributes

Using the EA API as ntfs-3g with the streams_interface=xattr option
seems like a nice way to allow reading and writing ADS on Cygwin as
well.

Do you know how ntfs-3g performs the mapping?  For instance, I guess
that ADS are stored in the user.* namespace?  Does listxattr list ADS or
does it skip them?  Stuff like that.


Corinna

Re: Support for ADS (Alternate Data Streams)

[NightStrike]

On Wed, Jan 5, 2022, 05:08 Corinna Vinschen <corinna-cygwin@cygwin.com>
wrote:

> On Jan  3 22:40, NightStrike wrote:
> > On Sun, Jan 2, 2022, 15:51 <cygwin@kosowsky.org> wrote:
> >
> > > While I recognize that ADS is not supported by POSIX, I was wondering
> > > what if any support for ADS might exist within Cygwin.
> > >
> > > The last time I looked into this was probably more than a decade ago
> > > but I am seeing (unfortunately) more usage of ADS in the Windows
> > > world, so I was wondering if there has been any effort to support in
> > > Cygwin?
> > >
> > > --
> > > Problem reports:      https://cygwin.com/problems.html
> > > FAQ:                  https://cygwin.com/faq/
> > > Documentation:        https://cygwin.com/docs.html
> > > Unsubscribe info:     https://cygwin.com/ml/#unsubscribe-simple
> >
> >
> > FWIW, ntfs-3g under Linux maps these to extended attributes
>
> Using the EA API as ntfs-3g with the streams_interface=xattr option
> seems like a nice way to allow reading and writing ADS on Cygwin as
> well.
>
> Do you know how ntfs-3g performs the mapping?  For instance, I guess
> that ADS are stored in the user.* namespace?  Does listxattr list ADS or
> does it skip them?  Stuff like that.
>

The ntfs.streams.list attribute contains the stream names, and there's a
shortcut to access them by name with a colon. So if you have a stream named
str and a file named f.txt, you could do 'cat f.txt:str'.

Re: Support for ADS (Alternate Data Streams)

[Corinna Vinschen]

On Jan  8 04:14, NightStrike wrote:
> On Wed, Jan 5, 2022, 05:08 Corinna Vinschen <corinna-cygwin@cygwin.com>
> wrote:
> 
> > On Jan  3 22:40, NightStrike wrote:
> > > On Sun, Jan 2, 2022, 15:51 <cygwin@kosowsky.org> wrote:
> > >
> > > > While I recognize that ADS is not supported by POSIX, I was wondering
> > > > what if any support for ADS might exist within Cygwin.
> > > >
> > > > The last time I looked into this was probably more than a decade ago
> > > > but I am seeing (unfortunately) more usage of ADS in the Windows
> > > > world, so I was wondering if there has been any effort to support in
> > > > Cygwin?
> > > >
> > > > --
> > > > Problem reports:      https://cygwin.com/problems.html
> > > > FAQ:                  https://cygwin.com/faq/
> > > > Documentation:        https://cygwin.com/docs.html
> > > > Unsubscribe info:     https://cygwin.com/ml/#unsubscribe-simple
> > >
> > >
> > > FWIW, ntfs-3g under Linux maps these to extended attributes
> >
> > Using the EA API as ntfs-3g with the streams_interface=xattr option
> > seems like a nice way to allow reading and writing ADS on Cygwin as
> > well.
> >
> > Do you know how ntfs-3g performs the mapping?  For instance, I guess
> > that ADS are stored in the user.* namespace?  Does listxattr list ADS or
> > does it skip them?  Stuff like that.
> >
> 
> The ntfs.streams.list attribute contains the stream names, and there's a
> shortcut to access them by name with a colon. So if you have a stream named
> str and a file named f.txt, you could do 'cat f.txt:str'.

Hmm, that's not quite what I expected.  We could support an EA like
ntfs.streams.list, but we can't use the colon syntax.

We could map streams to EAs so they are read with getxattr and written
with setxattr.  Or we would have to invent a different way.


Corinna