On Wed, Mar 26, 2025 at 12:30 PM Corinna Vinschen <corinna-cyg...@cygwin.com> wrote: > > On Mar 25 19:21, Lionel Cons wrote: > > On Tue, 25 Mar 2025 at 17:19, Thomas Wolff <t...@towo.net> wrote: > > > > > > [oops, used wrong Reply function] > > > > > > Am 24.03.2025 um 21:58 schrieb Corinna Vinschen: > > > > On Mar 24 21:42, Thomas Wolff wrote: > > > >> > > > >> Am 24.03.2025 um 17:08 schrieb Jeffrey Altman: > > > >>> On 3/24/2025 10:25 AM, Martin Wege via Cygwin wrote: > > > >>>> Hello, > > > >>>> > > > >>>> another wishlist entry (old one): > > > >>>> read/write NTFS alternate data streams via openat(O_XATTR) > > > >>> From my perspective as a filesystem developer, Extended Attributes > > > >>> and > > > >>> Alternate Data Streams are different concepts which I believe are > > > >>> inappropriate to mix. > > > >>> > > > >>> Filesystems can implement one, the other, both or neither. > > > >>> > > > >>> An Extended Attribute is a name:value pair that can be attached to an > > > >>> inode. The size of individual values and the sum of the value sizes > > > >>> are often quite constrained because they are stored in the inode > > > >>> metadata. Copying an inode is guaranteed to copy the Extended > > > >>> Attributes. > > > >>> > > > >>> Alternate Data Streams are typically represented as independent > > > >>> inodes. The Alternate Data Stream namespace can be represented by a > > > >>> directory inode referenced from the file inode. Each ADS inode might > > > >>> have their own Extended Attributes to go along with the data stream. > > > >>> ACLs on ADS inodes can also be independent of the ACL on the primary > > > >>> inode depending upon the implementation. > > > >>> > > > >>> Therefore, I am reluctant to see openat(O_XATTR) be used to access > > > >>> alternate data streams. > > > >>> > > > >>> Jeffrey Altman > > > >> Why not use the Windows syntax? > > > >> cat file.txt:ads.txt > > > >> etc. (Was this discussed before?) > > > >> Thomas > > > > The colon is a valid filename character in Cygwin, it will be converted > > > > to the UNICODE private use area: > > > > https://cygwin.com/cygwin-ug-net/using-specialnames.html#pathnames-specialchars > > > > > > > > Therefore you can't use the colon to specify streams. > > > > > > > > > > > > Corinna > > > OK, so what about a slash? Handling the base file like a directory for > > > access and listing... > > > > ResierFS tried that, and Linus Torvalds personally crushed John Reiser for > > that. > > > > bash has cd -@ dir and cd -@ file to go into a virtual O_XATTR dir, > > UNIX has /bin/runat to do the same > > In Cygwin, openat is just a frontend to open.
Are you sure? Normally open() is a frontend to openat(), because openat(9 supports dir_fd, but open() does not. > I. e., if we support > openat(O_XATTR), we have to support open(O_XATTR) and define a way to > specify a colon in the filename so that it's not converted to the > UNICODE private use area. > > A preliminary change to the path handling code to disable encoding > the colon is necessary for that. > > With this pretty simple change, openat(fd, "bar", O_XATTR) should work > already, but openat(fd, ".", O_XATTR) or any other functionality won't. > > The latter is a big change. AFAICS it requires to add YA fhandler > overloading bunches of funtions per > https://docs.oracle.com/cd/E88353_01/html/E37853/fsattr-7.html > > Btw., does anybody know how to delete single streams? The > Sysinternals STreams command can do it, but as usual there's no > source code. open stream with "delete file" flag? Thanks, Martin
