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. 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. Corinna
