On Mon, Jan 8, 2024 at 3:11 PM Corinna Vinschen via Cygwin <cygwin@cygwin.com> wrote: > > On Dec 18 18:47, Martin Wege via Cygwin wrote: > > On Fri, Dec 1, 2023 at 10:52 AM Corinna Vinschen via Cygwin > > <cygwin@cygwin.com> wrote: > > > > > > On Nov 30 04:55, Martin Wege via Cygwin wrote: > > > > Hello, > > > > > > > > Does Cygwin have tools (modified /usr/bin/dd ?) to read/write NTFS > > > > alternate data streams? > > > > > > No. As you know, the colon is translated to a normal filename > > > character, and there's no POSIX-like API to expose ADS raw to user > > > space. > > > > > > There is, however, an old function we still expose to user space > > > for backward compat: > > > > > > #include <sys/cygwin.h> > > > > > > int cygwin_attach_handle_to_fd (char *name, > > > int fd, > > > HANDLE handle, > > > mode_t bin, > > > DWORD myaccess); > > > > > > This allows to sneak in a HANDLE into a Cygwin file descriptor > > > representation, kind of like this: > > > > > > HANDLE h; > > > int fd; > > > > > > h = CreateFile ("foo:bar", GENERIC_READ, FILE_SHARE_VALID_FLAGS, > > > NULL, OPEN_EXISTING, 0, NULL); > > > if (h != INVALID_HANDLE_VALUE) > > > { > > > fd = cygwin_attach_handle_to_fd ("foo", -1, h, 0, GENERIC_READ); > > > if (fd < 0) > > > bail_out; > > > } > > > > > > For the bin parameter, only 0, O_BINARY or O_TEXT are acceptable, > > > for myaccess, only GENERIC_READ and/or GENERIC_WRITE are acceptable. > > > > Could this be abstracted into O_XATTR support, i.e. openat() file with > > O_XATTR, and then have access to the alternate data streams in a > > (virtual) subdir? > > I'm not too hot on adding more open(2) flags, the reason being, > that we have room left for only 7 more flags in the 32 bit mode. > Nobody knows what comes along officially in future.
Right, but Solaris, Illumos, and Opengroup draft already have O_XATTR, so this is IMO OK. Also, it would provide a good abstraction for alternate data stream support, which is compatible with Windows, OSX, Solaris, Illumos, and NTFS, ZFS, SMB, NFSv4. > > Apart from that, this sounds like a nice idea for Cygwin 3.6, > provided somebody implements it, https://cygwin.com/acronyms/#SHTDI > > Assuming we can live without actually having a subdir and just > allowing to open and create a file with the O_XATTR flag, it might be > pretty simple to implement. The path handling code would just have to > drop the colon from the list of characters converted to the private-use > Unicode area. > > Implementing the subdir is a bit more complicated, especially when > taking opendir/readdir of that virtual subdir into account, but it > would certainly be doable. How do other OSes implement the O_XATTR subdir? Thanks, Martin -- 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