On Sun, Sep 6, 2020 at 5:23 AM Juan José Santamaría Flecha <juanjo.santamaria@gmail.com> wrote: > On Sat, Sep 5, 2020 at 2:13 AM Andres Freund <andres@anarazel.de> wrote: >> > However, it looks like we might be missing a further opportunity >> > here... Doesn't Windows already give us the flags we need in the >> > dwFileAttributes member of the WIN32_FIND_DATA object that the >> > Find{First,Next}File() functions populate? >> >> That'd be better... > > > At first I did not see how to get DT_LNK directly, but it is possible without additional calls, so please find attached a version with that logic. > > This version also drops the enum, defining just the macros.
Excellent. I'd like to commit these soon, unless someone has a better idea for how to name file_utils_febe.c.
I think the following is a little mysterious, but it does seem to be what people do for this in other projects. It is the documented way to detect mount points, and I guess IO_REPARSE_TAG_MOUNT_POINT is either overloaded also for junctions, or junctions are the same thing as mount points. It would be nice to see a Win32 documentation page that explicitly said that.
The wikipedia page on it is actually fairly decent: https://en.wikipedia.org/wiki/NTFS_reparse_point. It's not the documentation of course, but it's easier to read :) The core difference is whether you mount a whole filesystem (mount point) or just a directory off something mounted elsehwere (junction).
And yes, the wikipedia page confirms that junctions also use IO_REPARSE_TAG_MOUNT_POINT.
+ /* For reparse points dwReserved0 field will contain the ReparseTag */ + else if ((fd.dwFileAttributes & FILE_ATTRIBUTE_REPARSE_POINT) != 0 + && (fd.dwReserved0 == IO_REPARSE_TAG_MOUNT_POINT)) + d->ret.d_type = DT_LNK;
Hmm, it's interesting that our existing test for a junction in pgwin32_is_junction() only looks for FILE_ATTRIBUTE_REPARSE_POINT and doesn't care what kind of reparse point it is.
I think that's mostly historical. When that code was written, the only two types of reparse points that existed were junctions and mount points -- which are as already noted, the same. Symbolic links, unix sockets and such things came later.