On Sat, Aug 25, 2018 at 07:00:26PM +0100, Al Viro wrote: > > > Where do dentries of these things belong, anyway? > > > > Do streams have to have dentries? They don't have names in the hierarchy. > > Can they share their parent's dentry? Can they have a NULL dentry? Or > > a magic dentry of some kind? > > If you want them as opened files - yes, they have to, no, they can't and no, > they can't. I was hoping for something like alloc_file_pseudo() rather than having real dentries in the dentry tree. > > > > unlinkat() > > > > This is how you remove an individual named stream > > > > > > Yeah... and what happens to access via other hardlinks to the same parent > > > file? > > > > I'm not sure I understand the problem here. You have, say /a/b/c > > and /d which refer to the same inode. This inode has streams x and y. > > If you unlinkat() /a/b/c::x then it is no longer openable. Any currently > > existing open fds for x keep x alive until the last one is closed, no > > matter which path was used to open them. > > Again, where it the tree would the dentries live? And I really hope you are > not suggesting to reserve '::' - not when we have files like > /usr/share/man/man3/Params::Check.3perl.gz > just to pull a random line out of locate :: output here... I was just using '::' as shorthand for this email. Just to be clear, there's no intent to have these streams in the filesystem namespace. > > > > Unlinking a file with named streams removes all named streams from that > > > > file and then unlinks the file. Open streams will continue to exist in > > > > the filesystem until they are closed, just as unlinked files do. > > > > > > Can they be looked up by openat() from such a starting point? > > > > No, you can't use openat() on a stream fd. I should have been clearer > > on that above; this proposal should have split the syscall list in two; > > one for how the syscall behaves on a fd-for-a-file-with-streams and one > > for how the syscall behaves on a stream-fd. > > I'm not suggesting passing a stream fd as the starting point; just a normal > opened-and-then-unlinked regular file. Ah, I see your point. I think that it makes most sense to define the semantics of an open-but-unlinked file that you can create new streams, delete existing streams and rename streams until the last reference to that file are gone, and all references to streams within a file count as a reference on that file. Does that make sense? > > Right, but that code also assumes it's dealing with files. > > I'm looking forward to your analysis of all code related to dentry tree, > with an eye towards the places where such asserts are quietly made... I really was hoping not to change the dentry tree at all.
