Jan Blunck wrote: > On Tue, Apr 20, Jamie Lokier wrote: > > > Miklos Szeredi wrote: > > > On Mon, 19 Apr 2010, Valerie Aurora wrote: > > > > I don't recall there being any technical reason not to look up the > > > > real inode number. I just wrote it that we because I was lazy. So I > > > > like returning the directory's d_ino better than a single magic > > > > number, but I'd at least like to try returning the real inode number > > > > too. > > > > > > Note, "struct dirent" doesn't have d_dev, so you really can't return > > > the "real" inode number, that's on a different filesystem and just a > > > random number in the context of the the readdir in question. > > > > Agree. Does this inappropriate inode number for the union mount's > > st_dev happen with stat() on the actual files too? That could be bad. > > No, for stat() you do a lookup and that is returning the correct > dentry/inode for the filesystem the name is on. Hmm. I smell potential confusion for some otherwise POSIX-friendly userspaces. When I open /path/to/foo, call fstat (st_dev=2, st_ino=5678), and then keep the file open, then later do a readdir which includes foo (dir.st_dev=1, d_ino=1234), I'm going to immediately assume a rename or unlink happened, close the file, abort streaming from it, refresh the GUI windows, refresh application caches for that name entry, etc. Because in the POSIX world I think open files have stable inode numbers (as long as they are open), and I don't think that an open file can have it's name's d_ino not match the inode number unless it's a mount point, which my program would know about. This plays into inotify, where you have to know if you are monitoring every directory that contains a link to a file, to know if you need to monitor the file itself directly instead. Now I think it's fair enough that a union mount doesn't play all the traditional rules :-) C'est la vie. This mismatch of (dir.st_dev,d_ino) and st_ino strongly resembles a file-bind-mount. Like bind mounts, it's quite annoying for programs that like to assume they've seen all of a file's links when they've seen i_nlink of them. Bind mounts can be detected by looking in /proc/mounts. st_dev changing doesn't work because it can be a binding of the same filesystem. How would I go about detecting when a union mount's directory entry has similar behaviour, without calling stat() on each entry? Is it just a matter of recognising a particular filesystem name in /proc/mounts, or something more? Thanks, -- Jamie -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
