On Mon, Mar 20, 2023 at 5:14 PM Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote: > > On Mon, Mar 20, 2023 at 4:52 AM Christian Brauner <brauner@xxxxxxxxxx> wrote: > > > > So before we continue down that road should we maybe treat this as a > > chance to fix the old bug? Because this behavior of returning -ENOTDIR > > has existed ever since v5.7 now. Since that time we had three LTS > > releases all returning ENOTDIR even if the file was created. > > Ack. > > I think considering that the return value has been broken for so long, > I think we can pretty much assume that there are no actual users of > it, and we might as well clean up the semantics properly. > > Willing to send that patch in and we'll get it tested in the crucible > of the real world? That sounds good to me, I can do that. What kind of new semantics are we talking about here? I originally found this when testing every kind of possibly-odd edge case in path walking/open(2). From the systems I've tested on (not too diverse, basically NetBSD, FreeBSD, Linux 6.2.2, and now, when looking for a regression, a variety of kernels since 2009), 4 behaviors occurred: 1) Pre v5.7 Linux did the open-dir-if-exists-else-create-regular-file we all know and """love""". 2) Post 5.7, we started returning this buggy -ENOTDIR error, even when successfully creating a file. 3) NetBSD just straight up returns EINVAL on open(O_DIRECTORY | O_CREAT) 4) FreeBSD's open(O_CREAT | O_DIRECTORY) succeeds if the file exists and is a directory. Fails with -ENOENT if it falls onto the "O_CREAT" path (i.e it doesn't try to create the file at all, just ENOENT's; this changed relatively recently, in 2015) Note that all of these behaviors are allowed by POSIX (in fact, I would not call the old Linux behavior a *bug*, just really odd semantics). So, again, what kind of behavior change do we want here? IMO, the best and least destructive would probably be to emulate FreeBSD behavior here. I don't think open(O_DIRECTORY | O_CREAT) returning -ENOTDIR if it doesn't exist (as Christian suggested, I think?) makes any sort of sense here. Just my 2c. -- Pedro
