On 2020-03-13, Al Viro <viro@xxxxxxxxxxxxxxxxxx> wrote: > On Fri, Mar 13, 2020 at 08:59:01PM +1100, Aleksa Sarai wrote: > > On 2020-03-12, Stefan Metzmacher <metze@xxxxxxxxx> wrote: > > > Am 12.03.20 um 17:24 schrieb Linus Torvalds: > > > > But yes, if we have a major package like samba use it, then by all > > > > means let's add linkat2(). How many things are we talking about? We > > > > have a number of system calls that do *not* take flags, but do do > > > > pathname walking. I'm thinking things like "mkdirat()"?) > > > > > > I haven't looked them up in detail yet. > > > Jeremy can you provide a list? > > > > > > Do you think we could route some of them like mkdirat() and mknodat() > > > via openat2() instead of creating new syscalls? > > > > I have heard some folks asking for a way to create a directory and get a > > handle to it atomically -- so arguably this is something that could be > > inside openat2()'s feature set (O_MKDIR?). But I'm not sure how popular > > of an idea this is. > > For fuck sake, *NO*! > > We don't need any more multiplexors from hell. mkdir() and open() have > deeply different interpretation of pathnames (and anyone who asks for > e.g. traversals of dangling symlinks on mkdir() is insane). Don't try to > mix those; even O_TMPFILE had been a mistake. I agree that O_TMPFILE is a mess, and you're right that it wouldn't be a good idea to fold it into open*(). But what is your opinion on a hypothetical mkdirat2() which would let you get an fd to the directory that was just created? > We really don't need openat2() turning into another one. Syscall table > slots are not in a short supply, and the level of review one gets from > "new syscall added" is higher than from "make fubar(2) recognize a new > member in options->union_full_of_crap if it has RESOLVE_TO_WANK_WITH_RIGHT_HAND > set in options->flags, affecting its behaviour in some odd ways". > Which is a good thing, damnit. You're quite right, and I don't intend openat2() to become another ioctl-but-with-even-more-fun-semantics. -- Aleksa Sarai Senior Software Engineer (Containers) SUSE Linux GmbH <https://www.cyphar.com/>
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