Messages in this thread | | | From | Rasmus Villemoes <> | Subject | Re: [git pull] vfs.git part 2 | Date | Fri, 12 Jul 2013 16:30:45 +0000 |
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Al Viro <viro@ZenIV.linux.org.uk> writes:
> On Fri, Jul 12, 2013 at 12:02:45PM +0000, Rasmus Villemoes wrote: > >> But isn't the problem the case where dirname does not exist? I.e., the >> application has to make sure that "/some/where" exists and is a directory >> before open("/some/where", O_CREAT | O_TMPFILE | O_RDWR, 0666) can be >> relied upon to fail on kernels not recognizing O_TMPFILE, instead of >> just creating "where" in "/some". >> >> Just thinking out loud, and please tell me to shut up if it doesn't make >> sense: The documentation for O_DIRECTORY seems to imply that one could >> require O_DIRECTORY to be given when using O_TMPFILE. The "If pathname >> is not a directory, cause the open to fail" certainly seems to make >> sense when O_TMPFILE is used, and older kernels should complain when >> seeing the O_CREAT|O_DIRECTORY combination. It is a hack, though. > > They should, but they won't ;-/
I see; I should test before I post, but...
> It's the same problem - we do *not* validate the flags argument. > We'll get to do_last(), hit lookup_open(), which will create the > sucker and go to finish_open_created. Which is past the logics > checking for LOOKUP_DIRECTORY trying to return a non-directory and it > would've been too late to fail anyway - the file has already been > created. IOW, O_DIRECTORY is ignored when O_CREAT is present *and* > file didn't exist already. In that case we almost certainly can treat > that as a bug (i.e. start failing open() on O_CREAT | O_DIRECTORY in > all cases - I'd be _very_ surprised if somebody called open() with > such combination of flags), but that doesn't help with older > kernels...
... it seems that if one then omits O_CREAT, things work out ok, as long as one uses O_RDWR (which is the only sane thing to do with O_TMPFILE, I guess):
open("/tmp/test/dir", O_DIRECTORY | O_RDWR, 0666) -> -1; Is a directory open("/tmp/test/dir", O_DIRECTORY | O_RDONLY, 0666) -> 3; Success open("/tmp/test/file", O_DIRECTORY | O_RDWR, 0666) -> -1; Not a directory open("/tmp/test/link_to_file", O_DIRECTORY | O_RDWR, 0666) -> -1; Not a directory open("/tmp/test/link_to_nowhere", O_DIRECTORY | O_RDWR, 0666) -> -1; No such file or directory open("/tmp/test/link_to_dir", O_DIRECTORY | O_RDWR, 0666) -> -1; Is a directory open("/tmp/test/link_to_dir", O_DIRECTORY | O_RDONLY, 0666) -> 3; Success open("/tmp/test/link_to_dir", O_NOFOLLOW | O_DIRECTORY | O_RDWR, 0666) -> -1; Too many levels of symbolic links open("/tmp/test/link_to_dir", O_NOFOLLOW | O_DIRECTORY | O_RDONLY, 0666) -> -1; Too many levels of symbolic links
(The above flags are what an old kernel would effectively see with or without O_TMPFILE present, I suppose.)
How about simply making O_TMPFILE == O_DIRECTORY | O_RDWR | O_TMPFILE_INTERNAL, and letting the correct use be
open("/some/dir", O_TMPFILE) [with or without a mode argument]
Using O_DIRECTORY when we don't want to open a directory, and omitting O_CREAT when we do want to create something new, is somewhat counter-intuitive, but I think this would solve the problem with old kernels.
Rasmus
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