Re: readdir(3): behavior on descriptors with O_SEARCH

[Dmitry Selyutin <ghostman.sd@gmail.com>]

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Hi Rich,

thank you for the detailed answer!

> If a program is doing this then trying to fdopendir/readdir, it's a
> bug in the program. A directory opened with O_SEARCH is only usable
> for search (attempting to access a file/directory in that directory
> by name, using one of the *at functions) not for reading. Unix has
> always distinguished search (+x) and read (+r) permission for
> directories and O_SEARCH vs O_RDONLY is similar.
Well, that's probably the worst kind of bugs, since it was caused by
misinterpretation of the documentation.
That was written intentionally due to misunderstanding, so I really want to
clarify the situation here.
So does it mean that descriptors opened with O_SEARCH are usable only for
*at functions?
I've been under the impression that it's part of the O_PATH functionality,
not O_SEARCH.

> It's been an ongoing fight even trying to get the kernel to reserve a
> bit number for them. It looks like the correct course of action (the
> one that's compatible with their non-action) is going to be using
> O_PATH|3 for both of them. This allows userspace open to process
> O_SEARCH and O_EXEC slightly differently from O_PATH (O_NOFOLLOW has
> different semantics) and the kernel will ignore the extra access mode
> bits with O_PATH anyway.
At the same time, if I understand you correctly, you mean that O_PATH is a
different beast than O_SEARCH.
I've found a mail in the DragonFly mailing list, which also slightly
touches this topic[0].
They also propose to use value 3 as currently unused value; I don't know if
it is implemented yet.
FWIW, neither OpenBSD nor FreeBSD provide O_SEARCH flag; the latter
provides O_EXEC though.

I finally have a good access to the Internet so I managed to find a
detailed discussion on this topic[1].
Sorry guys (and especially you, Rich) that I didn't find it before; it
would have saved some questions earlier.

Rich, could you please elaborate on the exact semantics of O_SEARCH flag?
Again, thank you very much for your answer and for your patience!


[0] https://www.dragonflybsd.org/mailarchive/kernel/2009-08/msg00000.html
[1] https://sourceware.org/ml/libc-alpha/2013-08/msg00016.html

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