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Re: C11 threads ABI questions - enum values
- From: Rich Felker <dalias at libc dot org>
- To: Christoph Hellwig <hch at lst dot de>
- Cc: "Joseph S. Myers" <joseph at codesourcery dot com>, Roland McGrath <roland at hack dot frob dot com>, libc-alpha at sourceware dot org
- Date: Fri, 3 Oct 2014 15:49:32 -0400
- Subject: Re: C11 threads ABI questions - enum values
- Authentication-results: sourceware.org; auth=none
- References: <20141001211606 dot GN23797 at brightrain dot aerifal dot cx> <20141001213022 dot 798942C3AAD at topped-with-meat dot com> <20141002001720 dot GO23797 at brightrain dot aerifal dot cx> <20141002214229 dot 734B62C3A2F at topped-with-meat dot com> <20141002222958 dot GR23797 at brightrain dot aerifal dot cx> <Pine dot LNX dot 4 dot 64 dot 1410031038300 dot 26280 at digraph dot polyomino dot org dot uk> <20141003151917 dot GS23797 at brightrain dot aerifal dot cx> <Pine dot LNX dot 4 dot 64 dot 1410031527460 dot 14538 at digraph dot polyomino dot org dot uk> <20141003153248 dot GT23797 at brightrain dot aerifal dot cx> <20141003183910 dot GA8806 at lst dot de>
On Fri, Oct 03, 2014 at 08:39:10PM +0200, Christoph Hellwig wrote:
> On Fri, Oct 03, 2014 at 11:32:48AM -0400, Rich Felker wrote:
> > Indeed, they need to be reserved on the kernel side, and during the
> > discussion on linux-api, almost everybody seemed to be failing to
> > understand why this is needed... :(
>
> At least of O_SEARCH and O_EXEC I strongly disagreed with the idea that
> they should be implementated in userspace and still do.
I do to, but for now it's the only way possible on Linux. For instance
it seems to be impossible to implement the POSIX rule (at least as I
understand it) that, when using an O_SEARCH or O_EXEC fd, the status
of the +x mode bit at open-time, rather than at the time of the
operation, dictates success or failure. There are a few other corner
cases where you want O_PATH and O_SEARCH/O_EXEC to behave differently,
too: for example, O_PATH|O_NOFOLLOW should open the symlink, while
O_SEARCH|O_NOFOLLOW or O_EXEC|O_NOFOLLOW should fail if the target is
a symlink.
Rich