linux-kernel - Re: [PATCH v2 2/4] Add fchmodat4(), a new syscall

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Message-ID: <20190717024046.GI1506@brightrain.aerifal.cx>
Date:   Tue, 16 Jul 2019 22:40:46 -0400
From:   Rich Felker <dalias@...c.org>
To:     Palmer Dabbelt <palmer@...ive.com>
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Subject: Re: [PATCH v2 2/4] Add fchmodat4(), a new syscall

On Tue, Jul 16, 2019 at 06:27:17PM -0700, Palmer Dabbelt wrote:
> man 3p says that fchmodat() takes a flags argument, but the Linux
> syscall does not.  There doesn't appear to be a good userspace
> workaround for this issue but the implementation in the kernel is pretty
> straight-forward.  The specific use case where the missing flags came up
> was WRT a fuse filesystem implemenation, but the functionality is pretty
> generic so I'm assuming there would be other use cases.

Note that we do have a workaround in musl libc with O_PATH and
/proc/self/fd, but a syscall that allows a proper fix with the ugly
workaround only in the fallback path for old kernels will be much
appreciated!

What about also doing a new SYS_faccessat4 with working AT_EACCESS
flag? The workaround we have to do for it is far worse.

Rich