linux-kernel - Re: tmpfs support of xattrs?

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Date:	Sun, 26 Oct 2008 12:26:35 +0000 (GMT)
From:	Hugh Dickins <hugh@...itas.com>
To:	Rob MacKinnon <c4blem0nkey@...il.com>
cc:	Stephen Smalley <sds@...ho.nsa.gov>,
	Andreas Gruenbacher <agruen@...e.de>,
	linux-kernel@...r.kernel.org
Subject: Re: tmpfs support of xattrs?

On Sat, 25 Oct 2008, Rob MacKinnon wrote:

> The background: So during the initial configuration of a box I enabled
> the xattr flags for ext3 and options of xattr in coreutils, and at the
> time didn't realize that I'd hit a snag that would finally annoy me
> enough after a month of getting a non-fatal error messages from cp "cp:
> listing attributes of `/dev/null`: Invalid argument" to spend half a day
> researching the cause and a potential solution.
> 
> Setup: udev mounts a tmpfs to /dev then fills it with device nodes.
> Problem: the resulting tmpfs has no xattr support.
> Therefore: Tmpfs without xattrs, and coreutils  and everywhere else with
> xattr support, cp freaks.
> 
> Is there sometime in the forseable future when the tmpfs module will
> support for xattrs in the stable branch, or should I "holler at the
> maintainers of coreutils to fix their broken code in cp". Even better
> (and I like this option the most) a little of both?

I've not seen "cp: listing attributes of `/dev/null': Invalid argument"
messages (or.. do I have a dim recollection of them once upon a time?).
I would certainly get irritated by them if I did, and want to fix them.
I tried "cp /dev/null temp" on a few distros just now but not seen it.

I never paid much attention to xattrs myself, but my understanding was
that tmpfs has supported xattrs since 2.6.10: from 2.6.10 to 2.6.13
there was CONFIG_TMPFS_XATTR to enable it, then from 2.6.14 to 2.6.18
it was using generic security fallbacks, then from 2.6.19 onwards
using generic security fallbacks plus its own enabled by
CONFIG_TMPFS_POSIX_ACL.

There's probably various pieces of info we need from you: what distro?
what kernel? what coreutils? CONFIG_TMPFS_POSIX_ACL=y? CONFIG_SHMEM=y?
what does "attr -l /dev/null" say?

But I may well be missing the _right_ questions to ask: Cc'ed
Stephen who made the 2.6.14 changes and Andreas who made the
2.6.19 changes, they may jump to the answer immediately.

Hugh
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