linux-kernel - Re: BUG? atleast >=2.6.19-rc5, x86 chroot on x86

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Date:	Tue, 05 Dec 2006 22:11:11 +0000
From:	David Howells <dhowells@...hat.com>
To:	Chuck Ebbert <76306.1226@...puserve.com>
Cc:	David Howells <dhowells@...hat.com>, vojtech@...e.cz, ak@....de,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Kasper Sandberg <lkml@...anurb.dk>,
	Andrew Morton <akpm@...l.org>
Subject: Re: BUG? atleast >=2.6.19-rc5, x86 chroot on x86_64 

Chuck Ebbert <76306.1226@...puserve.com> wrote:

> I only have 32-bit userspace.  When I run your program against
> a directory on a JFS filesystem (msdos ioctls not supported)
> I get this on vanilla 2.6.19:

Can I just check?  You're using an x86_64 CPU in 64-bit mode with a 64-bit
kernel, but with a completely 32-bit userspace?

> I only have 32-bit userspace.  When I run your program against
> a directory on a JFS filesystem (msdos ioctls not supported)
> I get this on vanilla 2.6.19:

Wait!  You're using JFS, not VFAT?  Oh... I see.

Okay: It's not the MSDOS/VFAT patch that's wrong.  Please don't revert that.
It's the compat ioctl code that's "wrong".

So compat_sys_ioctl() used to return ENOTTY (ENOIOCTLCMD internally) because
the MSDOS ioctl was listed as one that could be translated but it didn't apply
to JFS.

But now, since all the block-based filesystem ioctls have been removed from
that list, you now get EINVAL, not ENOTTY.

> So apparently this is a feature?

Unfortunately, I think it has to be.  We could add a master list of ioctls to
be issued with particular errors if the driver doesn't support them, but is it
worth it?

A question for you: Why is userspace assuming that it'll get ENOTTY rather
than EINVAL?

David
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