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Re: [Acl-Devel] Re: [RFC][PATCH] extended attributes

To: Nathan Scott <nathans@xxxxxxx>
Subject: Re: [Acl-Devel] Re: [RFC][PATCH] extended attributes
From: Stephen Tweedie <sct@xxxxxxxxxx>
Date: Thu, 8 Nov 2001 01:26:10 +0000
Cc: Andi Kleen <ak@xxxxxxx>, Linus Torvalds <torvalds@xxxxxxxxxxxxx>, Andreas Gruenbacher <ag@xxxxxxxxxxx>, linux-kernel@xxxxxxxxxxxxxxx, linux-fsdevel@xxxxxxxxxxxxxxx, acl-devel@xxxxxxxxxxx, linux-xfs@xxxxxxxxxxx
In-reply-to: <20011107141956.F591676@xxxxxxxxxxxxxxxxxxxxxxxx>; from nathans@xxxxxxx on Wed, Nov 07, 2001 at 02:19:56PM +1100
References: <20011107111224.C591676@xxxxxxxxxxxxxxxxxxxxxxxx> <20011107023218.A4754@xxxxxxxxxxxxx> <20011107141956.F591676@xxxxxxxxxxxxxxxxxxxxxxxx>
Sender: owner-linux-xfs@xxxxxxxxxxx
User-agent: Mutt/1.2.5i
Hi,

On Wed, Nov 07, 2001 at 02:19:56PM +1100, Nathan Scott wrote:
> On Wed, Nov 07, 2001 at 02:32:18AM +0100, Andi Kleen wrote:
> > EA_FIRST_ENTRY to reset the fd the first entry, EA_READ_ENTRY to 
> > read the next one.
> 
> I'm not sure this would work for the extattr/lextattr variants where
> we don't have an fd to hold the state.

> eg. the opening of the file before allowing a list operation could
> have implications for XFSs DMAPI support (open might recall data from
> tape),

There are other much more immediate obstacles: opening /dev/* is not
possible if the devices beneath the inodes don't exist.

O_OPENONLY (implying neither read nor write access) to get a stub file
handle for such inodes is possible, if a bit hackish.  There's a
problem in the kernel there --- kernel file descriptor operations on
"special" inodes such as named sockets/pipes or device nodes don't
pass file operations on to the underlying filesystem.  

As long as you're doing the ACL stuff via inode operations internally,
that's not a problem.  However, inode operations generally don't take
a file descriptor as an argument so you don't have access to the
cursor in that case.

The DMAPI and special inode problems go away if you don't demand a
file descriptor to the file.  (Having a file descriptor that
specifically belongs to the ACL stream is a different matter
entirely.)

--Stephen


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