Re: [RFC][PATCH] extended attributes

[Nathan Scott <nathans@sgi.com>]

Quick follow up - I had to botch _one_ of the CC'd lists I guess...
"linux-xfs@oss.sgi.comc" -> "linux-xfs@oss.sgi.com".  *sigh*

cheers.

On Wed, Nov 07, 2001 at 11:12:24AM +1100, Nathan Scott wrote:
> hi folks,
> 
> I've been discussing a filesystem extended attributes API with Andreas
> Gruenbacher (maintainer of the ext2/ext3 extended attributes patch[1])
> which is suitable for other Linux filesystems as well, in an effort to
> remove the differences between our current implementations and to help
> out the people building services layered above this (especially Samba).
> In doing so we have reviewed the earlier discussion[2,3] on this topic,
> and have attempted to produce a new interface which I believe satisfies
> many of the issues and ideas put forward there, while at the same time
> ensuring that the interface is simple, and remains true to the design
> of extended attributes being name:value pairs.
> 
> A manual page describing the system call interface can be found here[4].
> We're very interested in feedback on this.  In partiular, Linus - would
> you consider the patch below, which reserves system call numbers for
> this interface?  That would be a big help to our collaborative effort.
> 
> We have written most of the code for XFS, and Andreas is working away on
> the ext2/ext3 version.  Switching to a new syscall interface is going to
> cause several compatibility issues for our existing users, of course, so
> is not something we want to rush into before soliciting feedback and
> (hopefully) getting some system call numbers reserved - otherwise we may
> find ourselves needing to do a similar transition again later.
> 
> As a test case for the interface, we will now be able to use the same
> POSIX ACL userspace[1,5] between XFS and ext2 without any on-disk format
> changes in XFS - this was an important interface design goal for us XFS
> folk, where our format is fixed in stone as it is also used by IRIX.
> 
> We have also begun discussions with some of the LSM developers, with the
> goal of implementing POSIX capabilities and POSIX MAC (mandatory access
> control) security extensions in Linux also,  Here we again expect to be
> able to provide a filesystem independent view of these attributes, while
> still preserving the on-disk XFS format for these attributes using the
> simple namespace abstraction mechanism this new interface provides.
> 
> I've included some pointers[6,7,8,9,10] to other projects, developers,
> discussions, etc. which I've come across who are in some way or another
> interested in an extended attributes implementation in the base kernel
> - just as examples of how various people are using (or planning to use)
> the current ext2/ext3 and XFS interfaces on Linux.
> 
> cheers.
> 
> -- 
> Nathan
> 
> 
> [1] Extended attributes for ext2/ext3 and POSIX ACLs
>     http://acl.bestbits.at/
> [2] fs-devel extended attributes discussion
>     http://marc.theaimsgroup.com/?l=linux-fsdevel&m=97222475218787&w=2
> [3] Andrew Gildfind's interface comparison whitepaper
>     http://acl.bestbits.at/pre/gildfind-acls.pdf
> [4] New extattr(2) system call man pages
>     http://acl.bestbits.at/man/extattr.2.html
>     http://acl.bestbits.at/man/extattr.5.html
>     http://oss.sgi.com/cgi-bin/cvsweb.cgi/linux-2.4-xfs/cmd/attr2/man/man2/extattr.2
> [5] Common POSIX ACL implementation for Linux
>     http://acl.bestbits.at/pipermail/acl-devel/2001-February/000495.html
>     http://www.samba.org/samba/whatsnew/samba-2.2.0.html
> [6] Andrew Morgan's Filesystem Capability patches
>     http://www.kernel.org/pub/linux/libs/security/linux-privs/README
> [7] LSM - Linux Security Module project
>     http://www.linuxsecurity.com/articles/forums_article-2854.html
>     http://mail.wirex.com/pipermail/linux-security-module/2001-October/002310.html
> [8] DMAPI/XDSM specification - implemented in XFS via extended attributes
>     http://www.opengroup.org/onlinepubs/9657099/
>     http://oss.sgi.com/projects/xfs/dmapi.html
> [9] SnapFS snapshot filesystem
>     http://lwn.net/2001/0308/a/snapfs.php3
> [10] Will Dyson's resurrection of BeFS for Linux 2.4
>     http://cs.earlham.edu/~will/software/linux/kernel/BeFS.html
>     http://marc.theaimsgroup.com/?l=linux-fsdevel&m=100431033704112&w=2
> 
> 
> diff -Naur 2.4.14-pristine/arch/i386/kernel/entry.S 2.4.14-reserved/arch/i386/kernel/entry.S
> --- 2.4.14-pristine/arch/i386/kernel/entry.S	Sat Nov  3 12:18:49 2001
> +++ 2.4.14-reserved/arch/i386/kernel/entry.S	Wed Nov  7 10:02:59 2001
> @@ -622,6 +622,9 @@
>  	.long SYMBOL_NAME(sys_ni_syscall)	/* Reserved for Security */
>  	.long SYMBOL_NAME(sys_gettid)
>  	.long SYMBOL_NAME(sys_readahead)	/* 225 */
> +	.long SYMBOL_NAME(sys_ni_syscall)	/* reserved for extattr  */
> +	.long SYMBOL_NAME(sys_ni_syscall)	/* reserved for lextattr */
> +	.long SYMBOL_NAME(sys_ni_syscall)	/* reserved for fextattr */
>  
>  	.rept NR_syscalls-(.-sys_call_table)/4
>  		.long SYMBOL_NAME(sys_ni_syscall)
> diff -Naur 2.4.14-pristine/include/asm-i386/unistd.h 2.4.14-reserved/include/asm-i386/unistd.h
> --- 2.4.14-pristine/include/asm-i386/unistd.h	Thu Oct 18 03:03:03 2001
> +++ 2.4.14-reserved/include/asm-i386/unistd.h	Wed Nov  7 10:02:59 2001
> @@ -230,6 +230,9 @@
>  #define __NR_security		223	/* syscall for security modules */
>  #define __NR_gettid		224
>  #define __NR_readahead		225
> +#define __NR_extattr		226	/* syscall for extended attributes */
> +#define __NR_lextattr		227	/* syscall for extended attributes */
> +#define __NR_fextattr		228	/* syscall for extended attributes */
>  
>  /* user-visible error numbers are in the range -1 - -124: see <asm-i386/errno.h> */
>  
> -
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-- 
Nathan