From linux-kernel Wed Nov 07 00:12:24 2001 From: Nathan Scott Date: Wed, 07 Nov 2001 00:12:24 +0000 To: linux-kernel Subject: [RFC][PATCH] extended attributes X-MARC-Message: https://marc.info/?l=linux-kernel&m=100509197600341 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 */ - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/