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Subject[RFC][PATCH] VFS interface for extended attributes
On Mon, Nov 12, 2001 at 02:20:29PM +1100, Nathan Scott wrote:
> On Mon, Nov 12, 2001 at 01:57:28AM +0000, Anton Altaparmakov wrote:
> > At 09:08 10/11/2001, Tim R. wrote:
> > >I'm glad to see you guys are working on a common acl api for ext2/3 and xfs.
> > >I was just wondering if this api provided what would be needed for linux
> > >to support NTFS's acls.
> >
> > Comments/problems for NTFS with proposed EA/ACL API:
> >
> > I think the API is good for extended attributes, no doubt. If we ever get
> > round to implementing EAs in NTFS then I would be happy to use the API. It
> > fully satisfies the needs of the NTFS EAs.
>
> That's great to hear! Thanks.
> ...
> I'll put out an initial attempt at some VFS code to sit behind
> this system call soon too.
>

Al, folks,

Andreas and I have been looking at several different VFS mechanisms
for extended attributes, I've included the code for one below, and
we're keen to get a bit of feedback here as well.

We started off with the simplest mechanism, just passing everything
straight down into the filesystem. I then played around with some
ways of separating out the different operations and then passing off
to the filesystem that way (see patch) to give the interface a more
rigid definition. Andreas' original mechanism was alot like this,
except used NULLs in some field values instead of explicit flags to
distinguish similar operations - that's another approach.

Yet another way would be to have an ea_operations vector separate to
the inode_operations with an ea_operations pointer in struct inode,
enumerating each EA operation and doing away with the flags (in the
patch below) altogether.

Any suggestions/improvements? The patch below is very much a work
in progress - it may even compile.

many thanks.

--
Nathan


diff -Naur 2.4.14-pristine/arch/i386/kernel/entry.S 2.4.14-explicit/arch/i386/kernel/entry.S
--- 2.4.14-pristine/arch/i386/kernel/entry.S Sat Nov 3 12:18:49 2001
+++ 2.4.14-explicit/arch/i386/kernel/entry.S Fri Nov 9 15:34:29 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_extattr)
+ .long SYMBOL_NAME(sys_lextattr)
+ .long SYMBOL_NAME(sys_fextattr)

.rept NR_syscalls-(.-sys_call_table)/4
.long SYMBOL_NAME(sys_ni_syscall)
diff -Naur 2.4.14-pristine/fs/Makefile 2.4.14-explicit/fs/Makefile
--- 2.4.14-pristine/fs/Makefile Tue Nov 6 08:40:59 2001
+++ 2.4.14-explicit/fs/Makefile Fri Nov 9 15:27:42 2001
@@ -14,7 +14,7 @@
super.o block_dev.o char_dev.o stat.o exec.o pipe.o namei.o \
fcntl.o ioctl.o readdir.o select.o fifo.o locks.o \
dcache.o inode.o attr.o bad_inode.o file.o iobuf.o dnotify.o \
- filesystems.o namespace.o
+ filesystems.o namespace.o extattr.o

ifeq ($(CONFIG_QUOTA),y)
obj-y += dquot.o
diff -Naur 2.4.14-pristine/fs/extattr.c 2.4.14-explicit/fs/extattr.c
--- 2.4.14-pristine/fs/extattr.c Thu Jan 1 10:00:00 1970
+++ 2.4.14-explicit/fs/extattr.c Mon Nov 12 11:24:11 2001
@@ -0,0 +1,101 @@
+/*
+ File: fs/extattr.c
+
+ Extended attribute handling.
+
+ Copyright (C) 2001 by Andreas Gruenbacher <a.gruenbacher@computer.org>
+ Copyright (C) 2001 SGI - Silicon Graphics, Inc <linux-xfs@oss.sgi.com>
+ */
+
+#include <linux/mm.h>
+#include <linux/fs.h>
+#include <linux/file.h>
+#include <linux/smp_lock.h>
+#include <linux/extattr.h>
+
+static long
+extattr_inode(struct inode *i, int cmd, char *name, void *value, size_t size)
+{
+ int error = -EOPNOTSUPP, flags = EA_FLAG_USER;
+
+ lock_kernel();
+ switch (cmd) {
+ case EA_SET:
+ case EA_CREATE:
+ case EA_REPLACE:
+ case EA_REMOVE:
+ if (!i->i_op->setxattr)
+ break;
+ if (cmd == EA_CREATE)
+ flags |= EA_FLAG_CREATE;
+ else if (cmd == EA_REPLACE)
+ flags |= EA_FLAG_REPLACE;
+ else if (cmd == EA_REMOVE)
+ flags |= EA_FLAG_REMOVE;
+ error = i->i_op->setxattr(i, name, value, size, flags);
+ break;
+
+ case EA_GETSIZE:
+ flags |= EA_FLAG_SZONLY;
+ case EA_GET:
+ if (!i->i_op->getxattr)
+ break;
+ error = i->i_op->getxattr(i, name, value, size, flags);
+ break;
+
+ case EA_LISTSIZE:
+ flags |= EA_FLAG_SZONLY;
+ case EA_LIST:
+ if (!i->i_op->listxattr)
+ break;
+ error = i->i_op->listxattr(i, name, value, size, flags);
+ break;
+
+ default:
+ error = -EINVAL;
+ }
+ unlock_kernel();
+ return error;
+}
+
+asmlinkage long
+sys_extattr(char *path, int cmd, char *name, void *value, size_t size)
+{
+ struct nameidata nd;
+ int error;
+
+ error = user_path_walk(path, &nd);
+ if (error)
+ return error;
+ error = extattr_inode(nd.dentry->d_inode, cmd, name, value, size);
+ path_release(&nd);
+ return error;
+}
+
+asmlinkage long
+sys_lextattr(char *path, int cmd, char *name, void *value, size_t size)
+{
+ struct nameidata nd;
+ int error;
+
+ error = user_path_walk_link(path, &nd);
+ if (error)
+ return error;
+ error = extattr_inode(nd.dentry->d_inode, cmd, name, value, size);
+ path_release(&nd);
+ return error;
+}
+
+asmlinkage long
+sys_fextattr(int fd, int cmd, char *name, void *value, size_t size)
+{
+ struct file *f;
+ int error = -EBADF;
+
+ f = fget(fd);
+ if (!f)
+ return error;
+ error = extattr_inode(f->f_dentry->d_inode, cmd, name, value, size);
+ fput(f);
+ return error;
+}
diff -Naur 2.4.14-pristine/include/asm-i386/unistd.h 2.4.14-explicit/include/asm-i386/unistd.h
--- 2.4.14-pristine/include/asm-i386/unistd.h Thu Oct 18 03:03:03 2001
+++ 2.4.14-explicit/include/asm-i386/unistd.h Fri Nov 9 15:37:08 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
+#define __NR_lextattr 227
+#define __NR_fextattr 228

/* user-visible error numbers are in the range -1 - -124: see <asm-i386/errno.h> */

diff -Naur 2.4.14-pristine/include/linux/extattr.h 2.4.14-explicit/include/linux/extattr.h
--- 2.4.14-pristine/include/linux/extattr.h Thu Jan 1 10:00:00 1970
+++ 2.4.14-explicit/include/linux/extattr.h Mon Nov 12 11:24:01 2001
@@ -0,0 +1,30 @@
+/*
+ File: linux/extattr.h
+
+ Extended attributes handling.
+
+ Copyright (C) 2001 by Andreas Gruenbacher <a.gruenbacher@computer.org>
+ Copyright (C) 2001 SGI - Silicon Graphics, Inc <linux-xfs@oss.sgi.com>
+*/
+#ifndef _LINUX_EXTATTR_H
+#define _LINUX_EXTATTR_H
+
+/* Operations */
+#define EA_SET 1 /* set the value, create attr where necessary */
+#define EA_CREATE 2 /* set the value, fail if attr already exists */
+#define EA_REPLACE 3 /* set the value, fail if attr does not exist */
+#define EA_REMOVE 4 /* remove the named attribute entirely */
+#define EA_GET 5 /* get the value for named attribute */
+#define EA_GETSIZE 6 /* size of value for named attribute */
+#define EA_LIST 7 /* get the list of attribute names */
+#define EA_LISTSIZE 8 /* size of list of attribute names */
+
+#ifdef __KERNEL__
+#define EA_FLAG_USER 0x0001
+#define EA_FLAG_SZONLY 0x0002
+#define EA_FLAG_CREATE 0x0004
+#define EA_FLAG_REPLACE 0x0008
+#define EA_FLAG_REMOVE 0x0010
+#endif
+
+#endif /* _LINUX_EXTATTR_H */
diff -Naur 2.4.14-pristine/include/linux/fs.h 2.4.14-explicit/include/linux/fs.h
--- 2.4.14-pristine/include/linux/fs.h Tue Nov 6 07:42:14 2001
+++ 2.4.14-explicit/include/linux/fs.h Sat Nov 10 14:10:39 2001
@@ -840,6 +840,9 @@
int (*revalidate) (struct dentry *);
int (*setattr) (struct dentry *, struct iattr *);
int (*getattr) (struct dentry *, struct iattr *);
+ int (*setxattr) (struct inode *, char *, void *, size_t, int);
+ int (*getxattr) (struct inode *, char *, void *, size_t, int);
+ int (*listxattr) (struct inode *, char *, void *, size_t, int);
};

/*
-
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