[PATCH] nfsd as filesystem

* introduces a new filesystem - nfsd.  No, it's not a typo.  It's a small
  tree with fixed topology defined by nfsd and IO on its files does what
  we used to do by hand in nfsctl.c.
* turns sys_nfsservctl() into a sequence of open()/write()/read()/close()
  It works as it used to - we don't need nfsd to be mounted anywhere, etc.
* nfsd_linkage ugliness is gone.
* getfs and getfh demonstrate (rather trivial) example of "descriptor as
  transaction descriptor" behaviour.
* we are fairly close to the situation when driver-defined filesystems can
  be done with practically zero code overhead.  We are still not there, but
  it's a matter of adding a couple of helpers for populating the tree.

	One thing we get immediately is a cleanup of sys_nfsservctl() -
it got _much_ better.  Moreover, we get an alternative interface that
uses normal file IO and can be used without magic syscalls.

fs/Makefile

@@ -22,6 +22,12 @@ else
 obj-y += noquot.o
 endif
 
+ifneq ($(CONFIG_NFSD),n)
+ifneq ($(CONFIG_NFSD),)
+obj-y += nfsctl.o
+endif
+endif
+
 subdir-$(CONFIG_PROC_FS)	+= proc
 subdir-y			+= partitions
 subdir-y			+= driverfs

fs/dcache.c

@@ -1252,6 +1252,7 @@ kmem_cache_t *dquot_cachep;
 /* SLAB cache for buffer_head structures */
 kmem_cache_t *bh_cachep;
 EXPORT_SYMBOL(bh_cachep);
+EXPORT_SYMBOL(d_genocide);
 
 extern void bdev_cache_init(void);
 extern void cdev_cache_init(void);

fs/filesystems.c

@@ -3,39 +3,10 @@
  *
  *  Copyright (C) 1991, 1992  Linus Torvalds
  *
- *  nfsservctl system-call when nfsd is not compiled in.
+ *  table of configured filesystems
  */
 
-#include <linux/config.h>
-#include <linux/module.h>
-#include <linux/time.h>
-#include <linux/smp_lock.h>
-#include <linux/kmod.h>
-#include <linux/nfsd/interface.h>
-#include <linux/linkage.h>
-
-#if ! defined(CONFIG_NFSD)
-struct nfsd_linkage *nfsd_linkage;
-
-long
-asmlinkage sys_nfsservctl(int cmd, void *argp, void *resp)
-{
-	int ret = -ENOSYS;
-	
-#if defined(CONFIG_MODULES)
-	lock_kernel();
-
-	if (nfsd_linkage ||
-	    (request_module ("nfsd") == 0 && nfsd_linkage)) {
-		__MOD_INC_USE_COUNT(nfsd_linkage->owner);
-		unlock_kernel();
-		ret = nfsd_linkage->do_nfsservctl(cmd, argp, resp);
-		__MOD_DEC_USE_COUNT(nfsd_linkage->owner);
-	} else
-		unlock_kernel();
-#endif
-	return ret;
-}
-EXPORT_SYMBOL(nfsd_linkage);
-
-#endif /* CONFIG_NFSD */
+/*
+ * Code will move here from fs/super.c and yes, it will be fs type handling
+ * stuff.
+ */

fs/nfsctl.c

+/*
+ *	fs/nfsctl.c
+ *
+ *	This should eventually move to userland.
+ *
+ */
+#include <linux/config.h>
+#include <linux/file.h>
+#include <linux/fs.h>
+#include <linux/sunrpc/svc.h>
+#include <linux/nfsd/nfsd.h>
+#include <linux/nfsd/syscall.h>
+#include <linux/linkage.h>
+#include <asm/uaccess.h>
+
+/*
+ * open a file on nfsd fs
+ */
+
+struct vfsmount *do_kern_mount(const char *type, int flags, char *name, void *data);
+
+static struct file *do_open(char *name, int flags)
+{
+	struct nameidata nd;
+	int error;
+
+	nd.mnt = do_kern_mount("nfsd", 0, "nfsd", NULL);
+
+	if (IS_ERR(nd.mnt))
+		return (struct file *)nd.mnt;
+
+	nd.dentry = dget(nd.mnt->mnt_root);
+	nd.last_type = LAST_ROOT;
+	nd.flags = 0;
+
+	error = path_walk(name, &nd);
+	if (error)
+		return ERR_PTR(error);
+
+	return dentry_open(nd.dentry, nd.mnt, flags);
+}
+
+static struct {
+	char *name; int wsize; int rsize;
+} map[] = {
+	[NFSCTL_SVC]={"svc", sizeof(struct nfsctl_svc)},
+	[NFSCTL_ADDCLIENT]={"add", sizeof(struct nfsctl_client)},
+	[NFSCTL_DELCLIENT]={"del", sizeof(struct nfsctl_client)},
+	[NFSCTL_EXPORT]={"export", sizeof(struct nfsctl_export)},
+	[NFSCTL_UNEXPORT]={"unexport", sizeof(struct nfsctl_export)},
+#ifdef notyet
+	[NFSCTL_UGIDUPDATE]={"ugid", sizeof(struct nfsctl_uidmap)},
+#endif
+	[NFSCTL_GETFD]={"getfd", sizeof(struct nfsctl_fdparm), NFS_FHSIZE},
+	[NFSCTL_GETFS]={"getfs", sizeof(struct nfsctl_fsparm), sizeof(struct knfsd_fh)},
+};
+
+long
+asmlinkage sys_nfsservctl(int cmd, struct nfsctl_arg *arg, void *res)
+{
+	struct file *file;
+	void *p = &arg->u;
+	int version;
+	int err;
+
+	if (copy_from_user(&version, &arg->ca_version, sizeof(int)))
+		return -EFAULT;
+
+	if (version != NFSCTL_VERSION) {
+		printk(KERN_WARNING "nfsd: incompatible version in syscall.\n");
+		return -EINVAL;
+	}
+
+	if (cmd < 0 || cmd >= sizeof(map)/sizeof(map[0]) || !map[cmd].name)
+		return -EINVAL;
+
+	file = do_open(map[cmd].name, map[cmd].rsize ? O_RDWR : O_WRONLY);	
+	if (IS_ERR(file))
+		return PTR_ERR(file);
+	err = file->f_op->write(file, p, map[cmd].wsize, &file->f_pos);
+	if (err >= 0 && map[cmd].rsize)
+		err = file->f_op->read(file, res, map[cmd].rsize, &file->f_pos);
+	if (err >= 0)
+		err = 0;
+	fput(file);
+	return err;
+}

include/linux/nfsd/interface.h

@@ -10,17 +10,4 @@
 #ifndef LINUX_NFSD_INTERFACE_H
 #define LINUX_NFSD_INTERFACE_H
 
-#include <linux/config.h>
-
-#ifndef CONFIG_NFSD
-#ifdef CONFIG_MODULES
-
-extern struct nfsd_linkage {
-	long (*do_nfsservctl)(int cmd, void *argp, void *resp);
-	struct module *owner;
-} * nfsd_linkage;
-
-#endif
-#endif
-
 #endif /* LINUX_NFSD_INTERFACE_H */

include/linux/nfsd/syscall.h

@@ -133,7 +133,7 @@ union nfsctl_res {
  * Kernel syscall implementation.
  */
 #if defined(CONFIG_NFSD) || defined(CONFIG_NFSD_MODULE)
-extern asmlinkage long	sys_nfsservctl(int, void *, void *);
+extern asmlinkage long	sys_nfsservctl(int, struct nfsctl_arg *, void *);
 #else
 #define sys_nfsservctl		sys_ni_syscall
 #endif