NFSv4: Reduce the chances of an open_owner identifier collision

[mirror_ubuntu-artful-kernel.git] / fs / nfs / super.c

/*
 *  linux/fs/nfs/super.c
 *
 *  Copyright (C) 1992  Rick Sladkey
 *
 *  nfs superblock handling functions
 *
 *  Modularised by Alan Cox <Alan.Cox@linux.org>, while hacking some
 *  experimental NFS changes. Modularisation taken straight from SYS5 fs.
 *
 *  Change to nfs_read_super() to permit NFS mounts to multi-homed hosts.
 *  J.S.Peatfield@damtp.cam.ac.uk
 *
 *  Split from inode.c by David Howells <dhowells@redhat.com>
 *
 * - superblocks are indexed on server only - all inodes, dentries, etc. associated with a
 *   particular server are held in the same superblock
 * - NFS superblocks can have several effective roots to the dentry tree
 * - directory type roots are spliced into the tree when a path from one root reaches the root
 *   of another (see nfs_lookup())
 */

#include <linux/module.h>
#include <linux/init.h>

#include <linux/time.h>
#include <linux/kernel.h>
#include <linux/mm.h>
#include <linux/string.h>
#include <linux/stat.h>
#include <linux/errno.h>
#include <linux/unistd.h>
#include <linux/sunrpc/clnt.h>
#include <linux/sunrpc/stats.h>
#include <linux/sunrpc/metrics.h>
#include <linux/nfs_fs.h>
#include <linux/nfs_mount.h>
#include <linux/nfs4_mount.h>
#include <linux/lockd/bind.h>
#include <linux/smp_lock.h>
#include <linux/seq_file.h>
#include <linux/mount.h>
#include <linux/nfs_idmap.h>
#include <linux/vfs.h>
#include <linux/inet.h>
#include <linux/nfs_xdr.h>
#include <linux/magic.h>

#include <asm/system.h>
#include <asm/uaccess.h>

#include "nfs4_fs.h"
#include "callback.h"
#include "delegation.h"
#include "iostat.h"
#include "internal.h"

#define NFSDBG_FACILITY         NFSDBG_VFS

static void nfs_umount_begin(struct vfsmount *, int);
static int  nfs_statfs(struct dentry *, struct kstatfs *);
static int  nfs_show_options(struct seq_file *, struct vfsmount *);
static int  nfs_show_stats(struct seq_file *, struct vfsmount *);
static int nfs_get_sb(struct file_system_type *, int, const char *, void *, struct vfsmount *);
static int nfs_xdev_get_sb(struct file_system_type *fs_type,
                int flags, const char *dev_name, void *raw_data, struct vfsmount *mnt);
static void nfs_kill_super(struct super_block *);

static struct file_system_type nfs_fs_type = {
        .owner          = THIS_MODULE,
        .name           = "nfs",
        .get_sb         = nfs_get_sb,
        .kill_sb        = nfs_kill_super,
        .fs_flags       = FS_RENAME_DOES_D_MOVE|FS_REVAL_DOT|FS_BINARY_MOUNTDATA,
};

struct file_system_type nfs_xdev_fs_type = {
        .owner          = THIS_MODULE,
        .name           = "nfs",
        .get_sb         = nfs_xdev_get_sb,
        .kill_sb        = nfs_kill_super,
        .fs_flags       = FS_RENAME_DOES_D_MOVE|FS_REVAL_DOT|FS_BINARY_MOUNTDATA,
};

static const struct super_operations nfs_sops = {
        .alloc_inode    = nfs_alloc_inode,
        .destroy_inode  = nfs_destroy_inode,
        .write_inode    = nfs_write_inode,
        .statfs         = nfs_statfs,
        .clear_inode    = nfs_clear_inode,
        .umount_begin   = nfs_umount_begin,
        .show_options   = nfs_show_options,
        .show_stats     = nfs_show_stats,
};

#ifdef CONFIG_NFS_V4
static int nfs4_get_sb(struct file_system_type *fs_type,
        int flags, const char *dev_name, void *raw_data, struct vfsmount *mnt);
static int nfs4_xdev_get_sb(struct file_system_type *fs_type,
        int flags, const char *dev_name, void *raw_data, struct vfsmount *mnt);
static int nfs4_referral_get_sb(struct file_system_type *fs_type,
        int flags, const char *dev_name, void *raw_data, struct vfsmount *mnt);
static void nfs4_kill_super(struct super_block *sb);

static struct file_system_type nfs4_fs_type = {
        .owner          = THIS_MODULE,
        .name           = "nfs4",
        .get_sb         = nfs4_get_sb,
        .kill_sb        = nfs4_kill_super,
        .fs_flags       = FS_RENAME_DOES_D_MOVE|FS_REVAL_DOT|FS_BINARY_MOUNTDATA,
};

struct file_system_type nfs4_xdev_fs_type = {
        .owner          = THIS_MODULE,
        .name           = "nfs4",
        .get_sb         = nfs4_xdev_get_sb,
        .kill_sb        = nfs4_kill_super,
        .fs_flags       = FS_RENAME_DOES_D_MOVE|FS_REVAL_DOT|FS_BINARY_MOUNTDATA,
};

struct file_system_type nfs4_referral_fs_type = {
        .owner          = THIS_MODULE,
        .name           = "nfs4",
        .get_sb         = nfs4_referral_get_sb,
        .kill_sb        = nfs4_kill_super,
        .fs_flags       = FS_RENAME_DOES_D_MOVE|FS_REVAL_DOT|FS_BINARY_MOUNTDATA,
};

static const struct super_operations nfs4_sops = {
        .alloc_inode    = nfs_alloc_inode,
        .destroy_inode  = nfs_destroy_inode,
        .write_inode    = nfs_write_inode,
        .statfs         = nfs_statfs,
        .clear_inode    = nfs4_clear_inode,
        .umount_begin   = nfs_umount_begin,
        .show_options   = nfs_show_options,
        .show_stats     = nfs_show_stats,
};
#endif

static struct shrinker *acl_shrinker;

/*
 * Register the NFS filesystems
 */
int __init register_nfs_fs(void)
{
        int ret;

        ret = register_filesystem(&nfs_fs_type);
        if (ret < 0)
                goto error_0;

        ret = nfs_register_sysctl();
        if (ret < 0)
                goto error_1;
#ifdef CONFIG_NFS_V4
        ret = register_filesystem(&nfs4_fs_type);
        if (ret < 0)
                goto error_2;
#endif
        acl_shrinker = set_shrinker(DEFAULT_SEEKS, nfs_access_cache_shrinker);
        return 0;

#ifdef CONFIG_NFS_V4
error_2:
        nfs_unregister_sysctl();
#endif
error_1:
        unregister_filesystem(&nfs_fs_type);
error_0:
        return ret;
}

/*
 * Unregister the NFS filesystems
 */
void __exit unregister_nfs_fs(void)
{
        if (acl_shrinker != NULL)
                remove_shrinker(acl_shrinker);
#ifdef CONFIG_NFS_V4
        unregister_filesystem(&nfs4_fs_type);
        nfs_unregister_sysctl();
#endif
        unregister_filesystem(&nfs_fs_type);
}

/*
 * Deliver file system statistics to userspace
 */
static int nfs_statfs(struct dentry *dentry, struct kstatfs *buf)
{
        struct nfs_server *server = NFS_SB(dentry->d_sb);
        unsigned char blockbits;
        unsigned long blockres;
        struct nfs_fh *fh = NFS_FH(dentry->d_inode);
        struct nfs_fattr fattr;
        struct nfs_fsstat res = {
                        .fattr = &fattr,
        };
        int error;

        lock_kernel();

        error = server->nfs_client->rpc_ops->statfs(server, fh, &res);
        if (error < 0)
                goto out_err;
        buf->f_type = NFS_SUPER_MAGIC;

        /*
         * Current versions of glibc do not correctly handle the
         * case where f_frsize != f_bsize.  Eventually we want to
         * report the value of wtmult in this field.
         */
        buf->f_frsize = dentry->d_sb->s_blocksize;

        /*
         * On most *nix systems, f_blocks, f_bfree, and f_bavail
         * are reported in units of f_frsize.  Linux hasn't had
         * an f_frsize field in its statfs struct until recently,
         * thus historically Linux's sys_statfs reports these
         * fields in units of f_bsize.
         */
        buf->f_bsize = dentry->d_sb->s_blocksize;
        blockbits = dentry->d_sb->s_blocksize_bits;
        blockres = (1 << blockbits) - 1;
        buf->f_blocks = (res.tbytes + blockres) >> blockbits;
        buf->f_bfree = (res.fbytes + blockres) >> blockbits;
        buf->f_bavail = (res.abytes + blockres) >> blockbits;

        buf->f_files = res.tfiles;
        buf->f_ffree = res.afiles;

        buf->f_namelen = server->namelen;

        unlock_kernel();
        return 0;

 out_err:
        dprintk("%s: statfs error = %d\n", __FUNCTION__, -error);
        unlock_kernel();
        return error;
}

/*
 * Map the security flavour number to a name
 */
static const char *nfs_pseudoflavour_to_name(rpc_authflavor_t flavour)
{
        static const struct {
                rpc_authflavor_t flavour;
                const char *str;
        } sec_flavours[] = {
                { RPC_AUTH_NULL, "null" },
                { RPC_AUTH_UNIX, "sys" },
                { RPC_AUTH_GSS_KRB5, "krb5" },
                { RPC_AUTH_GSS_KRB5I, "krb5i" },
                { RPC_AUTH_GSS_KRB5P, "krb5p" },
                { RPC_AUTH_GSS_LKEY, "lkey" },
                { RPC_AUTH_GSS_LKEYI, "lkeyi" },
                { RPC_AUTH_GSS_LKEYP, "lkeyp" },
                { RPC_AUTH_GSS_SPKM, "spkm" },
                { RPC_AUTH_GSS_SPKMI, "spkmi" },
                { RPC_AUTH_GSS_SPKMP, "spkmp" },
                { -1, "unknown" }
        };
        int i;

        for (i=0; sec_flavours[i].flavour != -1; i++) {
                if (sec_flavours[i].flavour == flavour)
                        break;
        }
        return sec_flavours[i].str;
}

/*
 * Describe the mount options in force on this server representation
 */
static void nfs_show_mount_options(struct seq_file *m, struct nfs_server *nfss, int showdefaults)
{
        static const struct proc_nfs_info {
                int flag;
                const char *str;
                const char *nostr;
        } nfs_info[] = {
                { NFS_MOUNT_SOFT, ",soft", ",hard" },
                { NFS_MOUNT_INTR, ",intr", "" },
                { NFS_MOUNT_NOCTO, ",nocto", "" },
                { NFS_MOUNT_NOAC, ",noac", "" },
                { NFS_MOUNT_NONLM, ",nolock", "" },
                { NFS_MOUNT_NOACL, ",noacl", "" },
                { NFS_MOUNT_NORDIRPLUS, ",nordirplus", "" },
                { 0, NULL, NULL }
        };
        const struct proc_nfs_info *nfs_infop;
        struct nfs_client *clp = nfss->nfs_client;
        char buf[12];
        const char *proto;

        seq_printf(m, ",vers=%d", clp->rpc_ops->version);
        seq_printf(m, ",rsize=%d", nfss->rsize);
        seq_printf(m, ",wsize=%d", nfss->wsize);
        if (nfss->acregmin != 3*HZ || showdefaults)
                seq_printf(m, ",acregmin=%d", nfss->acregmin/HZ);
        if (nfss->acregmax != 60*HZ || showdefaults)
                seq_printf(m, ",acregmax=%d", nfss->acregmax/HZ);
        if (nfss->acdirmin != 30*HZ || showdefaults)
                seq_printf(m, ",acdirmin=%d", nfss->acdirmin/HZ);
        if (nfss->acdirmax != 60*HZ || showdefaults)
                seq_printf(m, ",acdirmax=%d", nfss->acdirmax/HZ);
        for (nfs_infop = nfs_info; nfs_infop->flag; nfs_infop++) {
                if (nfss->flags & nfs_infop->flag)
                        seq_puts(m, nfs_infop->str);
                else
                        seq_puts(m, nfs_infop->nostr);
        }
        switch (nfss->client->cl_xprt->prot) {
                case IPPROTO_TCP:
                        proto = "tcp";
                        break;
                case IPPROTO_UDP:
                        proto = "udp";
                        break;
                default:
                        snprintf(buf, sizeof(buf), "%u", nfss->client->cl_xprt->prot);
                        proto = buf;
        }
        seq_printf(m, ",proto=%s", proto);
        seq_printf(m, ",timeo=%lu", 10U * clp->retrans_timeo / HZ);
        seq_printf(m, ",retrans=%u", clp->retrans_count);
        seq_printf(m, ",sec=%s", nfs_pseudoflavour_to_name(nfss->client->cl_auth->au_flavor));
}

/*
 * Describe the mount options on this VFS mountpoint
 */
static int nfs_show_options(struct seq_file *m, struct vfsmount *mnt)
{
        struct nfs_server *nfss = NFS_SB(mnt->mnt_sb);

        nfs_show_mount_options(m, nfss, 0);

        seq_puts(m, ",addr=");
        seq_escape(m, nfss->nfs_client->cl_hostname, " \t\n\\");

        return 0;
}

/*
 * Present statistical information for this VFS mountpoint
 */
static int nfs_show_stats(struct seq_file *m, struct vfsmount *mnt)
{
        int i, cpu;
        struct nfs_server *nfss = NFS_SB(mnt->mnt_sb);
        struct rpc_auth *auth = nfss->client->cl_auth;
        struct nfs_iostats totals = { };

        seq_printf(m, "statvers=%s", NFS_IOSTAT_VERS);

        /*
         * Display all mount option settings
         */
        seq_printf(m, "\n\topts:\t");
        seq_puts(m, mnt->mnt_sb->s_flags & MS_RDONLY ? "ro" : "rw");
        seq_puts(m, mnt->mnt_sb->s_flags & MS_SYNCHRONOUS ? ",sync" : "");
        seq_puts(m, mnt->mnt_sb->s_flags & MS_NOATIME ? ",noatime" : "");
        seq_puts(m, mnt->mnt_sb->s_flags & MS_NODIRATIME ? ",nodiratime" : "");
        nfs_show_mount_options(m, nfss, 1);

        seq_printf(m, "\n\tage:\t%lu", (jiffies - nfss->mount_time) / HZ);

        seq_printf(m, "\n\tcaps:\t");
        seq_printf(m, "caps=0x%x", nfss->caps);
        seq_printf(m, ",wtmult=%d", nfss->wtmult);
        seq_printf(m, ",dtsize=%d", nfss->dtsize);
        seq_printf(m, ",bsize=%d", nfss->bsize);
        seq_printf(m, ",namelen=%d", nfss->namelen);

#ifdef CONFIG_NFS_V4
        if (nfss->nfs_client->cl_nfsversion == 4) {
                seq_printf(m, "\n\tnfsv4:\t");
                seq_printf(m, "bm0=0x%x", nfss->attr_bitmask[0]);
                seq_printf(m, ",bm1=0x%x", nfss->attr_bitmask[1]);
                seq_printf(m, ",acl=0x%x", nfss->acl_bitmask);
        }
#endif

        /*
         * Display security flavor in effect for this mount
         */
        seq_printf(m, "\n\tsec:\tflavor=%d", auth->au_ops->au_flavor);
        if (auth->au_flavor)
                seq_printf(m, ",pseudoflavor=%d", auth->au_flavor);

        /*
         * Display superblock I/O counters
         */
        for_each_possible_cpu(cpu) {
                struct nfs_iostats *stats;

                preempt_disable();
                stats = per_cpu_ptr(nfss->io_stats, cpu);

                for (i = 0; i < __NFSIOS_COUNTSMAX; i++)
                        totals.events[i] += stats->events[i];
                for (i = 0; i < __NFSIOS_BYTESMAX; i++)
                        totals.bytes[i] += stats->bytes[i];

                preempt_enable();
        }

        seq_printf(m, "\n\tevents:\t");
        for (i = 0; i < __NFSIOS_COUNTSMAX; i++)
                seq_printf(m, "%lu ", totals.events[i]);
        seq_printf(m, "\n\tbytes:\t");
        for (i = 0; i < __NFSIOS_BYTESMAX; i++)
                seq_printf(m, "%Lu ", totals.bytes[i]);
        seq_printf(m, "\n");

        rpc_print_iostats(m, nfss->client);

        return 0;
}

/*
 * Begin unmount by attempting to remove all automounted mountpoints we added
 * in response to xdev traversals and referrals
 */
static void nfs_umount_begin(struct vfsmount *vfsmnt, int flags)
{
        struct nfs_server *server = NFS_SB(vfsmnt->mnt_sb);
        struct rpc_clnt *rpc;

        shrink_submounts(vfsmnt, &nfs_automount_list);

        if (!(flags & MNT_FORCE))
                return;
        /* -EIO all pending I/O */
        rpc = server->client_acl;
        if (!IS_ERR(rpc))
                rpc_killall_tasks(rpc);
        rpc = server->client;
        if (!IS_ERR(rpc))
                rpc_killall_tasks(rpc);
}

/*
 * Validate the NFS2/NFS3 mount data
 * - fills in the mount root filehandle
 */
static int nfs_validate_mount_data(struct nfs_mount_data *data,
                                   struct nfs_fh *mntfh)
{
        if (data == NULL) {
                dprintk("%s: missing data argument\n", __FUNCTION__);
                return -EINVAL;
        }

        if (data->version <= 0 || data->version > NFS_MOUNT_VERSION) {
                dprintk("%s: bad mount version\n", __FUNCTION__);
                return -EINVAL;
        }

        switch (data->version) {
                case 1:
                        data->namlen = 0;
                case 2:
                        data->bsize  = 0;
                case 3:
                        if (data->flags & NFS_MOUNT_VER3) {
                                dprintk("%s: mount structure version %d does not support NFSv3\n",
                                                __FUNCTION__,
                                                data->version);
                                return -EINVAL;
                        }
                        data->root.size = NFS2_FHSIZE;
                        memcpy(data->root.data, data->old_root.data, NFS2_FHSIZE);
                case 4:
                        if (data->flags & NFS_MOUNT_SECFLAVOUR) {
                                dprintk("%s: mount structure version %d does not support strong security\n",
                                                __FUNCTION__,
                                                data->version);
                                return -EINVAL;
                        }
                case 5:
                        memset(data->context, 0, sizeof(data->context));
        }

        /* Set the pseudoflavor */
        if (!(data->flags & NFS_MOUNT_SECFLAVOUR))
                data->pseudoflavor = RPC_AUTH_UNIX;

#ifndef CONFIG_NFS_V3
        /* If NFSv3 is not compiled in, return -EPROTONOSUPPORT */
        if (data->flags & NFS_MOUNT_VER3) {
                dprintk("%s: NFSv3 not compiled into kernel\n", __FUNCTION__);
                return -EPROTONOSUPPORT;
        }
#endif /* CONFIG_NFS_V3 */

        /* We now require that the mount process passes the remote address */
        if (data->addr.sin_addr.s_addr == INADDR_ANY) {
                dprintk("%s: mount program didn't pass remote address!\n",
                        __FUNCTION__);
                return -EINVAL;
        }

        /* Prepare the root filehandle */
        if (data->flags & NFS_MOUNT_VER3)
                mntfh->size = data->root.size;
        else
                mntfh->size = NFS2_FHSIZE;

        if (mntfh->size > sizeof(mntfh->data)) {
                dprintk("%s: invalid root filehandle\n", __FUNCTION__);
                return -EINVAL;
        }

        memcpy(mntfh->data, data->root.data, mntfh->size);
        if (mntfh->size < sizeof(mntfh->data))
                memset(mntfh->data + mntfh->size, 0,
                       sizeof(mntfh->data) - mntfh->size);

        return 0;
}

/*
 * Initialise the common bits of the superblock
 */
static inline void nfs_initialise_sb(struct super_block *sb)
{
        struct nfs_server *server = NFS_SB(sb);

        sb->s_magic = NFS_SUPER_MAGIC;

        /* We probably want something more informative here */
        snprintf(sb->s_id, sizeof(sb->s_id),
                 "%x:%x", MAJOR(sb->s_dev), MINOR(sb->s_dev));

        if (sb->s_blocksize == 0)
                sb->s_blocksize = nfs_block_bits(server->wsize,
                                                 &sb->s_blocksize_bits);

        if (server->flags & NFS_MOUNT_NOAC)
                sb->s_flags |= MS_SYNCHRONOUS;

        nfs_super_set_maxbytes(sb, server->maxfilesize);
}

/*
 * Finish setting up an NFS2/3 superblock
 */
static void nfs_fill_super(struct super_block *sb, struct nfs_mount_data *data)
{
        struct nfs_server *server = NFS_SB(sb);

        sb->s_blocksize_bits = 0;
        sb->s_blocksize = 0;
        if (data->bsize)
                sb->s_blocksize = nfs_block_size(data->bsize, &sb->s_blocksize_bits);

        if (server->flags & NFS_MOUNT_VER3) {
                /* The VFS shouldn't apply the umask to mode bits. We will do
                 * so ourselves when necessary.
                 */
                sb->s_flags |= MS_POSIXACL;
                sb->s_time_gran = 1;
        }

        sb->s_op = &nfs_sops;
        nfs_initialise_sb(sb);
}

/*
 * Finish setting up a cloned NFS2/3 superblock
 */
static void nfs_clone_super(struct super_block *sb,
                            const struct super_block *old_sb)
{
        struct nfs_server *server = NFS_SB(sb);

        sb->s_blocksize_bits = old_sb->s_blocksize_bits;
        sb->s_blocksize = old_sb->s_blocksize;
        sb->s_maxbytes = old_sb->s_maxbytes;

        if (server->flags & NFS_MOUNT_VER3) {
                /* The VFS shouldn't apply the umask to mode bits. We will do
                 * so ourselves when necessary.
                 */
                sb->s_flags |= MS_POSIXACL;
                sb->s_time_gran = 1;
        }

        sb->s_op = old_sb->s_op;
        nfs_initialise_sb(sb);
}

static int nfs_set_super(struct super_block *s, void *_server)
{
        struct nfs_server *server = _server;
        int ret;

        s->s_fs_info = server;
        ret = set_anon_super(s, server);
        if (ret == 0)
                server->s_dev = s->s_dev;
        return ret;
}

static int nfs_compare_super(struct super_block *sb, void *data)
{
        struct nfs_server *server = data, *old = NFS_SB(sb);

        if (old->nfs_client != server->nfs_client)
                return 0;
        if (memcmp(&old->fsid, &server->fsid, sizeof(old->fsid)) != 0)
                return 0;
        return 1;
}

static int nfs_get_sb(struct file_system_type *fs_type,
        int flags, const char *dev_name, void *raw_data, struct vfsmount *mnt)
{
        struct nfs_server *server = NULL;
        struct super_block *s;
        struct nfs_fh mntfh;
        struct nfs_mount_data *data = raw_data;
        struct dentry *mntroot;
        int error;

        /* Validate the mount data */
        error = nfs_validate_mount_data(data, &mntfh);
        if (error < 0)
                return error;

        /* Get a volume representation */
        server = nfs_create_server(data, &mntfh);
        if (IS_ERR(server)) {
                error = PTR_ERR(server);
                goto out_err_noserver;
        }

        /* Get a superblock - note that we may end up sharing one that already exists */
        s = sget(fs_type, nfs_compare_super, nfs_set_super, server);
        if (IS_ERR(s)) {
                error = PTR_ERR(s);
                goto out_err_nosb;
        }

        if (s->s_fs_info != server) {
                nfs_free_server(server);
                server = NULL;
        }

        if (!s->s_root) {
                /* initial superblock/root creation */
                s->s_flags = flags;
                nfs_fill_super(s, data);
        }

        mntroot = nfs_get_root(s, &mntfh);
        if (IS_ERR(mntroot)) {
                error = PTR_ERR(mntroot);
                goto error_splat_super;
        }

        s->s_flags |= MS_ACTIVE;
        mnt->mnt_sb = s;
        mnt->mnt_root = mntroot;
        return 0;

out_err_nosb:
        nfs_free_server(server);
out_err_noserver:
        return error;

error_splat_super:
        up_write(&s->s_umount);
        deactivate_super(s);
        return error;
}

/*
 * Destroy an NFS2/3 superblock
 */
static void nfs_kill_super(struct super_block *s)
{
        struct nfs_server *server = NFS_SB(s);

        kill_anon_super(s);
        nfs_free_server(server);
}

/*
 * Clone an NFS2/3 server record on xdev traversal (FSID-change)
 */
static int nfs_xdev_get_sb(struct file_system_type *fs_type, int flags,
                           const char *dev_name, void *raw_data,
                           struct vfsmount *mnt)
{
        struct nfs_clone_mount *data = raw_data;
        struct super_block *s;
        struct nfs_server *server;
        struct dentry *mntroot;
        int error;

        dprintk("--> nfs_xdev_get_sb()\n");

        /* create a new volume representation */
        server = nfs_clone_server(NFS_SB(data->sb), data->fh, data->fattr);
        if (IS_ERR(server)) {
                error = PTR_ERR(server);
                goto out_err_noserver;
        }

        /* Get a superblock - note that we may end up sharing one that already exists */
        s = sget(&nfs_fs_type, nfs_compare_super, nfs_set_super, server);
        if (IS_ERR(s)) {
                error = PTR_ERR(s);
                goto out_err_nosb;
        }

        if (s->s_fs_info != server) {
                nfs_free_server(server);
                server = NULL;
        }

        if (!s->s_root) {
                /* initial superblock/root creation */
                s->s_flags = flags;
                nfs_clone_super(s, data->sb);
        }

        mntroot = nfs_get_root(s, data->fh);
        if (IS_ERR(mntroot)) {
                error = PTR_ERR(mntroot);
                goto error_splat_super;
        }

        s->s_flags |= MS_ACTIVE;
        mnt->mnt_sb = s;
        mnt->mnt_root = mntroot;

        dprintk("<-- nfs_xdev_get_sb() = 0\n");
        return 0;

out_err_nosb:
        nfs_free_server(server);
out_err_noserver:
        dprintk("<-- nfs_xdev_get_sb() = %d [error]\n", error);
        return error;

error_splat_super:
        up_write(&s->s_umount);
        deactivate_super(s);
        dprintk("<-- nfs_xdev_get_sb() = %d [splat]\n", error);
        return error;
}

#ifdef CONFIG_NFS_V4

/*
 * Finish setting up a cloned NFS4 superblock
 */
static void nfs4_clone_super(struct super_block *sb,
                            const struct super_block *old_sb)
{
        sb->s_blocksize_bits = old_sb->s_blocksize_bits;
        sb->s_blocksize = old_sb->s_blocksize;
        sb->s_maxbytes = old_sb->s_maxbytes;
        sb->s_time_gran = 1;
        sb->s_op = old_sb->s_op;
        nfs_initialise_sb(sb);
}

/*
 * Set up an NFS4 superblock
 */
static void nfs4_fill_super(struct super_block *sb)
{
        sb->s_time_gran = 1;
        sb->s_op = &nfs4_sops;
        nfs_initialise_sb(sb);
}

static void *nfs_copy_user_string(char *dst, struct nfs_string *src, int maxlen)
{
        void *p = NULL;

        if (!src->len)
                return ERR_PTR(-EINVAL);
        if (src->len < maxlen)
                maxlen = src->len;
        if (dst == NULL) {
                p = dst = kmalloc(maxlen + 1, GFP_KERNEL);
                if (p == NULL)
                        return ERR_PTR(-ENOMEM);
        }
        if (copy_from_user(dst, src->data, maxlen)) {
                kfree(p);
                return ERR_PTR(-EFAULT);
        }
        dst[maxlen] = '\0';
        return dst;
}

/*
 * Get the superblock for an NFS4 mountpoint
 */
static int nfs4_get_sb(struct file_system_type *fs_type,
        int flags, const char *dev_name, void *raw_data, struct vfsmount *mnt)
{
        struct nfs4_mount_data *data = raw_data;
        struct super_block *s;
        struct nfs_server *server;
        struct sockaddr_in addr;
        rpc_authflavor_t authflavour;
        struct nfs_fh mntfh;
        struct dentry *mntroot;
        char *mntpath = NULL, *hostname = NULL, ip_addr[16];
        void *p;
        int error;

        if (data == NULL) {
                dprintk("%s: missing data argument\n", __FUNCTION__);
                return -EINVAL;
        }
        if (data->version <= 0 || data->version > NFS4_MOUNT_VERSION) {
                dprintk("%s: bad mount version\n", __FUNCTION__);
                return -EINVAL;
        }

        /* We now require that the mount process passes the remote address */
        if (data->host_addrlen != sizeof(addr))
                return -EINVAL;

        if (copy_from_user(&addr, data->host_addr, sizeof(addr)))
                return -EFAULT;

        if (addr.sin_family != AF_INET ||
            addr.sin_addr.s_addr == INADDR_ANY
            ) {
                dprintk("%s: mount program didn't pass remote IP address!\n",
                                __FUNCTION__);
                return -EINVAL;
        }
        /* RFC3530: The default port for NFS is 2049 */
        if (addr.sin_port == 0)
                addr.sin_port = htons(NFS_PORT);

        /* Grab the authentication type */
        authflavour = RPC_AUTH_UNIX;
        if (data->auth_flavourlen != 0) {
                if (data->auth_flavourlen != 1) {
                        dprintk("%s: Invalid number of RPC auth flavours %d.\n",
                                        __FUNCTION__, data->auth_flavourlen);
                        error = -EINVAL;
                        goto out_err_noserver;
                }

                if (copy_from_user(&authflavour, data->auth_flavours,
                                   sizeof(authflavour))) {
                        error = -EFAULT;
                        goto out_err_noserver;
                }
        }

        p = nfs_copy_user_string(NULL, &data->hostname, 256);
        if (IS_ERR(p))
                goto out_err;
        hostname = p;

        p = nfs_copy_user_string(NULL, &data->mnt_path, 1024);
        if (IS_ERR(p))
                goto out_err;
        mntpath = p;

        dprintk("MNTPATH: %s\n", mntpath);

        p = nfs_copy_user_string(ip_addr, &data->client_addr,
                                 sizeof(ip_addr) - 1);
        if (IS_ERR(p))
                goto out_err;

        /* Get a volume representation */
        server = nfs4_create_server(data, hostname, &addr, mntpath, ip_addr,
                                    authflavour, &mntfh);
        if (IS_ERR(server)) {
                error = PTR_ERR(server);
                goto out_err_noserver;
        }

        /* Get a superblock - note that we may end up sharing one that already exists */
        s = sget(fs_type, nfs_compare_super, nfs_set_super, server);
        if (IS_ERR(s)) {
                error = PTR_ERR(s);
                goto out_free;
        }

        if (s->s_fs_info != server) {
                nfs_free_server(server);
                server = NULL;
        }

        if (!s->s_root) {
                /* initial superblock/root creation */
                s->s_flags = flags;
                nfs4_fill_super(s);
        }

        mntroot = nfs4_get_root(s, &mntfh);
        if (IS_ERR(mntroot)) {
                error = PTR_ERR(mntroot);
                goto error_splat_super;
        }

        s->s_flags |= MS_ACTIVE;
        mnt->mnt_sb = s;
        mnt->mnt_root = mntroot;
        kfree(mntpath);
        kfree(hostname);
        return 0;

out_err:
        error = PTR_ERR(p);
        goto out_err_noserver;

out_free:
        nfs_free_server(server);
out_err_noserver:
        kfree(mntpath);
        kfree(hostname);
        return error;

error_splat_super:
        up_write(&s->s_umount);
        deactivate_super(s);
        goto out_err_noserver;
}

static void nfs4_kill_super(struct super_block *sb)
{
        struct nfs_server *server = NFS_SB(sb);

        nfs_return_all_delegations(sb);
        kill_anon_super(sb);

        nfs4_renewd_prepare_shutdown(server);
        nfs_free_server(server);
}

/*
 * Clone an NFS4 server record on xdev traversal (FSID-change)
 */
static int nfs4_xdev_get_sb(struct file_system_type *fs_type, int flags,
                            const char *dev_name, void *raw_data,
                            struct vfsmount *mnt)
{
        struct nfs_clone_mount *data = raw_data;
        struct super_block *s;
        struct nfs_server *server;
        struct dentry *mntroot;
        int error;

        dprintk("--> nfs4_xdev_get_sb()\n");

        /* create a new volume representation */
        server = nfs_clone_server(NFS_SB(data->sb), data->fh, data->fattr);
        if (IS_ERR(server)) {
                error = PTR_ERR(server);
                goto out_err_noserver;
        }

        /* Get a superblock - note that we may end up sharing one that already exists */
        s = sget(&nfs_fs_type, nfs_compare_super, nfs_set_super, server);
        if (IS_ERR(s)) {
                error = PTR_ERR(s);
                goto out_err_nosb;
        }

        if (s->s_fs_info != server) {
                nfs_free_server(server);
                server = NULL;
        }

        if (!s->s_root) {
                /* initial superblock/root creation */
                s->s_flags = flags;
                nfs4_clone_super(s, data->sb);
        }

        mntroot = nfs4_get_root(s, data->fh);
        if (IS_ERR(mntroot)) {
                error = PTR_ERR(mntroot);
                goto error_splat_super;
        }

        s->s_flags |= MS_ACTIVE;
        mnt->mnt_sb = s;
        mnt->mnt_root = mntroot;

        dprintk("<-- nfs4_xdev_get_sb() = 0\n");
        return 0;

out_err_nosb:
        nfs_free_server(server);
out_err_noserver:
        dprintk("<-- nfs4_xdev_get_sb() = %d [error]\n", error);
        return error;

error_splat_super:
        up_write(&s->s_umount);
        deactivate_super(s);
        dprintk("<-- nfs4_xdev_get_sb() = %d [splat]\n", error);
        return error;
}

/*
 * Create an NFS4 server record on referral traversal
 */
static int nfs4_referral_get_sb(struct file_system_type *fs_type, int flags,
                                const char *dev_name, void *raw_data,
                                struct vfsmount *mnt)
{
        struct nfs_clone_mount *data = raw_data;
        struct super_block *s;
        struct nfs_server *server;
        struct dentry *mntroot;
        struct nfs_fh mntfh;
        int error;

        dprintk("--> nfs4_referral_get_sb()\n");

        /* create a new volume representation */
        server = nfs4_create_referral_server(data, &mntfh);
        if (IS_ERR(server)) {
                error = PTR_ERR(server);
                goto out_err_noserver;
        }

        /* Get a superblock - note that we may end up sharing one that already exists */
        s = sget(&nfs_fs_type, nfs_compare_super, nfs_set_super, server);
        if (IS_ERR(s)) {
                error = PTR_ERR(s);
                goto out_err_nosb;
        }

        if (s->s_fs_info != server) {
                nfs_free_server(server);
                server = NULL;
        }

        if (!s->s_root) {
                /* initial superblock/root creation */
                s->s_flags = flags;
                nfs4_fill_super(s);
        }

        mntroot = nfs4_get_root(s, &mntfh);
        if (IS_ERR(mntroot)) {
                error = PTR_ERR(mntroot);
                goto error_splat_super;
        }

        s->s_flags |= MS_ACTIVE;
        mnt->mnt_sb = s;
        mnt->mnt_root = mntroot;

        dprintk("<-- nfs4_referral_get_sb() = 0\n");
        return 0;

out_err_nosb:
        nfs_free_server(server);
out_err_noserver:
        dprintk("<-- nfs4_referral_get_sb() = %d [error]\n", error);
        return error;

error_splat_super:
        up_write(&s->s_umount);
        deactivate_super(s);
        dprintk("<-- nfs4_referral_get_sb() = %d [splat]\n", error);
        return error;
}

#endif /* CONFIG_NFS_V4 */