drm/panthor: Don't add write fences to the shared BOs

[drm/drm-misc.git] / fs / nfsd / nfsfh.c

// SPDX-License-Identifier: GPL-2.0
/*
 * NFS server file handle treatment.
 *
 * Copyright (C) 1995, 1996 Olaf Kirch <okir@monad.swb.de>
 * Portions Copyright (C) 1999 G. Allen Morris III <gam3@acm.org>
 * Extensive rewrite by Neil Brown <neilb@cse.unsw.edu.au> Southern-Spring 1999
 * ... and again Southern-Winter 2001 to support export_operations
 */

#include <linux/exportfs.h>

#include <linux/sunrpc/svcauth_gss.h>
#include "nfsd.h"
#include "vfs.h"
#include "auth.h"
#include "trace.h"

#define NFSDDBG_FACILITY                NFSDDBG_FH


/*
 * our acceptability function.
 * if NOSUBTREECHECK, accept anything
 * if not, require that we can walk up to exp->ex_dentry
 * doing some checks on the 'x' bits
 */
static int nfsd_acceptable(void *expv, struct dentry *dentry)
{
        struct svc_export *exp = expv;
        int rv;
        struct dentry *tdentry;
        struct dentry *parent;

        if (exp->ex_flags & NFSEXP_NOSUBTREECHECK)
                return 1;

        tdentry = dget(dentry);
        while (tdentry != exp->ex_path.dentry && !IS_ROOT(tdentry)) {
                /* make sure parents give x permission to user */
                int err;
                parent = dget_parent(tdentry);
                err = inode_permission(&nop_mnt_idmap,
                                       d_inode(parent), MAY_EXEC);
                if (err < 0) {
                        dput(parent);
                        break;
                }
                dput(tdentry);
                tdentry = parent;
        }
        if (tdentry != exp->ex_path.dentry)
                dprintk("nfsd_acceptable failed at %p %pd\n", tdentry, tdentry);
        rv = (tdentry == exp->ex_path.dentry);
        dput(tdentry);
        return rv;
}

/* Type check. The correct error return for type mismatches does not seem to be
 * generally agreed upon. SunOS seems to use EISDIR if file isn't S_IFREG; a
 * comment in the NFSv3 spec says this is incorrect (implementation notes for
 * the write call).
 */
static inline __be32
nfsd_mode_check(struct dentry *dentry, umode_t requested)
{
        umode_t mode = d_inode(dentry)->i_mode & S_IFMT;

        if (requested == 0) /* the caller doesn't care */
                return nfs_ok;
        if (mode == requested) {
                if (mode == S_IFDIR && !d_can_lookup(dentry)) {
                        WARN_ON_ONCE(1);
                        return nfserr_notdir;
                }
                return nfs_ok;
        }
        if (mode == S_IFLNK) {
                if (requested == S_IFDIR)
                        return nfserr_symlink_not_dir;
                return nfserr_symlink;
        }
        if (requested == S_IFDIR)
                return nfserr_notdir;
        if (mode == S_IFDIR)
                return nfserr_isdir;
        return nfserr_wrong_type;
}

static bool nfsd_originating_port_ok(struct svc_rqst *rqstp,
                                     struct svc_cred *cred,
                                     struct svc_export *exp)
{
        if (nfsexp_flags(cred, exp) & NFSEXP_INSECURE_PORT)
                return true;
        /* We don't require gss requests to use low ports: */
        if (cred->cr_flavor >= RPC_AUTH_GSS)
                return true;
        return test_bit(RQ_SECURE, &rqstp->rq_flags);
}

static __be32 nfsd_setuser_and_check_port(struct svc_rqst *rqstp,
                                          struct svc_cred *cred,
                                          struct svc_export *exp)
{
        /* Check if the request originated from a secure port. */
        if (rqstp && !nfsd_originating_port_ok(rqstp, cred, exp)) {
                RPC_IFDEBUG(char buf[RPC_MAX_ADDRBUFLEN]);
                dprintk("nfsd: request from insecure port %s!\n",
                        svc_print_addr(rqstp, buf, sizeof(buf)));
                return nfserr_perm;
        }

        /* Set user creds for this exportpoint */
        return nfserrno(nfsd_setuser(cred, exp));
}

static inline __be32 check_pseudo_root(struct dentry *dentry,
                                       struct svc_export *exp)
{
        if (!(exp->ex_flags & NFSEXP_V4ROOT))
                return nfs_ok;
        /*
         * We're exposing only the directories and symlinks that have to be
         * traversed on the way to real exports:
         */
        if (unlikely(!d_is_dir(dentry) &&
                     !d_is_symlink(dentry)))
                return nfserr_stale;
        /*
         * A pseudoroot export gives permission to access only one
         * single directory; the kernel has to make another upcall
         * before granting access to anything else under it:
         */
        if (unlikely(dentry != exp->ex_path.dentry))
                return nfserr_stale;
        return nfs_ok;
}

/*
 * Use the given filehandle to look up the corresponding export and
 * dentry.  On success, the results are used to set fh_export and
 * fh_dentry.
 */
static __be32 nfsd_set_fh_dentry(struct svc_rqst *rqstp, struct net *net,
                                 struct svc_cred *cred,
                                 struct auth_domain *client,
                                 struct auth_domain *gssclient,
                                 struct svc_fh *fhp)
{
        struct knfsd_fh *fh = &fhp->fh_handle;
        struct fid *fid = NULL;
        struct svc_export *exp;
        struct dentry *dentry;
        int fileid_type;
        int data_left = fh->fh_size/4;
        int len;
        __be32 error;

        error = nfserr_badhandle;
        if (fh->fh_size == 0)
                return nfserr_nofilehandle;

        if (fh->fh_version != 1)
                return error;

        if (--data_left < 0)
                return error;
        if (fh->fh_auth_type != 0)
                return error;
        len = key_len(fh->fh_fsid_type) / 4;
        if (len == 0)
                return error;
        if (fh->fh_fsid_type == FSID_MAJOR_MINOR) {
                /* deprecated, convert to type 3 */
                len = key_len(FSID_ENCODE_DEV)/4;
                fh->fh_fsid_type = FSID_ENCODE_DEV;
                /*
                 * struct knfsd_fh uses host-endian fields, which are
                 * sometimes used to hold net-endian values. This
                 * confuses sparse, so we must use __force here to
                 * keep it from complaining.
                 */
                fh->fh_fsid[0] = new_encode_dev(MKDEV(ntohl((__force __be32)fh->fh_fsid[0]),
                                                      ntohl((__force __be32)fh->fh_fsid[1])));
                fh->fh_fsid[1] = fh->fh_fsid[2];
        }
        data_left -= len;
        if (data_left < 0)
                return error;
        exp = rqst_exp_find(rqstp ? &rqstp->rq_chandle : NULL,
                            net, client, gssclient,
                            fh->fh_fsid_type, fh->fh_fsid);
        fid = (struct fid *)(fh->fh_fsid + len);

        error = nfserr_stale;
        if (IS_ERR(exp)) {
                trace_nfsd_set_fh_dentry_badexport(rqstp, fhp, PTR_ERR(exp));

                if (PTR_ERR(exp) == -ENOENT)
                        return error;

                return nfserrno(PTR_ERR(exp));
        }

        if (exp->ex_flags & NFSEXP_NOSUBTREECHECK) {
                /* Elevate privileges so that the lack of 'r' or 'x'
                 * permission on some parent directory will
                 * not stop exportfs_decode_fh from being able
                 * to reconnect a directory into the dentry cache.
                 * The same problem can affect "SUBTREECHECK" exports,
                 * but as nfsd_acceptable depends on correct
                 * access control settings being in effect, we cannot
                 * fix that case easily.
                 */
                struct cred *new = prepare_creds();
                if (!new) {
                        error =  nfserrno(-ENOMEM);
                        goto out;
                }
                new->cap_effective =
                        cap_raise_nfsd_set(new->cap_effective,
                                           new->cap_permitted);
                put_cred(override_creds(new));
                put_cred(new);
        } else {
                error = nfsd_setuser_and_check_port(rqstp, cred, exp);
                if (error)
                        goto out;
        }

        /*
         * Look up the dentry using the NFS file handle.
         */
        error = nfserr_badhandle;

        fileid_type = fh->fh_fileid_type;

        if (fileid_type == FILEID_ROOT)
                dentry = dget(exp->ex_path.dentry);
        else {
                dentry = exportfs_decode_fh_raw(exp->ex_path.mnt, fid,
                                                data_left, fileid_type, 0,
                                                nfsd_acceptable, exp);
                if (IS_ERR_OR_NULL(dentry)) {
                        trace_nfsd_set_fh_dentry_badhandle(rqstp, fhp,
                                        dentry ?  PTR_ERR(dentry) : -ESTALE);
                        switch (PTR_ERR(dentry)) {
                        case -ENOMEM:
                        case -ETIMEDOUT:
                                break;
                        default:
                                dentry = ERR_PTR(-ESTALE);
                        }
                }
        }
        if (dentry == NULL)
                goto out;
        if (IS_ERR(dentry)) {
                if (PTR_ERR(dentry) != -EINVAL)
                        error = nfserrno(PTR_ERR(dentry));
                goto out;
        }

        if (d_is_dir(dentry) &&
                        (dentry->d_flags & DCACHE_DISCONNECTED)) {
                printk("nfsd: find_fh_dentry returned a DISCONNECTED directory: %pd2\n",
                                dentry);
        }

        fhp->fh_dentry = dentry;
        fhp->fh_export = exp;

        switch (fhp->fh_maxsize) {
        case NFS4_FHSIZE:
                if (dentry->d_sb->s_export_op->flags & EXPORT_OP_NOATOMIC_ATTR)
                        fhp->fh_no_atomic_attr = true;
                fhp->fh_64bit_cookies = true;
                break;
        case NFS3_FHSIZE:
                if (dentry->d_sb->s_export_op->flags & EXPORT_OP_NOWCC)
                        fhp->fh_no_wcc = true;
                fhp->fh_64bit_cookies = true;
                if (exp->ex_flags & NFSEXP_V4ROOT)
                        goto out;
                break;
        case NFS_FHSIZE:
                fhp->fh_no_wcc = true;
                if (EX_WGATHER(exp))
                        fhp->fh_use_wgather = true;
                if (exp->ex_flags & NFSEXP_V4ROOT)
                        goto out;
        }

        return 0;
out:
        exp_put(exp);
        return error;
}

/**
 * __fh_verify - filehandle lookup and access checking
 * @rqstp: RPC transaction context, or NULL
 * @net: net namespace in which to perform the export lookup
 * @cred: RPC user credential
 * @client: RPC auth domain
 * @gssclient: RPC GSS auth domain, or NULL
 * @fhp: filehandle to be verified
 * @type: expected type of object pointed to by filehandle
 * @access: type of access needed to object
 *
 * See fh_verify() for further descriptions of @fhp, @type, and @access.
 */
static __be32
__fh_verify(struct svc_rqst *rqstp,
            struct net *net, struct svc_cred *cred,
            struct auth_domain *client,
            struct auth_domain *gssclient,
            struct svc_fh *fhp, umode_t type, int access)
{
        struct nfsd_net *nn = net_generic(net, nfsd_net_id);
        struct svc_export *exp = NULL;
        struct dentry   *dentry;
        __be32          error;

        if (!fhp->fh_dentry) {
                error = nfsd_set_fh_dentry(rqstp, net, cred, client,
                                           gssclient, fhp);
                if (error)
                        goto out;
        }
        dentry = fhp->fh_dentry;
        exp = fhp->fh_export;

        trace_nfsd_fh_verify(rqstp, fhp, type, access);

        /*
         * We still have to do all these permission checks, even when
         * fh_dentry is already set:
         *      - fh_verify may be called multiple times with different
         *        "access" arguments (e.g. nfsd_proc_create calls
         *        fh_verify(...,NFSD_MAY_EXEC) first, then later (in
         *        nfsd_create) calls fh_verify(...,NFSD_MAY_CREATE).
         *      - in the NFSv4 case, the filehandle may have been filled
         *        in by fh_compose, and given a dentry, but further
         *        compound operations performed with that filehandle
         *        still need permissions checks.  In the worst case, a
         *        mountpoint crossing may have changed the export
         *        options, and we may now need to use a different uid
         *        (for example, if different id-squashing options are in
         *        effect on the new filesystem).
         */
        error = check_pseudo_root(dentry, exp);
        if (error)
                goto out;

        error = nfsd_setuser_and_check_port(rqstp, cred, exp);
        if (error)
                goto out;

        error = nfsd_mode_check(dentry, type);
        if (error)
                goto out;

        /*
         * pseudoflavor restrictions are not enforced on NLM,
         * which clients virtually always use auth_sys for,
         * even while using RPCSEC_GSS for NFS.
         */
        if (access & NFSD_MAY_LOCK || access & NFSD_MAY_BYPASS_GSS)
                goto skip_pseudoflavor_check;
        /*
         * Clients may expect to be able to use auth_sys during mount,
         * even if they use gss for everything else; see section 2.3.2
         * of rfc 2623.
         */
        if (access & NFSD_MAY_BYPASS_GSS_ON_ROOT
                        && exp->ex_path.dentry == dentry)
                goto skip_pseudoflavor_check;

        error = check_nfsd_access(exp, rqstp);
        if (error)
                goto out;

skip_pseudoflavor_check:
        /* Finally, check access permissions. */
        error = nfsd_permission(cred, exp, dentry, access);
out:
        trace_nfsd_fh_verify_err(rqstp, fhp, type, access, error);
        if (error == nfserr_stale)
                nfsd_stats_fh_stale_inc(nn, exp);
        return error;
}

/**
 * fh_verify_local - filehandle lookup and access checking
 * @net: net namespace in which to perform the export lookup
 * @cred: RPC user credential
 * @client: RPC auth domain
 * @fhp: filehandle to be verified
 * @type: expected type of object pointed to by filehandle
 * @access: type of access needed to object
 *
 * This API can be used by callers who do not have an RPC
 * transaction context (ie are not running in an nfsd thread).
 *
 * See fh_verify() for further descriptions of @fhp, @type, and @access.
 */
__be32
fh_verify_local(struct net *net, struct svc_cred *cred,
                struct auth_domain *client, struct svc_fh *fhp,
                umode_t type, int access)
{
        return __fh_verify(NULL, net, cred, client, NULL,
                           fhp, type, access);
}

/**
 * fh_verify - filehandle lookup and access checking
 * @rqstp: pointer to current rpc request
 * @fhp: filehandle to be verified
 * @type: expected type of object pointed to by filehandle
 * @access: type of access needed to object
 *
 * Look up a dentry from the on-the-wire filehandle, check the client's
 * access to the export, and set the current task's credentials.
 *
 * Regardless of success or failure of fh_verify(), fh_put() should be
 * called on @fhp when the caller is finished with the filehandle.
 *
 * fh_verify() may be called multiple times on a given filehandle, for
 * example, when processing an NFSv4 compound.  The first call will look
 * up a dentry using the on-the-wire filehandle.  Subsequent calls will
 * skip the lookup and just perform the other checks and possibly change
 * the current task's credentials.
 *
 * @type specifies the type of object expected using one of the S_IF*
 * constants defined in include/linux/stat.h.  The caller may use zero
 * to indicate that it doesn't care, or a negative integer to indicate
 * that it expects something not of the given type.
 *
 * @access is formed from the NFSD_MAY_* constants defined in
 * fs/nfsd/vfs.h.
 */
__be32
fh_verify(struct svc_rqst *rqstp, struct svc_fh *fhp, umode_t type, int access)
{
        return __fh_verify(rqstp, SVC_NET(rqstp), &rqstp->rq_cred,
                           rqstp->rq_client, rqstp->rq_gssclient,
                           fhp, type, access);
}

/*
 * Compose a file handle for an NFS reply.
 *
 * Note that when first composed, the dentry may not yet have
 * an inode.  In this case a call to fh_update should be made
 * before the fh goes out on the wire ...
 */
static void _fh_update(struct svc_fh *fhp, struct svc_export *exp,
                struct dentry *dentry)
{
        if (dentry != exp->ex_path.dentry) {
                struct fid *fid = (struct fid *)
                        (fhp->fh_handle.fh_fsid + fhp->fh_handle.fh_size/4 - 1);
                int maxsize = (fhp->fh_maxsize - fhp->fh_handle.fh_size)/4;
                int fh_flags = (exp->ex_flags & NFSEXP_NOSUBTREECHECK) ? 0 :
                                EXPORT_FH_CONNECTABLE;
                int fileid_type =
                        exportfs_encode_fh(dentry, fid, &maxsize, fh_flags);

                fhp->fh_handle.fh_fileid_type =
                        fileid_type > 0 ? fileid_type : FILEID_INVALID;
                fhp->fh_handle.fh_size += maxsize * 4;
        } else {
                fhp->fh_handle.fh_fileid_type = FILEID_ROOT;
        }
}

static bool is_root_export(struct svc_export *exp)
{
        return exp->ex_path.dentry == exp->ex_path.dentry->d_sb->s_root;
}

static struct super_block *exp_sb(struct svc_export *exp)
{
        return exp->ex_path.dentry->d_sb;
}

static bool fsid_type_ok_for_exp(u8 fsid_type, struct svc_export *exp)
{
        switch (fsid_type) {
        case FSID_DEV:
                if (!old_valid_dev(exp_sb(exp)->s_dev))
                        return false;
                fallthrough;
        case FSID_MAJOR_MINOR:
        case FSID_ENCODE_DEV:
                return exp_sb(exp)->s_type->fs_flags & FS_REQUIRES_DEV;
        case FSID_NUM:
                return exp->ex_flags & NFSEXP_FSID;
        case FSID_UUID8:
        case FSID_UUID16:
                if (!is_root_export(exp))
                        return false;
                fallthrough;
        case FSID_UUID4_INUM:
        case FSID_UUID16_INUM:
                return exp->ex_uuid != NULL;
        }
        return true;
}


static void set_version_and_fsid_type(struct svc_fh *fhp, struct svc_export *exp, struct svc_fh *ref_fh)
{
        u8 version;
        u8 fsid_type;
retry:
        version = 1;
        if (ref_fh && ref_fh->fh_export == exp) {
                version = ref_fh->fh_handle.fh_version;
                fsid_type = ref_fh->fh_handle.fh_fsid_type;

                ref_fh = NULL;

                switch (version) {
                case 0xca:
                        fsid_type = FSID_DEV;
                        break;
                case 1:
                        break;
                default:
                        goto retry;
                }

                /*
                 * As the fsid -> filesystem mapping was guided by
                 * user-space, there is no guarantee that the filesystem
                 * actually supports that fsid type. If it doesn't we
                 * loop around again without ref_fh set.
                 */
                if (!fsid_type_ok_for_exp(fsid_type, exp))
                        goto retry;
        } else if (exp->ex_flags & NFSEXP_FSID) {
                fsid_type = FSID_NUM;
        } else if (exp->ex_uuid) {
                if (fhp->fh_maxsize >= 64) {
                        if (is_root_export(exp))
                                fsid_type = FSID_UUID16;
                        else
                                fsid_type = FSID_UUID16_INUM;
                } else {
                        if (is_root_export(exp))
                                fsid_type = FSID_UUID8;
                        else
                                fsid_type = FSID_UUID4_INUM;
                }
        } else if (!old_valid_dev(exp_sb(exp)->s_dev))
                /* for newer device numbers, we must use a newer fsid format */
                fsid_type = FSID_ENCODE_DEV;
        else
                fsid_type = FSID_DEV;
        fhp->fh_handle.fh_version = version;
        if (version)
                fhp->fh_handle.fh_fsid_type = fsid_type;
}

__be32
fh_compose(struct svc_fh *fhp, struct svc_export *exp, struct dentry *dentry,
           struct svc_fh *ref_fh)
{
        /* ref_fh is a reference file handle.
         * if it is non-null and for the same filesystem, then we should compose
         * a filehandle which is of the same version, where possible.
         */

        struct inode * inode = d_inode(dentry);
        dev_t ex_dev = exp_sb(exp)->s_dev;

        dprintk("nfsd: fh_compose(exp %02x:%02x/%ld %pd2, ino=%ld)\n",
                MAJOR(ex_dev), MINOR(ex_dev),
                (long) d_inode(exp->ex_path.dentry)->i_ino,
                dentry,
                (inode ? inode->i_ino : 0));

        /* Choose filehandle version and fsid type based on
         * the reference filehandle (if it is in the same export)
         * or the export options.
         */
        set_version_and_fsid_type(fhp, exp, ref_fh);

        /* If we have a ref_fh, then copy the fh_no_wcc setting from it. */
        fhp->fh_no_wcc = ref_fh ? ref_fh->fh_no_wcc : false;

        if (ref_fh == fhp)
                fh_put(ref_fh);

        if (fhp->fh_dentry) {
                printk(KERN_ERR "fh_compose: fh %pd2 not initialized!\n",
                       dentry);
        }
        if (fhp->fh_maxsize < NFS_FHSIZE)
                printk(KERN_ERR "fh_compose: called with maxsize %d! %pd2\n",
                       fhp->fh_maxsize,
                       dentry);

        fhp->fh_dentry = dget(dentry); /* our internal copy */
        fhp->fh_export = exp_get(exp);

        fhp->fh_handle.fh_size =
                key_len(fhp->fh_handle.fh_fsid_type) + 4;
        fhp->fh_handle.fh_auth_type = 0;

        mk_fsid(fhp->fh_handle.fh_fsid_type,
                fhp->fh_handle.fh_fsid,
                ex_dev,
                d_inode(exp->ex_path.dentry)->i_ino,
                exp->ex_fsid, exp->ex_uuid);

        if (inode)
                _fh_update(fhp, exp, dentry);
        if (fhp->fh_handle.fh_fileid_type == FILEID_INVALID) {
                fh_put(fhp);
                return nfserr_stale;
        }

        return 0;
}

/*
 * Update file handle information after changing a dentry.
 * This is only called by nfsd_create, nfsd_create_v3 and nfsd_proc_create
 */
__be32
fh_update(struct svc_fh *fhp)
{
        struct dentry *dentry;

        if (!fhp->fh_dentry)
                goto out_bad;

        dentry = fhp->fh_dentry;
        if (d_really_is_negative(dentry))
                goto out_negative;
        if (fhp->fh_handle.fh_fileid_type != FILEID_ROOT)
                return 0;

        _fh_update(fhp, fhp->fh_export, dentry);
        if (fhp->fh_handle.fh_fileid_type == FILEID_INVALID)
                return nfserr_stale;
        return 0;
out_bad:
        printk(KERN_ERR "fh_update: fh not verified!\n");
        return nfserr_serverfault;
out_negative:
        printk(KERN_ERR "fh_update: %pd2 still negative!\n",
                dentry);
        return nfserr_serverfault;
}

/**
 * fh_fill_pre_attrs - Fill in pre-op attributes
 * @fhp: file handle to be updated
 *
 */
__be32 __must_check fh_fill_pre_attrs(struct svc_fh *fhp)
{
        bool v4 = (fhp->fh_maxsize == NFS4_FHSIZE);
        struct inode *inode;
        struct kstat stat;
        __be32 err;

        if (fhp->fh_no_wcc || fhp->fh_pre_saved)
                return nfs_ok;

        inode = d_inode(fhp->fh_dentry);
        err = fh_getattr(fhp, &stat);
        if (err)
                return err;

        if (v4)
                fhp->fh_pre_change = nfsd4_change_attribute(&stat, inode);

        fhp->fh_pre_mtime = stat.mtime;
        fhp->fh_pre_ctime = stat.ctime;
        fhp->fh_pre_size  = stat.size;
        fhp->fh_pre_saved = true;
        return nfs_ok;
}

/**
 * fh_fill_post_attrs - Fill in post-op attributes
 * @fhp: file handle to be updated
 *
 */
__be32 fh_fill_post_attrs(struct svc_fh *fhp)
{
        bool v4 = (fhp->fh_maxsize == NFS4_FHSIZE);
        struct inode *inode = d_inode(fhp->fh_dentry);
        __be32 err;

        if (fhp->fh_no_wcc)
                return nfs_ok;

        if (fhp->fh_post_saved)
                printk("nfsd: inode locked twice during operation.\n");

        err = fh_getattr(fhp, &fhp->fh_post_attr);
        if (err)
                return err;

        fhp->fh_post_saved = true;
        if (v4)
                fhp->fh_post_change =
                        nfsd4_change_attribute(&fhp->fh_post_attr, inode);
        return nfs_ok;
}

/**
 * fh_fill_both_attrs - Fill pre-op and post-op attributes
 * @fhp: file handle to be updated
 *
 * This is used when the directory wasn't changed, but wcc attributes
 * are needed anyway.
 */
__be32 __must_check fh_fill_both_attrs(struct svc_fh *fhp)
{
        __be32 err;

        err = fh_fill_post_attrs(fhp);
        if (err)
                return err;

        fhp->fh_pre_change = fhp->fh_post_change;
        fhp->fh_pre_mtime = fhp->fh_post_attr.mtime;
        fhp->fh_pre_ctime = fhp->fh_post_attr.ctime;
        fhp->fh_pre_size = fhp->fh_post_attr.size;
        fhp->fh_pre_saved = true;
        return nfs_ok;
}

/*
 * Release a file handle.
 */
void
fh_put(struct svc_fh *fhp)
{
        struct dentry * dentry = fhp->fh_dentry;
        struct svc_export * exp = fhp->fh_export;
        if (dentry) {
                fhp->fh_dentry = NULL;
                dput(dentry);
                fh_clear_pre_post_attrs(fhp);
        }
        fh_drop_write(fhp);
        if (exp) {
                exp_put(exp);
                fhp->fh_export = NULL;
        }
        fhp->fh_no_wcc = false;
        return;
}

/*
 * Shorthand for dprintk()'s
 */
char * SVCFH_fmt(struct svc_fh *fhp)
{
        struct knfsd_fh *fh = &fhp->fh_handle;
        static char buf[2+1+1+64*3+1];

        if (fh->fh_size < 0 || fh->fh_size> 64)
                return "bad-fh";
        sprintf(buf, "%d: %*ph", fh->fh_size, fh->fh_size, fh->fh_raw);
        return buf;
}

enum fsid_source fsid_source(const struct svc_fh *fhp)
{
        if (fhp->fh_handle.fh_version != 1)
                return FSIDSOURCE_DEV;
        switch(fhp->fh_handle.fh_fsid_type) {
        case FSID_DEV:
        case FSID_ENCODE_DEV:
        case FSID_MAJOR_MINOR:
                if (exp_sb(fhp->fh_export)->s_type->fs_flags & FS_REQUIRES_DEV)
                        return FSIDSOURCE_DEV;
                break;
        case FSID_NUM:
                if (fhp->fh_export->ex_flags & NFSEXP_FSID)
                        return FSIDSOURCE_FSID;
                break;
        default:
                break;
        }
        /* either a UUID type filehandle, or the filehandle doesn't
         * match the export.
         */
        if (fhp->fh_export->ex_flags & NFSEXP_FSID)
                return FSIDSOURCE_FSID;
        if (fhp->fh_export->ex_uuid)
                return FSIDSOURCE_UUID;
        return FSIDSOURCE_DEV;
}

/*
 * We could use i_version alone as the change attribute.  However, i_version
 * can go backwards on a regular file after an unclean shutdown.  On its own
 * that doesn't necessarily cause a problem, but if i_version goes backwards
 * and then is incremented again it could reuse a value that was previously
 * used before boot, and a client who queried the two values might incorrectly
 * assume nothing changed.
 *
 * By using both ctime and the i_version counter we guarantee that as long as
 * time doesn't go backwards we never reuse an old value. If the filesystem
 * advertises STATX_ATTR_CHANGE_MONOTONIC, then this mitigation is not
 * needed.
 *
 * We only need to do this for regular files as well. For directories, we
 * assume that the new change attr is always logged to stable storage in some
 * fashion before the results can be seen.
 */
u64 nfsd4_change_attribute(const struct kstat *stat, const struct inode *inode)
{
        u64 chattr;

        if (stat->result_mask & STATX_CHANGE_COOKIE) {
                chattr = stat->change_cookie;
                if (S_ISREG(inode->i_mode) &&
                    !(stat->attributes & STATX_ATTR_CHANGE_MONOTONIC)) {
                        chattr += (u64)stat->ctime.tv_sec << 30;
                        chattr += stat->ctime.tv_nsec;
                }
        } else {
                chattr = time_to_chattr(&stat->ctime);
        }
        return chattr;
}