nfsd4: use xdr_reserve_space in attribute encoding

This is a cosmetic change for now; no change in behavior.

Note we're just depending on xdr_reserve_space to do the bounds checking
for us, we're not really depending on its adjustment of iovec or xdr_buf
lengths yet, as those are fixed up by as necessary after the fact by
read-link operations and by nfs4svc_encode_compoundres.  However we do
have to update xdr->iov on read-like operations to prevent
xdr_reserve_space from messing with the already-fixed-up length of the
the head.

When the attribute encoding fails partway through we have to undo the
length adjustments made so far.  We do it manually for now, but later
patches will add an xdr_truncate_encode() helper to handle cases like
this.

Signed-off-by: J. Bruce Fields <bfields@redhat.com>

6 files changed, 203 insertions, 145 deletions

diff --git a/fs/nfsd/acl.h b/fs/nfsd/acl.h
index b481e1f..a986ceb 100644
--- a/fs/nfsd/acl.h
+++ b/fs/nfsd/acl.h
@@ -49,7 +49,7 @@ struct svc_rqst;
 
 struct nfs4_acl *nfs4_acl_new(int);
 int nfs4_acl_get_whotype(char *, u32);
-__be32 nfs4_acl_write_who(int who, __be32 **p, int *len);
+__be32 nfs4_acl_write_who(struct xdr_stream *xdr, int who);
 
 int nfsd4_get_nfs4_acl(struct svc_rqst *rqstp, struct dentry *dentry,
 		struct nfs4_acl **acl);
diff --git a/fs/nfsd/idmap.h b/fs/nfsd/idmap.h
index 66e58db..a3f3490 100644
--- a/fs/nfsd/idmap.h
+++ b/fs/nfsd/idmap.h
@@ -56,7 +56,7 @@ static inline void nfsd_idmap_shutdown(struct net *net)
 
 __be32 nfsd_map_name_to_uid(struct svc_rqst *, const char *, size_t, kuid_t *);
 __be32 nfsd_map_name_to_gid(struct svc_rqst *, const char *, size_t, kgid_t *);
-__be32 nfsd4_encode_user(struct svc_rqst *, kuid_t, __be32 **, int *);
-__be32 nfsd4_encode_group(struct svc_rqst *, kgid_t, __be32 **, int *);
+__be32 nfsd4_encode_user(struct xdr_stream *, struct svc_rqst *, kuid_t);
+__be32 nfsd4_encode_group(struct xdr_stream *, struct svc_rqst *, kgid_t);
 
 #endif /* LINUX_NFSD_IDMAP_H */
diff --git a/fs/nfsd/nfs4acl.c b/fs/nfsd/nfs4acl.c
index 7c7c025..d714156 100644
--- a/fs/nfsd/nfs4acl.c
+++ b/fs/nfsd/nfs4acl.c
@@ -919,20 +919,19 @@ nfs4_acl_get_whotype(char *p, u32 len)
 	return NFS4_ACL_WHO_NAMED;
 }
 
-__be32 nfs4_acl_write_who(int who, __be32 **p, int *len)
+__be32 nfs4_acl_write_who(struct xdr_stream *xdr, int who)
 {
+	__be32 *p;
 	int i;
-	int bytes;
 
 	for (i = 0; i < ARRAY_SIZE(s2t_map); i++) {
 		if (s2t_map[i].type != who)
 			continue;
-		bytes = 4 + (XDR_QUADLEN(s2t_map[i].stringlen) << 2);
-		if (bytes > *len)
+		p = xdr_reserve_space(xdr, s2t_map[i].stringlen + 4);
+		if (!p)
 			return nfserr_resource;
-		*p = xdr_encode_opaque(*p, s2t_map[i].string,
+		p = xdr_encode_opaque(p, s2t_map[i].string,
 					s2t_map[i].stringlen);
-		*len -= bytes;
 		return 0;
 	}
 	WARN_ON_ONCE(1);
diff --git a/fs/nfsd/nfs4idmap.c b/fs/nfsd/nfs4idmap.c
index c0dfde6..a0ab0a8 100644
--- a/fs/nfsd/nfs4idmap.c
+++ b/fs/nfsd/nfs4idmap.c
@@ -551,44 +551,43 @@ idmap_name_to_id(struct svc_rqst *rqstp, int type, const char *name, u32 namelen
 	return 0;
 }
 
-static __be32 encode_ascii_id(u32 id, __be32 **p, int *buflen)
+static __be32 encode_ascii_id(struct xdr_stream *xdr, u32 id)
 {
 	char buf[11];
 	int len;
-	int bytes;
+	__be32 *p;
 
 	len = sprintf(buf, "%u", id);
-	bytes = 4 + (XDR_QUADLEN(len) << 2);
-	if (bytes > *buflen)
+	p = xdr_reserve_space(xdr, len + 4);
+	if (!p)
 		return nfserr_resource;
-	*p = xdr_encode_opaque(*p, buf, len);
-	*buflen -= bytes;
+	p = xdr_encode_opaque(p, buf, len);
 	return 0;
 }
 
-static __be32 idmap_id_to_name(struct svc_rqst *rqstp, int type, u32 id, __be32 **p, int *buflen)
+static __be32 idmap_id_to_name(struct xdr_stream *xdr,
+			       struct svc_rqst *rqstp, int type, u32 id)
 {
 	struct ent *item, key = {
 		.id = id,
 		.type = type,
 	};
+	__be32 *p;
 	int ret;
-	int bytes;
 	struct nfsd_net *nn = net_generic(SVC_NET(rqstp), nfsd_net_id);
 
 	strlcpy(key.authname, rqst_authname(rqstp), sizeof(key.authname));
 	ret = idmap_lookup(rqstp, idtoname_lookup, &key, nn->idtoname_cache, &item);
 	if (ret == -ENOENT)
-		return encode_ascii_id(id, p, buflen);
+		return encode_ascii_id(xdr, id);
 	if (ret)
 		return nfserrno(ret);
 	ret = strlen(item->name);
 	WARN_ON_ONCE(ret > IDMAP_NAMESZ);
-	bytes = 4 + (XDR_QUADLEN(ret) << 2);
-	if (bytes > *buflen)
+	p = xdr_reserve_space(xdr, ret + 4);
+	if (!p)
 		return nfserr_resource;
-	*p = xdr_encode_opaque(*p, item->name, ret);
-	*buflen -= bytes;
+	p = xdr_encode_opaque(p, item->name, ret);
 	cache_put(&item->h, nn->idtoname_cache);
 	return 0;
 }
@@ -622,11 +621,12 @@ do_name_to_id(struct svc_rqst *rqstp, int type, const char *name, u32 namelen, u
 	return idmap_name_to_id(rqstp, type, name, namelen, id);
 }
 
-static __be32 encode_name_from_id(struct svc_rqst *rqstp, int type, u32 id, __be32 **p, int *buflen)
+static __be32 encode_name_from_id(struct xdr_stream *xdr,
+				  struct svc_rqst *rqstp, int type, u32 id)
 {
 	if (nfs4_disable_idmapping && rqstp->rq_cred.cr_flavor < RPC_AUTH_GSS)
-		return encode_ascii_id(id, p, buflen);
-	return idmap_id_to_name(rqstp, type, id, p, buflen);
+		return encode_ascii_id(xdr, id);
+	return idmap_id_to_name(xdr, rqstp, type, id);
 }
 
 __be32
@@ -655,14 +655,16 @@ nfsd_map_name_to_gid(struct svc_rqst *rqstp, const char *name, size_t namelen,
 	return status;
 }
 
-__be32 nfsd4_encode_user(struct svc_rqst *rqstp, kuid_t uid,  __be32 **p, int *buflen)
+__be32 nfsd4_encode_user(struct xdr_stream *xdr, struct svc_rqst *rqstp,
+			 kuid_t uid)
 {
 	u32 id = from_kuid(&init_user_ns, uid);
-	return encode_name_from_id(rqstp, IDMAP_TYPE_USER, id, p, buflen);
+	return encode_name_from_id(xdr, rqstp, IDMAP_TYPE_USER, id);
 }
 
-__be32 nfsd4_encode_group(struct svc_rqst *rqstp, kgid_t gid, __be32 **p, int *buflen)
+__be32 nfsd4_encode_group(struct xdr_stream *xdr, struct svc_rqst *rqstp,
+			  kgid_t gid)
 {
 	u32 id = from_kgid(&init_user_ns, gid);
-	return encode_name_from_id(rqstp, IDMAP_TYPE_GROUP, id, p, buflen);
+	return encode_name_from_id(xdr, rqstp, IDMAP_TYPE_GROUP, id);
 }
diff --git a/fs/nfsd/nfs4proc.c b/fs/nfsd/nfs4proc.c
index bf8cddf..41c7c0a 100644
--- a/fs/nfsd/nfs4proc.c
+++ b/fs/nfsd/nfs4proc.c
@@ -1259,6 +1259,7 @@ static void svcxdr_init_encode(struct svc_rqst *rqstp,
 	struct kvec *head = buf->head;
 
 	xdr->buf = buf;
+	xdr->iov = head;
 	xdr->p   = head->iov_base + head->iov_len;
 	xdr->end = head->iov_base + PAGE_SIZE - 2 * RPC_MAX_AUTH_SIZE;
 }
diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c
index 2ed8036..27d1e94 100644
--- a/fs/nfsd/nfs4xdr.c
+++ b/fs/nfsd/nfs4xdr.c
@@ -1755,18 +1755,20 @@ static void write_cinfo(__be32 **p, struct nfsd4_change_info *c)
 /* Encode as an array of strings the string given with components
  * separated @sep, escaped with esc_enter and esc_exit.
  */
-static __be32 nfsd4_encode_components_esc(char sep, char *components,
-				   __be32 **pp, int *buflen,
-				   char esc_enter, char esc_exit)
+static __be32 nfsd4_encode_components_esc(struct xdr_stream *xdr, char sep,
+					  char *components, char esc_enter,
+					  char esc_exit)
 {
-	__be32 *p = *pp;
-	__be32 *countp = p;
+	__be32 *p;
+	__be32 *countp;
 	int strlen, count=0;
 	char *str, *end, *next;
 
 	dprintk("nfsd4_encode_components(%s)\n", components);
-	if ((*buflen -= 4) < 0)
+	p = xdr_reserve_space(xdr, 4);
+	if (!p)
 		return nfserr_resource;
+	countp = p;
 	WRITE32(0); /* We will fill this in with @count later */
 	end = str = components;
 	while (*end) {
@@ -1789,7 +1791,8 @@ static __be32 nfsd4_encode_components_esc(char sep, char *components,
 
 		strlen = end - str;
 		if (strlen) {
-			if ((*buflen -= ((XDR_QUADLEN(strlen) << 2) + 4)) < 0)
+			p = xdr_reserve_space(xdr, strlen + 4);
+			if (!p)
 				return nfserr_resource;
 			WRITE32(strlen);
 			WRITEMEM(str, strlen);
@@ -1799,7 +1802,6 @@ static __be32 nfsd4_encode_components_esc(char sep, char *components,
 			end++;
 		str = end;
 	}
-	*pp = p;
 	p = countp;
 	WRITE32(count);
 	return 0;
@@ -1808,40 +1810,39 @@ static __be32 nfsd4_encode_components_esc(char sep, char *components,
 /* Encode as an array of strings the string given with components
  * separated @sep.
  */
-static __be32 nfsd4_encode_components(char sep, char *components,
-				   __be32 **pp, int *buflen)
+static __be32 nfsd4_encode_components(struct xdr_stream *xdr, char sep,
+				      char *components)
 {
-	return nfsd4_encode_components_esc(sep, components, pp, buflen, 0, 0);
+	return nfsd4_encode_components_esc(xdr, sep, components, 0, 0);
 }
 
 /*
  * encode a location element of a fs_locations structure
  */
-static __be32 nfsd4_encode_fs_location4(struct nfsd4_fs_location *location,
-				    __be32 **pp, int *buflen)
+static __be32 nfsd4_encode_fs_location4(struct xdr_stream *xdr,
+					struct nfsd4_fs_location *location)
 {
 	__be32 status;
-	__be32 *p = *pp;
 
-	status = nfsd4_encode_components_esc(':', location->hosts, &p, buflen,
+	status = nfsd4_encode_components_esc(xdr, ':', location->hosts,
 						'[', ']');
 	if (status)
 		return status;
-	status = nfsd4_encode_components('/', location->path, &p, buflen);
+	status = nfsd4_encode_components(xdr, '/', location->path);
 	if (status)
 		return status;
-	*pp = p;
 	return 0;
 }
 
 /*
  * Encode a path in RFC3530 'pathname4' format
  */
-static __be32 nfsd4_encode_path(const struct path *root,
-		const struct path *path, __be32 **pp, int *buflen)
+static __be32 nfsd4_encode_path(struct xdr_stream *xdr,
+				const struct path *root,
+				const struct path *path)
 {
 	struct path cur = *path;
-	__be32 *p = *pp;
+	__be32 *p;
 	struct dentry **components = NULL;
 	unsigned int ncomponents = 0;
 	__be32 err = nfserr_jukebox;
@@ -1872,9 +1873,9 @@ static __be32 nfsd4_encode_path(const struct path *root,
 		components[ncomponents++] = cur.dentry;
 		cur.dentry = dget_parent(cur.dentry);
 	}
-
-	*buflen -= 4;
-	if (*buflen < 0)
+	err = nfserr_resource;
+	p = xdr_reserve_space(xdr, 4);
+	if (!p)
 		goto out_free;
 	WRITE32(ncomponents);
 
@@ -1884,8 +1885,8 @@ static __be32 nfsd4_encode_path(const struct path *root,
 
 		spin_lock(&dentry->d_lock);
 		len = dentry->d_name.len;
-		*buflen -= 4 + (XDR_QUADLEN(len) << 2);
-		if (*buflen < 0) {
+		p = xdr_reserve_space(xdr, len + 4);
+		if (!p) {
 			spin_unlock(&dentry->d_lock);
 			goto out_free;
 		}
@@ -1897,7 +1898,6 @@ static __be32 nfsd4_encode_path(const struct path *root,
 		ncomponents--;
 	}
 
-	*pp = p;
 	err = 0;
 out_free:
 	dprintk(")\n");
@@ -1908,8 +1908,8 @@ out_free:
 	return err;
 }
 
-static __be32 nfsd4_encode_fsloc_fsroot(struct svc_rqst *rqstp,
-		const struct path *path, __be32 **pp, int *buflen)
+static __be32 nfsd4_encode_fsloc_fsroot(struct xdr_stream *xdr,
+			struct svc_rqst *rqstp, const struct path *path)
 {
 	struct svc_export *exp_ps;
 	__be32 res;
@@ -1917,7 +1917,7 @@ static __be32 nfsd4_encode_fsloc_fsroot(struct svc_rqst *rqstp,
 	exp_ps = rqst_find_fsidzero_export(rqstp);
 	if (IS_ERR(exp_ps))
 		return nfserrno(PTR_ERR(exp_ps));
-	res = nfsd4_encode_path(&exp_ps->ex_path, path, pp, buflen);
+	res = nfsd4_encode_path(xdr, &exp_ps->ex_path, path);
 	exp_put(exp_ps);
 	return res;
 }
@@ -1925,28 +1925,26 @@ static __be32 nfsd4_encode_fsloc_fsroot(struct svc_rqst *rqstp,
 /*
  *  encode a fs_locations structure
  */
-static __be32 nfsd4_encode_fs_locations(struct svc_rqst *rqstp,
-				     struct svc_export *exp,
-				     __be32 **pp, int *buflen)
+static __be32 nfsd4_encode_fs_locations(struct xdr_stream *xdr,
+			struct svc_rqst *rqstp, struct svc_export *exp)
 {
 	__be32 status;
 	int i;
-	__be32 *p = *pp;
+	__be32 *p;
 	struct nfsd4_fs_locations *fslocs = &exp->ex_fslocs;
 
-	status = nfsd4_encode_fsloc_fsroot(rqstp, &exp->ex_path, &p, buflen);
+	status = nfsd4_encode_fsloc_fsroot(xdr, rqstp, &exp->ex_path);
 	if (status)
 		return status;
-	if ((*buflen -= 4) < 0)
+	p = xdr_reserve_space(xdr, 4);
+	if (!p)
 		return nfserr_resource;
 	WRITE32(fslocs->locations_count);
 	for (i=0; i<fslocs->locations_count; i++) {
-		status = nfsd4_encode_fs_location4(&fslocs->locations[i],
-						   &p, buflen);
+		status = nfsd4_encode_fs_location4(xdr, &fslocs->locations[i]);
 		if (status)
 			return status;
 	}
-	*pp = p;
 	return 0;
 }
 
@@ -1965,15 +1963,15 @@ static u32 nfs4_file_type(umode_t mode)
 }
 
 static inline __be32
-nfsd4_encode_aclname(struct svc_rqst *rqstp, struct nfs4_ace *ace,
-		__be32 **p, int *buflen)
+nfsd4_encode_aclname(struct xdr_stream *xdr, struct svc_rqst *rqstp,
+		     struct nfs4_ace *ace)
 {
 	if (ace->whotype != NFS4_ACL_WHO_NAMED)
-		return nfs4_acl_write_who(ace->whotype, p, buflen);
+		return nfs4_acl_write_who(xdr, ace->whotype);
 	else if (ace->flag & NFS4_ACE_IDENTIFIER_GROUP)
-		return nfsd4_encode_group(rqstp, ace->who_gid, p, buflen);
+		return nfsd4_encode_group(xdr, rqstp, ace->who_gid);
 	else
-		return nfsd4_encode_user(rqstp, ace->who_uid, p, buflen);
+		return nfsd4_encode_user(xdr, rqstp, ace->who_uid);
 }
 
 #define WORD0_ABSENT_FS_ATTRS (FATTR4_WORD0_FS_LOCATIONS | FATTR4_WORD0_FSID | \
@@ -1982,31 +1980,28 @@ nfsd4_encode_aclname(struct svc_rqst *rqstp, struct nfs4_ace *ace,
 
 #ifdef CONFIG_NFSD_V4_SECURITY_LABEL
 static inline __be32
-nfsd4_encode_security_label(struct svc_rqst *rqstp, void *context, int len, __be32 **pp, int *buflen)
+nfsd4_encode_security_label(struct xdr_stream *xdr, struct svc_rqst *rqstp,
+			    void *context, int len)
 {
-	__be32 *p = *pp;
+	__be32 *p;
 
-	if (*buflen < ((XDR_QUADLEN(len) << 2) + 4 + 4 + 4))
+	p = xdr_reserve_space(xdr, len + 4 + 4 + 4);
+	if (!p)
 		return nfserr_resource;
 
 	/*
 	 * For now we use a 0 here to indicate the null translation; in
 	 * the future we may place a call to translation code here.
 	 */
-	if ((*buflen -= 8) < 0)
-		return nfserr_resource;
-
 	WRITE32(0); /* lfs */
 	WRITE32(0); /* pi */
 	p = xdr_encode_opaque(p, context, len);
-	*buflen -= (XDR_QUADLEN(len) << 2) + 4;
-
-	*pp = p;
 	return 0;
 }
 #else
 static inline __be32
-nfsd4_encode_security_label(struct svc_rqst *rqstp, void *context, int len, __be32 **pp, int *buflen)
+nfsd4_encode_security_label(struct xdr_stream *xdr, struct svc_rqst *rqstp,
+			    void *context, int len)
 { return 0; }
 #endif
 
@@ -2058,8 +2053,8 @@ nfsd4_encode_fattr(struct xdr_stream *xdr, struct svc_fh *fhp,
 	struct kstat stat;
 	struct svc_fh *tempfh = NULL;
 	struct kstatfs statfs;
-	__be32 *p = xdr->p;
-	int buflen = xdr->buf->buflen;
+	__be32 *p;
+	__be32 *start = xdr->p;
 	__be32 *attrlenp;
 	u32 dummy;
 	u64 dummy64;
@@ -2144,24 +2139,30 @@ nfsd4_encode_fattr(struct xdr_stream *xdr, struct svc_fh *fhp,
 #endif /* CONFIG_NFSD_V4_SECURITY_LABEL */
 
 	if (bmval2) {
-		if ((buflen -= 16) < 0)
+		p = xdr_reserve_space(xdr, 16);
+		if (!p)
 			goto out_resource;
 		WRITE32(3);
 		WRITE32(bmval0);
 		WRITE32(bmval1);
 		WRITE32(bmval2);
 	} else if (bmval1) {
-		if ((buflen -= 12) < 0)
+		p = xdr_reserve_space(xdr, 12);
+		if (!p)
 			goto out_resource;
 		WRITE32(2);
 		WRITE32(bmval0);
 		WRITE32(bmval1);
 	} else {
-		if ((buflen -= 8) < 0)
+		p = xdr_reserve_space(xdr, 8);
+		if (!p)
 			goto out_resource;
 		WRITE32(1);
 		WRITE32(bmval0);
 	}
+	p = xdr_reserve_space(xdr, 4);
+	if (!p)
+		goto out_resource;
 	attrlenp = p++;                /* to be backfilled later */
 
 	if (bmval0 & FATTR4_WORD0_SUPPORTED_ATTRS) {
@@ -2174,13 +2175,15 @@ nfsd4_encode_fattr(struct xdr_stream *xdr, struct svc_fh *fhp,
 		if (!contextsupport)
 			word2 &= ~FATTR4_WORD2_SECURITY_LABEL;
 		if (!word2) {
-			if ((buflen -= 12) < 0)
+			p = xdr_reserve_space(xdr, 12);
+			if (!p)
 				goto out_resource;
 			WRITE32(2);
 			WRITE32(word0);
 			WRITE32(word1);
 		} else {
-			if ((buflen -= 16) < 0)
+			p = xdr_reserve_space(xdr, 16);
+			if (!p)
 				goto out_resource;
 			WRITE32(3);
 			WRITE32(word0);
@@ -2189,7 +2192,8 @@ nfsd4_encode_fattr(struct xdr_stream *xdr, struct svc_fh *fhp,
 		}
 	}
 	if (bmval0 & FATTR4_WORD0_TYPE) {
-		if ((buflen -= 4) < 0)
+		p = xdr_reserve_space(xdr, 4);
+		if (!p)
 			goto out_resource;
 		dummy = nfs4_file_type(stat.mode);
 		if (dummy == NF4BAD) {
@@ -2199,7 +2203,8 @@ nfsd4_encode_fattr(struct xdr_stream *xdr, struct svc_fh *fhp,
 		WRITE32(dummy);
 	}
 	if (bmval0 & FATTR4_WORD0_FH_EXPIRE_TYPE) {
-		if ((buflen -= 4) < 0)
+		p = xdr_reserve_space(xdr, 4);
+		if (!p)
 			goto out_resource;
 		if (exp->ex_flags & NFSEXP_NOSUBTREECHECK)
 			WRITE32(NFS4_FH_PERSISTENT);
@@ -2207,32 +2212,38 @@ nfsd4_encode_fattr(struct xdr_stream *xdr, struct svc_fh *fhp,
 			WRITE32(NFS4_FH_PERSISTENT|NFS4_FH_VOL_RENAME);
 	}
 	if (bmval0 & FATTR4_WORD0_CHANGE) {
-		if ((buflen -= 8) < 0)
+		p = xdr_reserve_space(xdr, 8);
+		if (!p)
 			goto out_resource;
 		write_change(&p, &stat, dentry->d_inode);
 	}
 	if (bmval0 & FATTR4_WORD0_SIZE) {
-		if ((buflen -= 8) < 0)
+		p = xdr_reserve_space(xdr, 8);
+		if (!p)
 			goto out_resource;
 		WRITE64(stat.size);
 	}
 	if (bmval0 & FATTR4_WORD0_LINK_SUPPORT) {
-		if ((buflen -= 4) < 0)
+		p = xdr_reserve_space(xdr, 4);
+		if (!p)
 			goto out_resource;
 		WRITE32(1);
 	}
 	if (bmval0 & FATTR4_WORD0_SYMLINK_SUPPORT) {
-		if ((buflen -= 4) < 0)
+		p = xdr_reserve_space(xdr, 4);
+		if (!p)
 			goto out_resource;
 		WRITE32(1);
 	}
 	if (bmval0 & FATTR4_WORD0_NAMED_ATTR) {
-		if ((buflen -= 4) < 0)
+		p = xdr_reserve_space(xdr, 4);
+		if (!p)
 			goto out_resource;
 		WRITE32(0);
 	}
 	if (bmval0 & FATTR4_WORD0_FSID) {
-		if ((buflen -= 16) < 0)
+		p = xdr_reserve_space(xdr, 16);
+		if (!p)
 			goto out_resource;
 		if (exp->ex_fslocs.migrated) {
 			WRITE64(NFS4_REFERRAL_FSID_MAJOR);
@@ -2254,17 +2265,20 @@ nfsd4_encode_fattr(struct xdr_stream *xdr, struct svc_fh *fhp,
 		}
 	}
 	if (bmval0 & FATTR4_WORD0_UNIQUE_HANDLES) {
-		if ((buflen -= 4) < 0)
+		p = xdr_reserve_space(xdr, 4);
+		if (!p)
 			goto out_resource;
 		WRITE32(0);
 	}
 	if (bmval0 & FATTR4_WORD0_LEASE_TIME) {
-		if ((buflen -= 4) < 0)
+		p = xdr_reserve_space(xdr, 4);
+		if (!p)
 			goto out_resource;
 		WRITE32(nn->nfsd4_lease);
 	}
 	if (bmval0 & FATTR4_WORD0_RDATTR_ERROR) {
-		if ((buflen -= 4) < 0)
+		p = xdr_reserve_space(xdr, 4);
+		if (!p)
 			goto out_resource;
 		WRITE32(rdattr_err);
 	}
@@ -2272,198 +2286,229 @@ nfsd4_encode_fattr(struct xdr_stream *xdr, struct svc_fh *fhp,
 		struct nfs4_ace *ace;
 
 		if (acl == NULL) {
-			if ((buflen -= 4) < 0)
+			p = xdr_reserve_space(xdr, 4);
+			if (!p)
 				goto out_resource;
 
 			WRITE32(0);
 			goto out_acl;
 		}
-		if ((buflen -= 4) < 0)
+		p = xdr_reserve_space(xdr, 4);
+		if (!p)
 			goto out_resource;
 		WRITE32(acl->naces);
 
 		for (ace = acl->aces; ace < acl->aces + acl->naces; ace++) {
-			if ((buflen -= 4*3) < 0)
+			p = xdr_reserve_space(xdr, 4*3);
+			if (!p)
 				goto out_resource;
 			WRITE32(ace->type);
 			WRITE32(ace->flag);
 			WRITE32(ace->access_mask & NFS4_ACE_MASK_ALL);
-			status = nfsd4_encode_aclname(rqstp, ace, &p, &buflen);
+			status = nfsd4_encode_aclname(xdr, rqstp, ace);
 			if (status)
 				goto out;
 		}
 	}
 out_acl:
 	if (bmval0 & FATTR4_WORD0_ACLSUPPORT) {
-		if ((buflen -= 4) < 0)
+		p = xdr_reserve_space(xdr, 4);
+		if (!p)
 			goto out_resource;
 		WRITE32(aclsupport ?
 			ACL4_SUPPORT_ALLOW_ACL|ACL4_SUPPORT_DENY_ACL : 0);
 	}
 	if (bmval0 & FATTR4_WORD0_CANSETTIME) {
-		if ((buflen -= 4) < 0)
+		p = xdr_reserve_space(xdr, 4);
+		if (!p)
 			goto out_resource;
 		WRITE32(1);
 	}
 	if (bmval0 & FATTR4_WORD0_CASE_INSENSITIVE) {
-		if ((buflen -= 4) < 0)
+		p = xdr_reserve_space(xdr, 4);
+		if (!p)
 			goto out_resource;
 		WRITE32(0);
 	}
 	if (bmval0 & FATTR4_WORD0_CASE_PRESERVING) {
-		if ((buflen -= 4) < 0)
+		p = xdr_reserve_space(xdr, 4);
+		if (!p)
 			goto out_resource;
 		WRITE32(1);
 	}
 	if (bmval0 & FATTR4_WORD0_CHOWN_RESTRICTED) {
-		if ((buflen -= 4) < 0)
+		p = xdr_reserve_space(xdr, 4);
+		if (!p)
 			goto out_resource;
 		WRITE32(1);
 	}
 	if (bmval0 & FATTR4_WORD0_FILEHANDLE) {
-		buflen -= (XDR_QUADLEN(fhp->fh_handle.fh_size) << 2) + 4;
-		if (buflen < 0)
+		p = xdr_reserve_space(xdr, fhp->fh_handle.fh_size + 4);
+		if (!p)
 			goto out_resource;
 		WRITE32(fhp->fh_handle.fh_size);
 		WRITEMEM(&fhp->fh_handle.fh_base, fhp->fh_handle.fh_size);
 	}
 	if (bmval0 & FATTR4_WORD0_FILEID) {
-		if ((buflen -= 8) < 0)
+		p = xdr_reserve_space(xdr, 8);
+		if (!p)
 			goto out_resource;
 		WRITE64(stat.ino);
 	}
 	if (bmval0 & FATTR4_WORD0_FILES_AVAIL) {
-		if ((buflen -= 8) < 0)
+		p = xdr_reserve_space(xdr, 8);
+		if (!p)
 			goto out_resource;
 		WRITE64((u64) statfs.f_ffree);
 	}
 	if (bmval0 & FATTR4_WORD0_FILES_FREE) {
-		if ((buflen -= 8) < 0)
+		p = xdr_reserve_space(xdr, 8);
+		if (!p)
 			goto out_resource;
 		WRITE64((u64) statfs.f_ffree);
 	}
 	if (bmval0 & FATTR4_WORD0_FILES_TOTAL) {
-		if ((buflen -= 8) < 0)
+		p = xdr_reserve_space(xdr, 8);
+		if (!p)
 			goto out_resource;
 		WRITE64((u64) statfs.f_files);
 	}
 	if (bmval0 & FATTR4_WORD0_FS_LOCATIONS) {
-		status = nfsd4_encode_fs_locations(rqstp, exp, &p, &buflen);
+		status = nfsd4_encode_fs_locations(xdr, rqstp, exp);
 		if (status)
 			goto out;
 	}
 	if (bmval0 & FATTR4_WORD0_HOMOGENEOUS) {
-		if ((buflen -= 4) < 0)
+		p = xdr_reserve_space(xdr, 4);
+		if (!p)
 			goto out_resource;
 		WRITE32(1);
 	}
 	if (bmval0 & FATTR4_WORD0_MAXFILESIZE) {
-		if ((buflen -= 8) < 0)
+		p = xdr_reserve_space(xdr, 8);
+		if (!p)
 			goto out_resource;
 		WRITE64(exp->ex_path.mnt->mnt_sb->s_maxbytes);
 	}
 	if (bmval0 & FATTR4_WORD0_MAXLINK) {
-		if ((buflen -= 4) < 0)
+		p = xdr_reserve_space(xdr, 4);
+		if (!p)
 			goto out_resource;
 		WRITE32(255);
 	}
 	if (bmval0 & FATTR4_WORD0_MAXNAME) {
-		if ((buflen -= 4) < 0)
+		p = xdr_reserve_space(xdr, 4);
+		if (!p)
 			goto out_resource;
 		WRITE32(statfs.f_namelen);
 	}
 	if (bmval0 & FATTR4_WORD0_MAXREAD) {
-		if ((buflen -= 8) < 0)
+		p = xdr_reserve_space(xdr, 8);
+		if (!p)
 			goto out_resource;
 		WRITE64((u64) svc_max_payload(rqstp));
 	}
 	if (bmval0 & FATTR4_WORD0_MAXWRITE) {
-		if ((buflen -= 8) < 0)
+		p = xdr_reserve_space(xdr, 8);
+		if (!p)
 			goto out_resource;
 		WRITE64((u64) svc_max_payload(rqstp));
 	}
 	if (bmval1 & FATTR4_WORD1_MODE) {
-		if ((buflen -= 4) < 0)
+		p = xdr_reserve_space(xdr, 4);
+		if (!p)
 			goto out_resource;
 		WRITE32(stat.mode & S_IALLUGO);
 	}
 	if (bmval1 & FATTR4_WORD1_NO_TRUNC) {
-		if ((buflen -= 4) < 0)
+		p = xdr_reserve_space(xdr, 4);
+		if (!p)
 			goto out_resource;
 		WRITE32(1);
 	}
 	if (bmval1 & FATTR4_WORD1_NUMLINKS) {
-		if ((buflen -= 4) < 0)
+		p = xdr_reserve_space(xdr, 4);
+		if (!p)
 			goto out_resource;
 		WRITE32(stat.nlink);
 	}
 	if (bmval1 & FATTR4_WORD1_OWNER) {
-		status = nfsd4_encode_user(rqstp, stat.uid, &p, &buflen);
+		status = nfsd4_encode_user(xdr, rqstp, stat.uid);
 		if (status)
 			goto out;
 	}
 	if (bmval1 & FATTR4_WORD1_OWNER_GROUP) {
-		status = nfsd4_encode_group(rqstp, stat.gid, &p, &buflen);
+		status = nfsd4_encode_group(xdr, rqstp, stat.gid);
 		if (status)
 			goto out;
 	}
 	if (bmval1 & FATTR4_WORD1_RAWDEV) {
-		if ((buflen -= 8) < 0)
+		p = xdr_reserve_space(xdr, 8);
+		if (!p)
 			goto out_resource;
 		WRITE32((u32) MAJOR(stat.rdev));
 		WRITE32((u32) MINOR(stat.rdev));
 	}
 	if (bmval1 & FATTR4_WORD1_SPACE_AVAIL) {
-		if ((buflen -= 8) < 0)
+		p = xdr_reserve_space(xdr, 8);
+		if (!p)
 			goto out_resource;
 		dummy64 = (u64)statfs.f_bavail * (u64)statfs.f_bsize;
 		WRITE64(dummy64);
 	}
 	if (bmval1 & FATTR4_WORD1_SPACE_FREE) {
-		if ((buflen -= 8) < 0)
+		p = xdr_reserve_space(xdr, 8);
+		if (!p)
 			goto out_resource;
 		dummy64 = (u64)statfs.f_bfree * (u64)statfs.f_bsize;
 		WRITE64(dummy64);
 	}
 	if (bmval1 & FATTR4_WORD1_SPACE_TOTAL) {
-		if ((buflen -= 8) < 0)
+		p = xdr_reserve_space(xdr, 8);
+		if (!p)
 			goto out_resource;
 		dummy64 = (u64)statfs.f_blocks * (u64)statfs.f_bsize;
 		WRITE64(dummy64);
 	}
 	if (bmval1 & FATTR4_WORD1_SPACE_USED) {
-		if ((buflen -= 8) < 0)
+		p = xdr_reserve_space(xdr, 8);
+		if (!p)
 			goto out_resource;
 		dummy64 = (u64)stat.blocks << 9;
 		WRITE64(dummy64);
 	}
 	if (bmval1 & FATTR4_WORD1_TIME_ACCESS) {
-		if ((buflen -= 12) < 0)
+		p = xdr_reserve_space(xdr, 12);
+		if (!p)
 			goto out_resource;
 		WRITE64((s64)stat.atime.tv_sec);
 		WRITE32(stat.atime.tv_nsec);
 	}
 	if (bmval1 & FATTR4_WORD1_TIME_DELTA) {
-		if ((buflen -= 12) < 0)
+		p = xdr_reserve_space(xdr, 12);
+		if (!p)
 			goto out_resource;
 		WRITE32(0);
 		WRITE32(1);
 		WRITE32(0);
 	}
 	if (bmval1 & FATTR4_WORD1_TIME_METADATA) {
-		if ((buflen -= 12) < 0)
+		p = xdr_reserve_space(xdr, 12);
+		if (!p)
 			goto out_resource;
 		WRITE64((s64)stat.ctime.tv_sec);
 		WRITE32(stat.ctime.tv_nsec);
 	}
 	if (bmval1 & FATTR4_WORD1_TIME_MODIFY) {
-		if ((buflen -= 12) < 0)
+		p = xdr_reserve_space(xdr, 12);
+		if (!p)
 			goto out_resource;
 		WRITE64((s64)stat.mtime.tv_sec);
 		WRITE32(stat.mtime.tv_nsec);
 	}
 	if (bmval1 & FATTR4_WORD1_MOUNTED_ON_FILEID) {
-		if ((buflen -= 8) < 0)
+		p = xdr_reserve_space(xdr, 8);
+		if (!p)
                 	goto out_resource;
 		/*
 		 * Get parent's attributes if not ignoring crossmount
@@ -2475,13 +2520,14 @@ out_acl:
 		WRITE64(stat.ino);
 	}
 	if (bmval2 & FATTR4_WORD2_SECURITY_LABEL) {
-		status = nfsd4_encode_security_label(rqstp, context,
-				contextlen, &p, &buflen);
+		status = nfsd4_encode_security_label(xdr, rqstp, context,
+								contextlen);
 		if (status)
 			goto out;
 	}
 	if (bmval2 & FATTR4_WORD2_SUPPATTR_EXCLCREAT) {
-		if ((buflen -= 16) < 0)
+		p = xdr_reserve_space(xdr, 16);
+		if (!p)
 			goto out_resource;
 		WRITE32(3);
 		WRITE32(NFSD_SUPPATTR_EXCLCREAT_WORD0);
@@ -2489,8 +2535,7 @@ out_acl:
 		WRITE32(NFSD_SUPPATTR_EXCLCREAT_WORD2);
 	}
 
-	*attrlenp = htonl((char *)p - (char *)attrlenp - 4);
-	xdr->p = p;
+	*attrlenp = htonl((char *)xdr->p - (char *)attrlenp - 4);
 	status = nfs_ok;
 
 out:
@@ -2503,6 +2548,13 @@ out:
 		fh_put(tempfh);
 		kfree(tempfh);
 	}
+	if (status) {
+		int nbytes = (char *)xdr->p - (char *)start;
+		/* open code what *should* be xdr_truncate(xdr, len); */
+		xdr->iov->iov_len -= nbytes;
+		xdr->buf->len -= nbytes;
+		xdr->p = start;
+	}
 	return status;
 out_nfserr:
 	status = nfserrno(err);
@@ -2768,13 +2820,10 @@ nfsd4_encode_getattr(struct nfsd4_compoundres *resp, __be32 nfserr, struct nfsd4
 {
 	struct svc_fh *fhp = getattr->ga_fhp;
 	struct xdr_stream *xdr = &resp->xdr;
-	struct xdr_buf *buf = resp->xdr.buf;
 
 	if (nfserr)
 		return nfserr;
 
-	buf->buflen = (void *)resp->xdr.end - (void *)resp->xdr.p
-			- COMPOUND_ERR_SLACK_SPACE;
 	nfserr = nfsd4_encode_fattr(xdr, fhp, fhp->fh_export, fhp->fh_dentry,
 				    getattr->ga_bmval,
 				    resp->rqstp, 0);
@@ -2971,6 +3020,7 @@ nfsd4_encode_read(struct nfsd4_compoundres *resp, __be32 nfserr,
 	int v;
 	struct page *page;
 	unsigned long maxcount; 
+	struct xdr_stream *xdr = &resp->xdr;
 	long len;
 	__be32 *p;
 
@@ -3017,6 +3067,7 @@ nfsd4_encode_read(struct nfsd4_compoundres *resp, __be32 nfserr,
 	resp->xdr.buf->head[0].iov_len = (char *)p
 				- (char *)resp->xdr.buf->head[0].iov_base;
 	resp->xdr.buf->page_len = maxcount;
+	xdr->iov = xdr->buf->tail;
 
 	/* Use rest of head for padding and remaining ops: */
 	resp->xdr.buf->tail[0].iov_base = p;
@@ -3035,6 +3086,7 @@ static __be32
 nfsd4_encode_readlink(struct nfsd4_compoundres *resp, __be32 nfserr, struct nfsd4_readlink *readlink)
 {
 	int maxcount;
+	struct xdr_stream *xdr = &resp->xdr;
 	char *page;
 	__be32 *p;
 
@@ -3067,6 +3119,7 @@ nfsd4_encode_readlink(struct nfsd4_compoundres *resp, __be32 nfserr, struct nfsd
 	resp->xdr.buf->head[0].iov_len = (char *)p
 				- (char *)resp->xdr.buf->head[0].iov_base;
 	resp->xdr.buf->page_len = maxcount;
+	xdr->iov = xdr->buf->tail;
 
 	/* Use rest of head for padding and remaining ops: */
 	resp->xdr.buf->tail[0].iov_base = p;
@@ -3086,6 +3139,7 @@ nfsd4_encode_readdir(struct nfsd4_compoundres *resp, __be32 nfserr, struct nfsd4
 {
 	int maxcount;
 	loff_t offset;
+	struct xdr_stream *xdr = &resp->xdr;
 	__be32 *page, *savep, *tailbase;
 	__be32 *p;
 
@@ -3148,6 +3202,8 @@ nfsd4_encode_readdir(struct nfsd4_compoundres *resp, __be32 nfserr, struct nfsd4
 	resp->xdr.buf->page_len = ((char *)p) -
 		(char*)page_address(*(resp->rqstp->rq_next_page-1));
 
+	xdr->iov = xdr->buf->tail;
+
 	/* Use rest of head for padding and remaining ops: */
 	resp->xdr.buf->tail[0].iov_base = tailbase;
 	resp->xdr.buf->tail[0].iov_len = 0;