nfsd: split off the write decode code into a separate function

nfs4_decode_write has code to parse incoming XDR write data in to
a kvec head, and a list of pages.

Put this code in to a separate function, so that it can be used
later by the xattr code, for setxattr. No functional change.
Signed-off-by: Frank van der Linden <fllinden@amazon.com>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

fs/nfsd/nfs4xdr.c

@@ -257,6 +257,44 @@ svcxdr_dupstr(struct nfsd4_compoundargs *argp, void *buf, u32 len)
 	return p;
 }
 
+static __be32
+svcxdr_construct_vector(struct nfsd4_compoundargs *argp, struct kvec *head,
+			struct page ***pagelist, u32 buflen)
+{
+	int avail;
+	int len;
+	int pages;
+
+	/* Sorry .. no magic macros for this.. *
+	 * READ_BUF(write->wr_buflen);
+	 * SAVEMEM(write->wr_buf, write->wr_buflen);
+	 */
+	avail = (char *)argp->end - (char *)argp->p;
+	if (avail + argp->pagelen < buflen) {
+		dprintk("NFSD: xdr error (%s:%d)\n",
+			       __FILE__, __LINE__);
+		return nfserr_bad_xdr;
+	}
+	head->iov_base = argp->p;
+	head->iov_len = avail;
+	*pagelist = argp->pagelist;
+
+	len = XDR_QUADLEN(buflen) << 2;
+	if (len >= avail) {
+		len -= avail;
+
+		pages = len >> PAGE_SHIFT;
+		argp->pagelist += pages;
+		argp->pagelen -= pages * PAGE_SIZE;
+		len -= pages * PAGE_SIZE;
+
+		next_decode_page(argp);
+	}
+	argp->p += XDR_QUADLEN(len);
+
+	return 0;
+}
+
 /**
  * savemem - duplicate a chunk of memory for later processing
  * @argp: NFSv4 compound argument structure to be freed with
@@ -1265,8 +1303,6 @@ nfsd4_decode_verify(struct nfsd4_compoundargs *argp, struct nfsd4_verify *verify
 static __be32
 nfsd4_decode_write(struct nfsd4_compoundargs *argp, struct nfsd4_write *write)
 {
-	int avail;
-	int len;
 	DECODE_HEAD;
 
 	status = nfsd4_decode_stateid(argp, &write->wr_stateid);
@@ -1279,34 +1315,10 @@ nfsd4_decode_write(struct nfsd4_compoundargs *argp, struct nfsd4_write *write)
 		goto xdr_error;
 	write->wr_buflen = be32_to_cpup(p++);
 
-	/* Sorry .. no magic macros for this.. *
-	 * READ_BUF(write->wr_buflen);
-	 * SAVEMEM(write->wr_buf, write->wr_buflen);
-	 */
-	avail = (char*)argp->end - (char*)argp->p;
-	if (avail + argp->pagelen < write->wr_buflen) {
-		dprintk("NFSD: xdr error (%s:%d)\n",
-				__FILE__, __LINE__);
-		goto xdr_error;
-	}
-	write->wr_head.iov_base = p;
-	write->wr_head.iov_len = avail;
-	write->wr_pagelist = argp->pagelist;
-
-	len = XDR_QUADLEN(write->wr_buflen) << 2;
-	if (len >= avail) {
-		int pages;
-
-		len -= avail;
-
-		pages = len >> PAGE_SHIFT;
-		argp->pagelist += pages;
-		argp->pagelen -= pages * PAGE_SIZE;
-		len -= pages * PAGE_SIZE;
-
-		next_decode_page(argp);
-	}
-	argp->p += XDR_QUADLEN(len);
+	status = svcxdr_construct_vector(argp, &write->wr_head,
+					 &write->wr_pagelist, write->wr_buflen);
+	if (status)
+		return status;
 
 	DECODE_TAIL;
 }