NFSD: Refactor the generic write vector fill helper

fill_in_write_vector() is nearly the same logic as
svc_fill_write_vector(), but there are a few differences so that
the former can handle multiple WRITE payloads in a single COMPOUND.

svc_fill_write_vector() can be adjusted so that it can be used in
the NFSv4 WRITE code path too. Instead of assuming the pages are
coming from rq_args.pages, have the caller pass in the page list.

The immediate benefit is a reduction of code duplication. It also
prevents the NFSv4 WRITE decoder from passing an empty vector
element when the transport has provided the payload in the xdr_buf's
page array.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
diff --git a/fs/nfsd/nfs3proc.c b/fs/nfsd/nfs3proc.c
index 6259a4b..8d1c2d1a 100644
--- a/fs/nfsd/nfs3proc.c
+++ b/fs/nfsd/nfs3proc.c
@@ -202,7 +202,8 @@ nfsd3_proc_write(struct svc_rqst *rqstp)
 
 	fh_copy(&resp->fh, &argp->fh);
 	resp->committed = argp->stable;
-	nvecs = svc_fill_write_vector(rqstp, &argp->first, cnt);
+	nvecs = svc_fill_write_vector(rqstp, rqstp->rq_arg.pages,
+				      &argp->first, cnt);
 	if (!nvecs)
 		RETURN_STATUS(nfserr_io);
 	nfserr = nfsd_write(rqstp, &resp->fh, argp->offset,
diff --git a/fs/nfsd/nfs4proc.c b/fs/nfsd/nfs4proc.c
index 3652f9b..b7bc6e1 100644
--- a/fs/nfsd/nfs4proc.c
+++ b/fs/nfsd/nfs4proc.c
@@ -986,24 +986,6 @@ nfsd4_setattr(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
 	return status;
 }
 
-static int fill_in_write_vector(struct kvec *vec, struct nfsd4_write *write)
-{
-        int i = 1;
-        int buflen = write->wr_buflen;
-
-        vec[0].iov_base = write->wr_head.iov_base;
-        vec[0].iov_len = min_t(int, buflen, write->wr_head.iov_len);
-        buflen -= vec[0].iov_len;
-
-        while (buflen) {
-                vec[i].iov_base = page_address(write->wr_pagelist[i - 1]);
-                vec[i].iov_len = min_t(int, PAGE_SIZE, buflen);
-                buflen -= vec[i].iov_len;
-                i++;
-        }
-        return i;
-}
-
 static __be32
 nfsd4_write(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
 	    union nfsd4_op_u *u)
@@ -1031,7 +1013,10 @@ nfsd4_write(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
 	write->wr_how_written = write->wr_stable_how;
 	gen_boot_verifier(&write->wr_verifier, SVC_NET(rqstp));
 
-	nvecs = fill_in_write_vector(rqstp->rq_vec, write);
+	nvecs = svc_fill_write_vector(rqstp, write->wr_pagelist,
+				      &write->wr_head, write->wr_buflen);
+	if (!nvecs)
+		return nfserr_io;
 	WARN_ON_ONCE(nvecs > ARRAY_SIZE(rqstp->rq_vec));
 
 	status = nfsd_vfs_write(rqstp, &cstate->current_fh, filp,
diff --git a/fs/nfsd/nfsproc.c b/fs/nfsd/nfsproc.c
index f107f9f..a6faee5 100644
--- a/fs/nfsd/nfsproc.c
+++ b/fs/nfsd/nfsproc.c
@@ -218,7 +218,8 @@ nfsd_proc_write(struct svc_rqst *rqstp)
 		SVCFH_fmt(&argp->fh),
 		argp->len, argp->offset);
 
-	nvecs = svc_fill_write_vector(rqstp, &argp->first, cnt);
+	nvecs = svc_fill_write_vector(rqstp, rqstp->rq_arg.pages,
+				      &argp->first, cnt);
 	if (!nvecs)
 		return nfserr_io;
 	nfserr = nfsd_write(rqstp, fh_copy(&resp->fh, &argp->fh),