NFSD: Use vfs_iocb_iter_read()

Refactor: Enable the use of IOCB flags to control NFSD's individual
read operations (when not using splice). This allows the eventual
use of atomic, uncached, direct, or asynchronous reads.

Suggested-by: Christoph Hellwig <hch@infradead.org>
Reviewed-by: NeilBrown <neil@brown.name>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

Author: chucklever

fs/nfsd/vfs.c

@@ -1086,10 +1086,13 @@ __be32 nfsd_iter_read(struct svc_rqst *rqstp, struct svc_fh *fhp,
 {
 	unsigned long v, total;
 	struct iov_iter iter;
-	loff_t ppos = offset;
+	struct kiocb kiocb;
 	ssize_t host_err;
 	size_t len;
 
+	init_sync_kiocb(&kiocb, file);
+	kiocb.ki_pos = offset;
+
 	v = 0;
 	total = *count;
 	while (total) {
@@ -1104,7 +1107,7 @@ __be32 nfsd_iter_read(struct svc_rqst *rqstp, struct svc_fh *fhp,
 
 	trace_nfsd_read_vector(rqstp, fhp, offset, *count);
 	iov_iter_bvec(&iter, ITER_DEST, rqstp->rq_bvec, v, *count);
-	host_err = vfs_iter_read(file, &iter, &ppos, 0);
+	host_err = vfs_iocb_iter_read(file, &kiocb, &iter);
 	return nfsd_finish_read(rqstp, fhp, file, offset, count, eof, host_err);
 }