9p: Make use of iounit for read/write

Change the v9fs_file_readn function to limit the maximum transfer size
based on the iounit or msize.

Also remove the redundant check for limiting the transfer size in
v9fs_file_write. This check is done by p9_client_write.
Signed-off-by: NM. Mohan Kumar <mohan@in.ibm.com>
Signed-off-by: NEric Van Hensbergen <ericvh@gmail.com>

fs/9p/vfs_file.c

@@ -139,7 +139,7 @@ ssize_t
 v9fs_file_readn(struct file *filp, char *data, char __user *udata, u32 count,
 	       u64 offset)
 {
-	int n, total;
+	int n, total, size;
 	struct p9_fid *fid = filp->private_data;
 
 	P9_DPRINTK(P9_DEBUG_VFS, "fid %d offset %llu count %d\n", fid->fid,
@@ -147,6 +147,7 @@ v9fs_file_readn(struct file *filp, char *data, char __user *udata, u32 count,
 
 	n = 0;
 	total = 0;
+	size = fid->iounit ? fid->iounit : fid->clnt->msize - P9_IOHDRSZ;
 	do {
 		n = p9_client_read(fid, data, udata, offset, count);
 		if (n <= 0)
@@ -160,7 +161,7 @@ v9fs_file_readn(struct file *filp, char *data, char __user *udata, u32 count,
 		offset += n;
 		count -= n;
 		total += n;
-	} while (count > 0 && n == (fid->clnt->msize - P9_IOHDRSZ));
+	} while (count > 0 && n == size);
 
 	if (n < 0)
 		total = n;
@@ -183,11 +184,13 @@ v9fs_file_read(struct file *filp, char __user *udata, size_t count,
 {
 	int ret;
 	struct p9_fid *fid;
+	size_t size;
 
 	P9_DPRINTK(P9_DEBUG_VFS, "count %zu offset %lld\n", count, *offset);
 	fid = filp->private_data;
 
-	if (count > (fid->clnt->msize - P9_IOHDRSZ))
+	size = fid->iounit ? fid->iounit : fid->clnt->msize - P9_IOHDRSZ;
+	if (count > size)
 		ret = v9fs_file_readn(filp, NULL, udata, count, *offset);
 	else
 		ret = p9_client_read(fid, NULL, udata, *offset, count);
@@ -224,9 +227,7 @@ v9fs_file_write(struct file *filp, const char __user * data,
 	fid = filp->private_data;
 	clnt = fid->clnt;
 
-	rsize = fid->iounit;
-	if (!rsize || rsize > clnt->msize-P9_IOHDRSZ)
-		rsize = clnt->msize - P9_IOHDRSZ;
+	rsize = fid->iounit ? fid->iounit : clnt->msize - P9_IOHDRSZ;
 
 	do {
 		if (count < rsize)