From: Jason Gunthorpe <jgg@mellanox.com>
Date: Wed, 24 Jan 2018 19:58:34 -0700
Subject: RDMA/uverbs: Use an unambiguous errno for method not supported
Patch-mainline: v4.16-rc1
Git-commit: 3624a8f02568f08aef299d3b117f2226f621177d
References: bsc#1046306 FATE#322942

Returning EOPNOTSUPP is problematic because it can also be
returned by the method function, and we use it in quite a few
places in drivers these days.

Instead, dedicate EPROTONOSUPPORT to indicate that the ioctl framework
is enabled but the requested object and method are not supported by
the kernel. No other case will return this code, and it lets userspace
know to fall back to write().

grep says we do not use it today in drivers/infiniband subsystem.

Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>
Reviewed-by: Matan Barak <matanb@mellanox.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>
Acked-by: Thomas Bogendoerfer <tbogendoerfer@suse.de>
---
 drivers/infiniband/core/uverbs_ioctl.c |   19 +++++++++++++------
 1 file changed, 13 insertions(+), 6 deletions(-)

--- a/drivers/infiniband/core/uverbs_ioctl.c
+++ b/drivers/infiniband/core/uverbs_ioctl.c
@@ -243,16 +243,13 @@ static long ib_uverbs_cmd_verbs(struct i
 	size_t ctx_size;
 	uintptr_t data[UVERBS_OPTIMIZE_USING_STACK_SZ / sizeof(uintptr_t)];
 
-	if (hdr->reserved)
-		return -EINVAL;
-
 	object_spec = uverbs_get_object(ib_dev, hdr->object_id);
 	if (!object_spec)
-		return -EOPNOTSUPP;
+		return -EPROTONOSUPPORT;
 
 	method_spec = uverbs_get_method(object_spec, hdr->method_id);
 	if (!method_spec)
-		return -EOPNOTSUPP;
+		return -EPROTONOSUPPORT;
 
 	if ((method_spec->flags & UVERBS_ACTION_FLAG_CREATE_ROOT) ^ !file->ucontext)
 		return -EINVAL;
@@ -305,6 +302,16 @@ static long ib_uverbs_cmd_verbs(struct i
 
 	err = uverbs_handle_method(buf, ctx->uattrs, hdr->num_attrs, ib_dev,
 				   file, method_spec, ctx->uverbs_attr_bundle);
+
+	/*
+	 * EPROTONOSUPPORT is ONLY to be returned if the ioctl framework can
+	 * not invoke the method because the request is not supported.  No
+	 * other cases should return this code.
+	*/
+	if (unlikely(err == -EPROTONOSUPPORT)) {
+		WARN_ON_ONCE(err == -EPROTONOSUPPORT);
+		err = -EINVAL;
+	}
 out:
 	if (ctx != (void *)data)
 		kfree(ctx);
@@ -341,7 +348,7 @@ long ib_uverbs_ioctl(struct file *filp,
 		}
 
 		if (hdr.reserved) {
-			err = -EOPNOTSUPP;
+			err = -EPROTONOSUPPORT;
 			goto out;
 		}