RDMA/uverbs: Add UVERBS_ATTR_CONST_IN to the specs language

This makes it clear and safe to access constants passed in from user
space. We define a consistent ABI of u64 for all constants, and verify
that the data passed in can be represented by the type the user supplies.

The expectation is this will always be used with an enum declaring the
constant values, and the user will use the enum type as input to the
accessor.

To retrieve the attribute value we introduce two helper calls - one
standard which may fail if attribute is not valid and one where caller can
provide a default value which will be used in case the attribute is not
valid (useful when attribute is optional).

Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>
Signed-off-by: Ariel Levkovich <lariel@mellanox.com>
Signed-off-by: Mark Bloch <markb@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>

1 files changed, 23 insertions, 0 deletions

diff --git a/drivers/infiniband/core/uverbs_ioctl.c b/drivers/infiniband/core/uverbs_ioctl.c
index 1a6b229e3db3..4bafd4671de2 100644
--- a/drivers/infiniband/core/uverbs_ioctl.c
+++ b/drivers/infiniband/core/uverbs_ioctl.c
@@ -611,3 +611,26 @@ int uverbs_copy_to(const struct uverbs_attr_bundle *bundle, size_t idx,
 	return 0;
 }
 EXPORT_SYMBOL(uverbs_copy_to);
+
+int _uverbs_get_const(s64 *to, const struct uverbs_attr_bundle *attrs_bundle,
+		      size_t idx, s64 lower_bound, u64 upper_bound,
+		      s64  *def_val)
+{
+	const struct uverbs_attr *attr;
+
+	attr = uverbs_attr_get(attrs_bundle, idx);
+	if (IS_ERR(attr)) {
+		if ((PTR_ERR(attr) != -ENOENT) || !def_val)
+			return PTR_ERR(attr);
+
+		*to = *def_val;
+	} else {
+		*to = attr->ptr_attr.data;
+	}
+
+	if (*to < lower_bound || (*to > 0 && (u64)*to > upper_bound))
+		return -EINVAL;
+
+	return 0;
+}
+EXPORT_SYMBOL(_uverbs_get_const);