bitfield.h: add FIELD_FIT() helper

Add a helper for checking at runtime that a value will fit inside
a specified field/mask.

Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 13 insertions, 0 deletions

diff --git a/include/linux/bitfield.h b/include/linux/bitfield.h
index f6505d83069d..8b9d6fff002d 100644
--- a/include/linux/bitfield.h
+++ b/include/linux/bitfield.h
@@ -63,6 +63,19 @@
 	})
 
 /**
+ * FIELD_FIT() - check if value fits in the field
+ * @_mask: shifted mask defining the field's length and position
+ * @_val:  value to test against the field
+ *
+ * Return: true if @_val can fit inside @_mask, false if @_val is too big.
+ */
+#define FIELD_FIT(_mask, _val)						\
+	({								\
+		__BF_FIELD_CHECK(_mask, 0ULL, _val, "FIELD_FIT: ");	\
+		!((((typeof(_mask))_val) << __bf_shf(_mask)) & ~(_mask)); \
+	})
+
+/**
  * FIELD_PREP() - prepare a bitfield element
  * @_mask: shifted mask defining the field's length and position
  * @_val:  value to put in the field