Constify some rrd_*() functions

These don't modify the db, so just constify them while we're in the
area.

Reviewed-by: Alexander Motin <[email protected]>
Reviewed-by: Brian Behlendorf <[email protected]>
Reviewed-by: Chris Longros <[email protected]>
Signed-off-by: Kyle Evans <[email protected]>
Closes #18645

include/zfs_crrd.h

@@ -60,12 +60,12 @@ typedef struct {
 	rrd_t		dbr_months;
 } dbrrd_t;
 
-size_t rrd_len(rrd_t *rrd);
+size_t rrd_len(const rrd_t *rrd);
 
-const rrd_data_t *rrd_entry(rrd_t *r, size_t i);
+const rrd_data_t *rrd_entry(const rrd_t *r, size_t i);
 rrd_data_t *rrd_tail_entry(rrd_t *rrd);
 uint64_t rrd_tail(rrd_t *rrd);
-uint64_t rrd_get(rrd_t *rrd, size_t i);
+uint64_t rrd_get(const rrd_t *rrd, size_t i);
 
 void rrd_add(rrd_t *rrd, hrtime_t time, uint64_t txg);
 

module/zfs/zfs_crrd.c

@@ -99,14 +99,14 @@ rrd_tail(rrd_t *rrd)
  * rrd_get works from 0..rrd_len()-1.
  */
 size_t
-rrd_len(rrd_t *rrd)
+rrd_len(const rrd_t *rrd)
 {
 
 	return (rrd->rrd_length);
 }
 
 const rrd_data_t *
-rrd_entry(rrd_t *rrd, size_t i)
+rrd_entry(const rrd_t *rrd, size_t i)
 {
 	size_t n;
 
@@ -119,7 +119,7 @@ rrd_entry(rrd_t *rrd, size_t i)
 }
 
 uint64_t
-rrd_get(rrd_t *rrd, size_t i)
+rrd_get(const rrd_t *rrd, size_t i)
 {
 	const rrd_data_t *data = rrd_entry(rrd, i);