Throw const on some strings

In C, const indicates to the reader that mutation will not occur.
It can also serve as a hint about ownership.

Add const in a few places where it makes sense.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Ryan Moeller <freqlabs@FreeBSD.org>
Closes #10997

module/os/linux/zfs/zfs_ctldir.c

@@ -131,7 +131,7 @@ static void zfsctl_snapshot_unmount_delay_impl(zfs_snapentry_t *se, int delay);
  * the snapshot name and provided mount point.  No reference is taken.
  */
 static zfs_snapentry_t *
-zfsctl_snapshot_alloc(char *full_name, char *full_path, spa_t *spa,
+zfsctl_snapshot_alloc(const char *full_name, const char *full_path, spa_t *spa,
     uint64_t objsetid, struct dentry *root_dentry)
 {
 	zfs_snapentry_t *se;
@@ -261,13 +261,13 @@ snapentry_compare_by_objsetid(const void *a, const void *b)
  * NULL will be returned.
  */
 static zfs_snapentry_t *
-zfsctl_snapshot_find_by_name(char *snapname)
+zfsctl_snapshot_find_by_name(const char *snapname)
 {
 	zfs_snapentry_t *se, search;
 
 	ASSERT(RW_LOCK_HELD(&zfs_snapshot_lock));
 
-	search.se_name = snapname;
+	search.se_name = (char *)snapname;
 	se = avl_find(&zfs_snapshots_by_name, &search, NULL);
 	if (se)
 		zfsctl_snapshot_hold(se);
@@ -301,7 +301,7 @@ zfsctl_snapshot_find_by_objsetid(spa_t *spa, uint64_t objsetid)
  * removed, renamed, and added back to the new correct location in the tree.
  */
 static int
-zfsctl_snapshot_rename(char *old_snapname, char *new_snapname)
+zfsctl_snapshot_rename(const char *old_snapname, const char *new_snapname)
 {
 	zfs_snapentry_t *se;
 
@@ -410,7 +410,7 @@ zfsctl_snapshot_unmount_delay(spa_t *spa, uint64_t objsetid, int delay)
  * and zero when unmounted.
  */
 static boolean_t
-zfsctl_snapshot_ismounted(char *snapname)
+zfsctl_snapshot_ismounted(const char *snapname)
 {
 	zfs_snapentry_t *se;
 	boolean_t ismounted = B_FALSE;
@@ -751,7 +751,7 @@ out:
  * Special case the handling of "..".
  */
 int
-zfsctl_root_lookup(struct inode *dip, char *name, struct inode **ipp,
+zfsctl_root_lookup(struct inode *dip, const char *name, struct inode **ipp,
     int flags, cred_t *cr, int *direntflags, pathname_t *realpnp)
 {
 	zfsvfs_t *zfsvfs = ITOZSB(dip);
@@ -784,7 +784,7 @@ zfsctl_root_lookup(struct inode *dip, char *name, struct inode **ipp,
  * snapshot if it exist, creating the pseudo filesystem inode as necessary.
  */
 int
-zfsctl_snapdir_lookup(struct inode *dip, char *name, struct inode **ipp,
+zfsctl_snapdir_lookup(struct inode *dip, const char *name, struct inode **ipp,
     int flags, cred_t *cr, int *direntflags, pathname_t *realpnp)
 {
 	zfsvfs_t *zfsvfs = ITOZSB(dip);
@@ -815,8 +815,8 @@ zfsctl_snapdir_lookup(struct inode *dip, char *name, struct inode **ipp,
  * to the '.zfs/snapshot' directory snapshots cannot be moved elsewhere.
  */
 int
-zfsctl_snapdir_rename(struct inode *sdip, char *snm,
-    struct inode *tdip, char *tnm, cred_t *cr, int flags)
+zfsctl_snapdir_rename(struct inode *sdip, const char *snm,
+    struct inode *tdip, const char *tnm, cred_t *cr, int flags)
 {
 	zfsvfs_t *zfsvfs = ITOZSB(sdip);
 	char *to, *from, *real, *fsname;
@@ -893,7 +893,8 @@ out:
  * the removal of the snapshot with the given name.
  */
 int
-zfsctl_snapdir_remove(struct inode *dip, char *name, cred_t *cr, int flags)
+zfsctl_snapdir_remove(struct inode *dip, const char *name, cred_t *cr,
+    int flags)
 {
 	zfsvfs_t *zfsvfs = ITOZSB(dip);
 	char *snapname, *real;
@@ -941,7 +942,7 @@ out:
  * the creation of a new snapshot with the given name.
  */
 int
-zfsctl_snapdir_mkdir(struct inode *dip, char *dirname, vattr_t *vap,
+zfsctl_snapdir_mkdir(struct inode *dip, const char *dirname, vattr_t *vap,
     struct inode **ipp, cred_t *cr, int flags)
 {
 	zfsvfs_t *zfsvfs = ITOZSB(dip);
@@ -1001,7 +1002,7 @@ exportfs_flush(void)
  * it's in use, the unmount will fail harmlessly.
  */
 int
-zfsctl_snapshot_unmount(char *snapname, int flags)
+zfsctl_snapshot_unmount(const char *snapname, int flags)
 {
 	char *argv[] = { "/usr/bin/env", "umount", "-t", "zfs", "-n", NULL,
 	    NULL };

module/os/linux/zfs/zfs_dir.c

@@ -60,8 +60,9 @@
  * of names after deciding which is the appropriate lookup interface.
  */
 static int
-zfs_match_find(zfsvfs_t *zfsvfs, znode_t *dzp, char *name, matchtype_t mt,
-    boolean_t update, int *deflags, pathname_t *rpnp, uint64_t *zoid)
+zfs_match_find(zfsvfs_t *zfsvfs, znode_t *dzp, const char *name,
+    matchtype_t mt, boolean_t update, int *deflags, pathname_t *rpnp,
+    uint64_t *zoid)
 {
 	boolean_t conflict = B_FALSE;
 	int error;
@@ -139,8 +140,8 @@ zfs_match_find(zfsvfs_t *zfsvfs, znode_t *dzp, char *name, matchtype_t mt,
  *	 but return znode pointers to a single match.
  */
 int
-zfs_dirent_lock(zfs_dirlock_t **dlpp, znode_t *dzp, char *name, znode_t **zpp,
-    int flag, int *direntflags, pathname_t *realpnp)
+zfs_dirent_lock(zfs_dirlock_t **dlpp, znode_t *dzp, char *name,
+    znode_t **zpp, int flag, int *direntflags, pathname_t *realpnp)
 {
 	zfsvfs_t	*zfsvfs = ZTOZSB(dzp);
 	zfs_dirlock_t	*dl;

module/os/linux/zfs/zfs_vnops.c

@@ -1234,8 +1234,8 @@ zfs_access(struct inode *ip, int mode, int flag, cred_t *cr)
  */
 /* ARGSUSED */
 int
-zfs_lookup(znode_t *zdp, char *nm, znode_t **zpp, int flags,
-    cred_t *cr, int *direntflags, pathname_t *realpnp)
+zfs_lookup(znode_t *zdp, char *nm, znode_t **zpp, int flags, cred_t *cr,
+    int *direntflags, pathname_t *realpnp)
 {
 	zfsvfs_t *zfsvfs = ZTOZSB(zdp);
 	int error = 0;