debugfs: Use the hash_version from superblock if a file system is opened

The debugfs program's dx_hash command computes the hash for the given
filename, taking the hash_seed and hash_version (i.e hash algorithm)
as arguments.  So the user has to refer to the superblock to get these
values used by the filesystem.  So if debugfs has an opened file
system, use those values from the current file system.

[ Fixed patch to avoid crashing when a file system is not opened. --TYT ]

Signed-off-by: Srivathsa Dara <srivathsa.d.dara@oracle.com>
Link: https://lore.kernel.org/r/20230824065634.2662858-1-srivathsa.d.dara@oracle.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

Author: srivathsa729

debugfs/htree.c

@@ -336,11 +336,18 @@ void do_dx_hash(int argc, char *argv[], int sci_idx EXT2FS_ATTR((unused)),
 	errcode_t	err;
 	int		c;
 	int		hash_version = 0;
-	__u32		hash_seed[4];
+	__u32		hash_seed[4] = { 0, };
 	int		hash_flags = 0;
 	const struct ext2fs_nls_table *encoding = NULL;
 
-	hash_seed[0] = hash_seed[1] = hash_seed[2] = hash_seed[3] = 0;
+	if (current_fs) {
+		hash_seed[0] = current_fs->super->s_hash_seed[0];
+		hash_seed[1] = current_fs->super->s_hash_seed[1];
+		hash_seed[2] = current_fs->super->s_hash_seed[2];
+		hash_seed[3] = current_fs->super->s_hash_seed[3];
+
+		hash_version = current_fs->super->s_def_hash_version;
+	}
 
 	reset_getopt();
 	while ((c = getopt(argc, argv, "h:s:ce:")) != EOF) {