btrfs-progs: add helper for copying paths

Check the source path length and do the copy.

Signed-off-by: David Sterba <dsterba@suse.cz>

utils.c

@@ -2871,3 +2871,22 @@ int btrfs_check_nodesize(u32 nodesize, u32 sectorsize)
 	}
 	return 0;
 }
+
+/*
+ * Copy a path argument from SRC to DEST and check the SRC length if it's at
+ * most PATH_MAX and fits into DEST. DESTLEN is supposed to be exact size of
+ * the buffer.
+ * The destination buffer is zero terminated.
+ * Return < 0 for error, 0 otherwise.
+ */
+int arg_copy_path(char *dest, const char *src, int destlen)
+{
+	size_t len = strlen(src);
+
+	if (len >= PATH_MAX || len >= destlen)
+		return -ENAMETOOLONG;
+
+	__strncpy__null(dest, src, destlen);
+
+	return 0;
+}

utils.h

@@ -135,6 +135,7 @@ int get_mountpt(char *dev, char *mntpt, size_t size);
 u64 parse_size(char *s);
 u64 parse_qgroupid(const char *p);
 u64 arg_strtou64(const char *str);
+int arg_copy_path(char *dest, const char *src, int destlen);
 int open_file_or_dir(const char *fname, DIR **dirstream);
 int open_file_or_dir3(const char *fname, DIR **dirstream, int open_flags);
 void close_file_or_dir(int fd, DIR *dirstream);