zdump: refactor pt_load_add

In an upcoming patch the refactored function `pt_load_add` is reused. While at
it, add a wrap-around check to `pt_load_add`, replace `g.opts.device` access
with `fh->path` (this makes this function easier testable) and improve the
documentation.

Signed-off-by: Marc Hartmayer <mhartmay@linux.ibm.com>
Reviewed-by: Steffen Eiden <seiden@linux.ibm.com>
Signed-off-by: Jan Höppner <hoeppner@linux.ibm.com>

zdump/dfi_elf_common.h

@@ -0,0 +1,36 @@
+/*
+ * zgetdump - Tool for copying and converting System z dumps
+ *
+ * Common ELF core dump input format definitions
+ *
+ * Copyright IBM Corp. 2001, 2022
+ *
+ * s390-tools is free software; you can redistribute it and/or modify
+ * it under the terms of the MIT license. See LICENSE for details.
+ */
+
+#ifndef DFI_ELF_COMMON_H
+#define DFI_ELF_COMMON_H
+
+#include <elf.h>
+
+#include "dfi_mem_chunk.h"
+#include "zg.h"
+
+/**
+ * pt_load_add:
+ * @fh: (not nullable): open input file
+ * @phdr: (not nullable): program ELF header of the load segment to add
+ * @data: (not nullable): arbitrary pointer passed to the read callback @read_fn
+ * @read_fn: (not nullable): callback used for reading the data of a memory chunk
+ * @free_fn: (not nullable): function called to cleanup @data
+ *
+ * Add load (memory chunk) to DFI dump. After a successful call, @data belongs
+ * to the mem_chunk structure created and the @data pointer is set to %NULL.
+ *
+ * Returns: %0 on success, returns < 0 in case of an error
+ */
+int pt_load_add(const struct zg_fh *fh, const Elf64_Phdr *phdr, void **data,
+		dfi_mem_chunk_read_fn read_fn, dfi_mem_chunk_free_fn free_fn);
+
+#endif /* DFI_ELF_COMMON_H */