More progress on parsing elf files. Fixes to memfs file read/write

Increased inode block pointers to 40. The current maximum allowed (and checked).
Updates to file size after every file write ensures subsequent writes can
correctly operate using updated file size information (i.e. not try to add
more pages that are already present). We cannot do this inside write() because
directory writes rely on byte-granularity updates on file buffers, whereas
file updates are by page-granularity (currently).

tasks/mm0/include/exec.h

@@ -13,6 +13,7 @@
 struct exec_file_desc {
 	unsigned long text_offset;	/* File offset of text section */
 	unsigned long data_offset;	/* File offset of data section */
+	unsigned long bss_offset;	/* File offset of bss section */
 };
 
 #endif /* __EXEC_H__ */

tasks/mm0/include/lib/elf/elf.h

@@ -58,4 +58,7 @@ struct elf_header {
 } __attribute__((__packed__));
 
 
+int elf_parse_executable(struct tcb *task, struct vm_file *file,
+			 struct exec_file_desc *efd);
+
 #endif /* __ELF_H__ */