1@findex struct bfd_iovec
2@subsubsection @code{struct bfd_iovec}
3@strong{Description}@*
4The @code{struct bfd_iovec} contains the internal file I/O class.
5Each @code{BFD} has an instance of this class and all file I/O is
6routed through it (it is assumed that the instance implements
7all methods listed below).
8@example
9struct bfd_iovec
10@{
11  /* To avoid problems with macros, a "b" rather than "f"
12     prefix is prepended to each method name.  */
13  /* Attempt to read/write NBYTES on ABFD's IOSTREAM storing/fetching
14     bytes starting at PTR.  Return the number of bytes actually
15     transfered (a read past end-of-file returns less than NBYTES),
16     or -1 (setting @code{bfd_error}) if an error occurs.  */
17  file_ptr (*bread) (struct bfd *abfd, void *ptr, file_ptr nbytes);
18  file_ptr (*bwrite) (struct bfd *abfd, const void *ptr,
19                      file_ptr nbytes);
20  /* Return the current IOSTREAM file offset, or -1 (setting @code{bfd_error}
21     if an error occurs.  */
22  file_ptr (*btell) (struct bfd *abfd);
23  /* For the following, on successful completion a value of 0 is returned.
24     Otherwise, a value of -1 is returned (and  @code{bfd_error} is set).  */
25  int (*bseek) (struct bfd *abfd, file_ptr offset, int whence);
26  int (*bclose) (struct bfd *abfd);
27  int (*bflush) (struct bfd *abfd);
28  int (*bstat) (struct bfd *abfd, struct stat *sb);
29@};
30@end example
31
32@findex bfd_get_mtime
33@subsubsection @code{bfd_get_mtime}
34@strong{Synopsis}
35@example
36long bfd_get_mtime (bfd *abfd);
37@end example
38@strong{Description}@*
39Return the file modification time (as read from the file system, or
40from the archive header for archive members).
41
42@findex bfd_get_size
43@subsubsection @code{bfd_get_size}
44@strong{Synopsis}
45@example
46file_ptr bfd_get_size (bfd *abfd);
47@end example
48@strong{Description}@*
49Return the file size (as read from file system) for the file
50associated with BFD @var{abfd}.
51
52The initial motivation for, and use of, this routine is not
53so we can get the exact size of the object the BFD applies to, since
54that might not be generally possible (archive members for example).
55It would be ideal if someone could eventually modify
56it so that such results were guaranteed.
57
58Instead, we want to ask questions like "is this NNN byte sized
59object I'm about to try read from file offset YYY reasonable?"
60As as example of where we might do this, some object formats
61use string tables for which the first @code{sizeof (long)} bytes of the
62table contain the size of the table itself, including the size bytes.
63If an application tries to read what it thinks is one of these
64string tables, without some way to validate the size, and for
65some reason the size is wrong (byte swapping error, wrong location
66for the string table, etc.), the only clue is likely to be a read
67error when it tries to read the table, or a "virtual memory
68exhausted" error when it tries to allocate 15 bazillon bytes
69of space for the 15 bazillon byte table it is about to read.
70This function at least allows us to answer the question, "is the
71size reasonable?".
72
73