2006-11-28 Miguel de Icaza <miguel@novell.com>
[mono-project.git] / support / errno.c
blob26ee780169183aff8538e23987818f38721356f4
1 /*
2 * <errno.h> wrapper functions.
3 */
5 #include <errno.h>
6 #include <string.h>
7 #include "map.h"
8 #include "mph.h"
9 #include <stdio.h>
11 G_BEGIN_DECLS
13 void
14 Mono_Posix_Stdlib_SetLastError (int error_number)
16 errno = error_number;
19 #ifdef HAVE_STRERROR_R
21 /*
22 * There are two versions of strerror_r:
23 * - the GNU version: char *strerror_r (int errnum, char *buf, size_t n);
24 * - the XPG version: int strerror_r (int errnum, char *buf, size_t n);
26 * Ideally I could stick with the XPG version, but we need to support
27 * Red Hat 9, which only supports the GNU version.
29 * Furthermore, I do NOT want to export the GNU version in Mono.Posix.dll,
30 * as that's supposed to contain *standard* function definitions (give or
31 * take a few GNU extensions). Portability trumps all.
33 * Consequently, we export the functionality of the XPG version.
34 * Internally, we se the GNU version if _GNU_SOURCE is defined, otherwise
35 * we assume that the XPG version is present.
38 #ifdef _GNU_SOURCE
39 #define mph_min(x,y) ((x) <= (y) ? (x) : (y))
41 /* If you pass an invalid errno value to glibc 2.3.2's strerror_r, you get
42 * back the string "Unknown error" with the error value appended. */
43 static const char mph_unknown[] = "Unknown error ";
46 * Translate the GNU semantics to the XPG semantics.
48 * From reading the (RH9-using) GLibc 2.3.2 sysdeps/generic/_strerror.c,
49 * we can say the following:
50 * - If errnum is a valid error number, a pointer to a constant string is
51 * returned. Thus, the prototype *lies* (it's not really a char*).
52 * `buf' is unchanged (WTF?).
53 * - If errnum is an *invalid* error number, an error message is copied
54 * into `buf' and `buf' is returned. The error message returned is
55 * "Unknown error %i", where %i is the input errnum.
57 * Meanwhile, XPG always modifies `buf' if there's enough space, and either
58 * returns 0 (success) or -1 (error) with errno = EINVAL (bad errnum) or
59 * ERANGE (`buf' isn't big enough). Also, GLibc 2.3.3 (which has the XPG
60 * version) first checks the validity of errnum first, then does the copy.
62 * Assuming that the GNU implementation doesn't change much (ha!), we can
63 * check for EINVAL by comparing the strerror_r return to `buf', OR by
64 * comparing the return value to "Uknown error". (This assumes that
65 * strerror_r will always only return the input buffer for errors.)
67 * Check for ERANGE by comparing the string length returned by strerror_r to
68 * `n'.
70 * Then pray that this actually works...
72 gint32
73 Mono_Posix_Syscall_strerror_r (int errnum, char *buf, mph_size_t n)
75 char *r;
76 char ebuf [sizeof(mph_unknown)];
77 size_t len;
78 size_t blen;
80 mph_return_if_size_t_overflow (n);
82 /* first, check for valid errnum */
83 r = strerror_r (errnum, ebuf, sizeof(ebuf));
84 len = strlen (r);
86 if (r == ebuf ||
87 strncmp (r, mph_unknown, mph_min (len, sizeof(mph_unknown))) == 0) {
88 errno = EINVAL;
89 return -1;
92 /* valid errnum (we hope); is buffer big enough? */
93 blen = (size_t) n;
94 if ((len+1) > blen) {
95 errno = ERANGE;
96 return -1;
99 strncpy (buf, r, len);
100 buf[len] = '\0';
102 return 0;
105 #else /* !def _GNU_SOURCE */
107 gint32
108 Mono_Posix_Syscall_strerror_r (int errnum, char *buf, mph_size_t n)
110 mph_return_if_size_t_overflow (n);
111 return strerror_r (errnum, buf, (size_t) n);
114 #endif /* def _GNU_SOURCE */
116 #endif /* def HAVE_STRERROR_R */
118 G_END_DECLS
121 * vim: noexpandtab