support/errno.c

   1 /*
   2  * <errno.h> wrapper functions.
   3  */
   4
   5 #include <errno.h>
   6 #include <string.h>
   7 #include "mph.h"
   8 #include <stdio.h>
   9
  10 G_BEGIN_DECLS
  11
  12 void
  13 Mono_Posix_Stdlib_SetLastError (int error_number)
  14 {
  15         errno = error_number;
  16 }
  17
  18 #ifdef HAVE_STRERROR_R
  19
  20 /*
  21  * There are two versions of strerror_r:
  22  *  - the GNU version:  char *strerror_r (int errnum, char *buf, size_t n);
  23  *  - the XPG version:    int strerror_r (int errnum, char *buf, size_t n);
  24  *
  25  * Ideally I could stick with the XPG version, but we need to support
  26  * Red Hat 9, which only supports the GNU version.
  27  *
  28  * Furthermore, I do NOT want to export the GNU version in Mono.Posix.dll,
  29  * as that's supposed to contain *standard* function definitions (give or
  30  * take a few GNU extensions).  Portability trumps all.
  31  *
  32  * Consequently, we export the functionality of the XPG version.
  33  * Internally, we se the GNU version if _GNU_SOURCE is defined, otherwise
  34  * we assume that the XPG version is present.
  35  */
  36
  37 #ifdef _GNU_SOURCE
  38 #define mph_min(x,y) ((x) <= (y) ? (x) : (y))
  39
  40 /* If you pass an invalid errno value to glibc 2.3.2's strerror_r, you get
  41  * back the string "Unknown error" with the error value appended. */
  42 static const char mph_unknown[] = "Unknown error ";
  43
  44 /*
  45  * Translate the GNU semantics to the XPG semantics.
  46  *
  47  * From reading the (RH9-using) GLibc 2.3.2 sysdeps/generic/_strerror.c,
  48  * we can say the following:
  49  *   - If errnum is a valid error number, a pointer to a constant string is
  50  *     returned.  Thus, the prototype *lies* (it's not really a char*).
  51  *     `buf' is unchanged (WTF?).
  52  *   - If errnum is an *invalid* error number, an error message is copied
  53  *     into `buf' and `buf' is returned.  The error message returned is
  54  *     "Unknown error %i", where %i is the input errnum.
  55  *
  56  * Meanwhile, XPG always modifies `buf' if there's enough space, and either
  57  * returns 0 (success) or -1 (error) with errno = EINVAL (bad errnum) or
  58  * ERANGE (`buf' isn't big enough).  Also, GLibc 2.3.3 (which has the XPG
  59  * version) first checks the validity of errnum first, then does the copy.
  60  *
  61  * Assuming that the GNU implementation doesn't change much (ha!), we can
  62  * check for EINVAL by comparing the strerror_r return to `buf', OR by
  63  * comparing the return value to "Uknown error".  (This assumes that
  64  * strerror_r will always only return the input buffer for errors.)
  65  *
  66  * Check for ERANGE by comparing the string length returned by strerror_r to
  67  * `n'.
  68  *
  69  * Then pray that this actually works...
  70  */
  71 gint32
  72 Mono_Posix_Syscall_strerror_r (int errnum, char *buf, mph_size_t n)
  73 {
  74         char *r;
  75         char ebuf [sizeof(mph_unknown)];
  76         size_t len;
  77         size_t blen;
  78
  79         mph_return_if_size_t_overflow (n);
  80
  81         /* first, check for valid errnum */
  82         r = strerror_r (errnum, ebuf, sizeof(ebuf));
  83         len = strlen (r);
  84
  85         if (r == ebuf ||
  86                         strncmp (r, mph_unknown, mph_min (len, sizeof(mph_unknown))) == 0) {
  87                 errno = EINVAL;
  88                 return -1;
  89         }
  90
  91         /* valid errnum (we hope); is buffer big enough? */
  92         blen = (size_t) n;
  93         if ((len+1) > blen) {
  94                 errno = ERANGE;
  95                 return -1;
  96         }
  97
  98         strncpy (buf, r, len);
  99         buf[len] = '\0';
 100
 101         return 0;
 102 }
 103
 104 #else /* !def _GNU_SOURCE */
 105
 106 gint32
 107 Mono_Posix_Syscall_strerror_r (int errnum, char *buf, mph_size_t n)
 108 {
 109         mph_return_if_size_t_overflow (n);
 110         return strerror_r (errnum, buf, (size_t) n);
 111 }
 112
 113 #endif /* def _GNU_SOURCE */
 114
 115 #endif /* def HAVE_STRERROR_R */
 116
 117 G_END_DECLS
 118
 119 /*
 120  * vim: noexpandtab
 121  */