support/errno.c

   1 /*
   2  * <errno.h> wrapper functions.
   3  */
   4
   5 #include <errno.h>
   6 #include <string.h>
   7 #include "map.h"
   8 #include "mph.h"
   9 #include <stdio.h>
  10
  11 G_BEGIN_DECLS
  12
  13 void
  14 Mono_Posix_Stdlib_SetLastError (int error_number)
  15 {
  16         errno = error_number;
  17 }
  18
  19 #ifdef HAVE_STRERROR_R
  20
  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);
  25  *
  26  * Ideally I could stick with the XPG version, but we need to support
  27  * Red Hat 9, which only supports the GNU version.
  28  *
  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.
  32  *
  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.
  36  */
  37
  38 #ifdef _GNU_SOURCE
  39 #define mph_min(x,y) ((x) <= (y) ? (x) : (y))
  40
  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 ";
  44
  45 /*
  46  * Translate the GNU semantics to the XPG semantics.
  47  *
  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.
  56  *
  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.
  61  *
  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.)
  66  *
  67  * Check for ERANGE by comparing the string length returned by strerror_r to
  68  * `n'.
  69  *
  70  * Then pray that this actually works...
  71  */
  72 gint32
  73 Mono_Posix_Syscall_strerror_r (int errnum, char *buf, mph_size_t n)
  74 {
  75         char *r;
  76         char ebuf [sizeof(mph_unknown)];
  77         size_t len;
  78         size_t blen;
  79
  80         mph_return_if_size_t_overflow (n);
  81
  82         /* first, check for valid errnum */
  83         r = strerror_r (errnum, ebuf, sizeof(ebuf));
  84         len = strlen (r);
  85
  86         if (r == ebuf ||
  87                         strncmp (r, mph_unknown, mph_min (len, sizeof(mph_unknown))) == 0) {
  88                 errno = EINVAL;
  89                 return -1;
  90         }
  91
  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;
  97         }
  98
  99         strncpy (buf, r, len);
 100         buf[len] = '\0';
 101
 102         return 0;
 103 }
 104
 105 #else /* !def _GNU_SOURCE */
 106
 107 gint32
 108 Mono_Posix_Syscall_strerror_r (int errnum, char *buf, mph_size_t n)
 109 {
 110         mph_return_if_size_t_overflow (n);
 111         return strerror_r (errnum, buf, (size_t) n);
 112 }
 113
 114 #endif /* def _GNU_SOURCE */
 115
 116 #endif /* def HAVE_STRERROR_R */
 117
 118 G_END_DECLS
 119
 120 /*
 121  * vim: noexpandtab
 122  */