include/qapi/error.h

   1 /*
   2  * QEMU Error Objects
   3  *
   4  * Copyright IBM, Corp. 2011
   5  * Copyright (C) 2011-2015 Red Hat, Inc.
   6  *
   7  * Authors:
   8  *  Anthony Liguori   <aliguori@us.ibm.com>
   9  *  Markus Armbruster <armbru@redhat.com>
  10  *
  11  * This work is licensed under the terms of the GNU LGPL, version 2.  See
  12  * the COPYING.LIB file in the top-level directory.
  13  */
  14
  15 /*
  16  * Error reporting system loosely patterned after Glib's GError.
  17  *
  18  * Create an error:
  19  *     error_setg(&err, "situation normal, all fouled up");
  20  *
  21  * Create an error and add additional explanation:
  22  *     error_setg(&err, "invalid quark");
  23  *     error_append_hint(&err, "Valid quarks are up, down, strange, "
  24  *                       "charm, top, bottom.\n");
  25  *
  26  * Do *not* contract this to
  27  *     error_setg(&err, "invalid quark\n"
  28  *                "Valid quarks are up, down, strange, charm, top, bottom.");
  29  *
  30  * Report an error to the current monitor if we have one, else stderr:
  31  *     error_report_err(err);
  32  * This frees the error object.
  33  *
  34  * Likewise, but with additional text prepended:
  35  *     error_reportf_err(err, "Could not frobnicate '%s': ", name);
  36  *
  37  * Report an error somewhere else:
  38  *     const char *msg = error_get_pretty(err);
  39  *     do with msg what needs to be done...
  40  *     error_free(err);
  41  * Note that this loses hints added with error_append_hint().
  42  *
  43  * Handle an error without reporting it (just for completeness):
  44  *     error_free(err);
  45  *
  46  * Assert that an expected error occurred, but clean it up without
  47  * reporting it (primarily useful in testsuites):
  48  *     error_free_or_abort(&err);
  49  *
  50  * Pass an existing error to the caller:
  51  *     error_propagate(errp, err);
  52  * where Error **errp is a parameter, by convention the last one.
  53  *
  54  * Pass an existing error to the caller with the message modified:
  55  *     error_propagate(errp, err);
  56  *     error_prepend(errp, "Could not frobnicate '%s': ", name);
  57  *
  58  * Create a new error and pass it to the caller:
  59  *     error_setg(errp, "situation normal, all fouled up");
  60  *
  61  * Call a function and receive an error from it:
  62  *     Error *err = NULL;
  63  *     foo(arg, &err);
  64  *     if (err) {
  65  *         handle the error...
  66  *     }
  67  *
  68  * Call a function ignoring errors:
  69  *     foo(arg, NULL);
  70  *
  71  * Call a function aborting on errors:
  72  *     foo(arg, &error_abort);
  73  *
  74  * Call a function treating errors as fatal:
  75  *     foo(arg, &error_fatal);
  76  *
  77  * Receive an error and pass it on to the caller:
  78  *     Error *err = NULL;
  79  *     foo(arg, &err);
  80  *     if (err) {
  81  *         handle the error...
  82  *         error_propagate(errp, err);
  83  *     }
  84  * where Error **errp is a parameter, by convention the last one.
  85  *
  86  * Do *not* "optimize" this to
  87  *     foo(arg, errp);
  88  *     if (*errp) { // WRONG!
  89  *         handle the error...
  90  *     }
  91  * because errp may be NULL!
  92  *
  93  * But when all you do with the error is pass it on, please use
  94  *     foo(arg, errp);
  95  * for readability.
  96  *
  97  * Receive and accumulate multiple errors (first one wins):
  98  *     Error *err = NULL, *local_err = NULL;
  99  *     foo(arg, &err);
 100  *     bar(arg, &local_err);
 101  *     error_propagate(&err, local_err);
 102  *     if (err) {
 103  *         handle the error...
 104  *     }
 105  *
 106  * Do *not* "optimize" this to
 107  *     foo(arg, &err);
 108  *     bar(arg, &err); // WRONG!
 109  *     if (err) {
 110  *         handle the error...
 111  *     }
 112  * because this may pass a non-null err to bar().
 113  */
 114
 115 #ifndef ERROR_H
 116 #define ERROR_H
 117
 118 #include "qapi/qapi-types-common.h"
 119
 120 /*
 121  * Overall category of an error.
 122  * Based on the qapi type QapiErrorClass, but reproduced here for nicer
 123  * enum names.
 124  */
 125 typedef enum ErrorClass {
 126     ERROR_CLASS_GENERIC_ERROR = QAPI_ERROR_CLASS_GENERICERROR,
 127     ERROR_CLASS_COMMAND_NOT_FOUND = QAPI_ERROR_CLASS_COMMANDNOTFOUND,
 128     ERROR_CLASS_DEVICE_NOT_ACTIVE = QAPI_ERROR_CLASS_DEVICENOTACTIVE,
 129     ERROR_CLASS_DEVICE_NOT_FOUND = QAPI_ERROR_CLASS_DEVICENOTFOUND,
 130     ERROR_CLASS_KVM_MISSING_CAP = QAPI_ERROR_CLASS_KVMMISSINGCAP,
 131 } ErrorClass;
 132
 133 /*
 134  * Get @err's human-readable error message.
 135  */
 136 const char *error_get_pretty(const Error *err);
 137
 138 /*
 139  * Get @err's error class.
 140  * Note: use of error classes other than ERROR_CLASS_GENERIC_ERROR is
 141  * strongly discouraged.
 142  */
 143 ErrorClass error_get_class(const Error *err);
 144
 145 /*
 146  * Create a new error object and assign it to *@errp.
 147  * If @errp is NULL, the error is ignored.  Don't bother creating one
 148  * then.
 149  * If @errp is &error_abort, print a suitable message and abort().
 150  * If @errp is &error_fatal, print a suitable message and exit(1).
 151  * If @errp is anything else, *@errp must be NULL.
 152  * The new error's class is ERROR_CLASS_GENERIC_ERROR, and its
 153  * human-readable error message is made from printf-style @fmt, ...
 154  * The resulting message should be a single phrase, with no newline or
 155  * trailing punctuation.
 156  * Please don't error_setg(&error_fatal, ...), use error_report() and
 157  * exit(), because that's more obvious.
 158  * Likewise, don't error_setg(&error_abort, ...), use assert().
 159  */
 160 #define error_setg(errp, fmt, ...)                              \
 161     error_setg_internal((errp), __FILE__, __LINE__, __func__,   \
 162                         (fmt), ## __VA_ARGS__)
 163 void error_setg_internal(Error **errp,
 164                          const char *src, int line, const char *func,
 165                          const char *fmt, ...)
 166     GCC_FMT_ATTR(5, 6);
 167
 168 /*
 169  * Just like error_setg(), with @os_error info added to the message.
 170  * If @os_error is non-zero, ": " + strerror(os_error) is appended to
 171  * the human-readable error message.
 172  *
 173  * The value of errno (which usually can get clobbered by almost any
 174  * function call) will be preserved.
 175  */
 176 #define error_setg_errno(errp, os_error, fmt, ...)                      \
 177     error_setg_errno_internal((errp), __FILE__, __LINE__, __func__,     \
 178                               (os_error), (fmt), ## __VA_ARGS__)
 179 void error_setg_errno_internal(Error **errp,
 180                                const char *fname, int line, const char *func,
 181                                int os_error, const char *fmt, ...)
 182     GCC_FMT_ATTR(6, 7);
 183
 184 #ifdef _WIN32
 185 /*
 186  * Just like error_setg(), with @win32_error info added to the message.
 187  * If @win32_error is non-zero, ": " + g_win32_error_message(win32_err)
 188  * is appended to the human-readable error message.
 189  */
 190 #define error_setg_win32(errp, win32_err, fmt, ...)                     \
 191     error_setg_win32_internal((errp), __FILE__, __LINE__, __func__,     \
 192                               (win32_err), (fmt), ## __VA_ARGS__)
 193 void error_setg_win32_internal(Error **errp,
 194                                const char *src, int line, const char *func,
 195                                int win32_err, const char *fmt, ...)
 196     GCC_FMT_ATTR(6, 7);
 197 #endif
 198
 199 /*
 200  * Propagate error object (if any) from @local_err to @dst_errp.
 201  * If @local_err is NULL, do nothing (because there's nothing to
 202  * propagate).
 203  * Else, if @dst_errp is NULL, errors are being ignored.  Free the
 204  * error object.
 205  * Else, if @dst_errp is &error_abort, print a suitable message and
 206  * abort().
 207  * Else, if @dst_errp is &error_fatal, print a suitable message and
 208  * exit(1).
 209  * Else, if @dst_errp already contains an error, ignore this one: free
 210  * the error object.
 211  * Else, move the error object from @local_err to *@dst_errp.
 212  * On return, @local_err is invalid.
 213  * Please don't error_propagate(&error_fatal, ...), use
 214  * error_report_err() and exit(), because that's more obvious.
 215  */
 216 void error_propagate(Error **dst_errp, Error *local_err);
 217
 218 /*
 219  * Prepend some text to @errp's human-readable error message.
 220  * The text is made by formatting @fmt, @ap like vprintf().
 221  */
 222 void error_vprepend(Error **errp, const char *fmt, va_list ap);
 223
 224 /*
 225  * Prepend some text to @errp's human-readable error message.
 226  * The text is made by formatting @fmt, ... like printf().
 227  */
 228 void error_prepend(Error **errp, const char *fmt, ...)
 229     GCC_FMT_ATTR(2, 3);
 230
 231 /*
 232  * Append a printf-style human-readable explanation to an existing error.
 233  * If the error is later reported to a human user with
 234  * error_report_err() or warn_report_err(), the hints will be shown,
 235  * too.  If it's reported via QMP, the hints will be ignored.
 236  * Intended use is adding helpful hints on the human user interface,
 237  * e.g. a list of valid values.  It's not for clarifying a confusing
 238  * error message.
 239  * @errp may be NULL, but not &error_fatal or &error_abort.
 240  * Trivially the case if you call it only after error_setg() or
 241  * error_propagate().
 242  * May be called multiple times.  The resulting hint should end with a
 243  * newline.
 244  */
 245 void error_append_hint(Error **errp, const char *fmt, ...)
 246     GCC_FMT_ATTR(2, 3);
 247
 248 /*
 249  * Convenience function to report open() failure.
 250  */
 251 #define error_setg_file_open(errp, os_errno, filename)                  \
 252     error_setg_file_open_internal((errp), __FILE__, __LINE__, __func__, \
 253                                   (os_errno), (filename))
 254 void error_setg_file_open_internal(Error **errp,
 255                                    const char *src, int line, const char *func,
 256                                    int os_errno, const char *filename);
 257
 258 /*
 259  * Return an exact copy of @err.
 260  */
 261 Error *error_copy(const Error *err);
 262
 263 /*
 264  * Free @err.
 265  * @err may be NULL.
 266  */
 267 void error_free(Error *err);
 268
 269 /*
 270  * Convenience function to assert that *@errp is set, then silently free it.
 271  */
 272 void error_free_or_abort(Error **errp);
 273
 274 /*
 275  * Convenience function to warn_report() and free @err.
 276  * The report includes hints added with error_append_hint().
 277  */
 278 void warn_report_err(Error *err);
 279
 280 /*
 281  * Convenience function to error_report() and free @err.
 282  * The report includes hints added with error_append_hint().
 283  */
 284 void error_report_err(Error *err);
 285
 286 /*
 287  * Convenience function to error_prepend(), warn_report() and free @err.
 288  */
 289 void warn_reportf_err(Error *err, const char *fmt, ...)
 290     GCC_FMT_ATTR(2, 3);
 291
 292 /*
 293  * Convenience function to error_prepend(), error_report() and free @err.
 294  */
 295 void error_reportf_err(Error *err, const char *fmt, ...)
 296     GCC_FMT_ATTR(2, 3);
 297
 298 /*
 299  * Just like error_setg(), except you get to specify the error class.
 300  * Note: use of error classes other than ERROR_CLASS_GENERIC_ERROR is
 301  * strongly discouraged.
 302  */
 303 #define error_set(errp, err_class, fmt, ...)                    \
 304     error_set_internal((errp), __FILE__, __LINE__, __func__,    \
 305                        (err_class), (fmt), ## __VA_ARGS__)
 306 void error_set_internal(Error **errp,
 307                         const char *src, int line, const char *func,
 308                         ErrorClass err_class, const char *fmt, ...)
 309     GCC_FMT_ATTR(6, 7);
 310
 311 /*
 312  * Special error destination to abort on error.
 313  * See error_setg() and error_propagate() for details.
 314  */
 315 extern Error *error_abort;
 316
 317 /*
 318  * Special error destination to exit(1) on error.
 319  * See error_setg() and error_propagate() for details.
 320  */
 321 extern Error *error_fatal;
 322
 323 #endif