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-types.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_ENCRYPTED = QAPI_ERROR_CLASS_DEVICEENCRYPTED,
 129     ERROR_CLASS_DEVICE_NOT_ACTIVE = QAPI_ERROR_CLASS_DEVICENOTACTIVE,
 130     ERROR_CLASS_DEVICE_NOT_FOUND = QAPI_ERROR_CLASS_DEVICENOTFOUND,
 131     ERROR_CLASS_KVM_MISSING_CAP = QAPI_ERROR_CLASS_KVMMISSINGCAP,
 132 } ErrorClass;
 133
 134 /*
 135  * Get @err's human-readable error message.
 136  */
 137 const char *error_get_pretty(const Error *err);
 138
 139 /*
 140  * Get @err's error class.
 141  * Note: use of error classes other than ERROR_CLASS_GENERIC_ERROR is
 142  * strongly discouraged.
 143  */
 144 ErrorClass error_get_class(const Error *err);
 145
 146 /*
 147  * Create a new error object and assign it to *@errp.
 148  * If @errp is NULL, the error is ignored.  Don't bother creating one
 149  * then.
 150  * If @errp is &error_abort, print a suitable message and abort().
 151  * If @errp is &error_fatal, print a suitable message and exit(1).
 152  * If @errp is anything else, *@errp must be NULL.
 153  * The new error's class is ERROR_CLASS_GENERIC_ERROR, and its
 154  * human-readable error message is made from printf-style @fmt, ...
 155  * The resulting message should be a single phrase, with no newline or
 156  * trailing punctuation.
 157  * Please don't error_setg(&error_fatal, ...), use error_report() and
 158  * exit(), because that's more obvious.
 159  * Likewise, don't error_setg(&error_abort, ...), use assert().
 160  */
 161 #define error_setg(errp, fmt, ...)                              \
 162     error_setg_internal((errp), __FILE__, __LINE__, __func__,   \
 163                         (fmt), ## __VA_ARGS__)
 164 void error_setg_internal(Error **errp,
 165                          const char *src, int line, const char *func,
 166                          const char *fmt, ...)
 167     GCC_FMT_ATTR(5, 6);
 168
 169 /*
 170  * Just like error_setg(), with @os_error info added to the message.
 171  * If @os_error is non-zero, ": " + strerror(os_error) is appended to
 172  * the human-readable error message.
 173  *
 174  * The value of errno (which usually can get clobbered by almost any
 175  * function call) will be preserved.
 176  */
 177 #define error_setg_errno(errp, os_error, fmt, ...)                      \
 178     error_setg_errno_internal((errp), __FILE__, __LINE__, __func__,     \
 179                               (os_error), (fmt), ## __VA_ARGS__)
 180 void error_setg_errno_internal(Error **errp,
 181                                const char *fname, int line, const char *func,
 182                                int os_error, const char *fmt, ...)
 183     GCC_FMT_ATTR(6, 7);
 184
 185 #ifdef _WIN32
 186 /*
 187  * Just like error_setg(), with @win32_error info added to the message.
 188  * If @win32_error is non-zero, ": " + g_win32_error_message(win32_err)
 189  * is appended to the human-readable error message.
 190  */
 191 #define error_setg_win32(errp, win32_err, fmt, ...)                     \
 192     error_setg_win32_internal((errp), __FILE__, __LINE__, __func__,     \
 193                               (win32_err), (fmt), ## __VA_ARGS__)
 194 void error_setg_win32_internal(Error **errp,
 195                                const char *src, int line, const char *func,
 196                                int win32_err, const char *fmt, ...)
 197     GCC_FMT_ATTR(6, 7);
 198 #endif
 199
 200 /*
 201  * Propagate error object (if any) from @local_err to @dst_errp.
 202  * If @local_err is NULL, do nothing (because there's nothing to
 203  * propagate).
 204  * Else, if @dst_errp is NULL, errors are being ignored.  Free the
 205  * error object.
 206  * Else, if @dst_errp is &error_abort, print a suitable message and
 207  * abort().
 208  * Else, if @dst_errp is &error_fatal, print a suitable message and
 209  * exit(1).
 210  * Else, if @dst_errp already contains an error, ignore this one: free
 211  * the error object.
 212  * Else, move the error object from @local_err to *@dst_errp.
 213  * On return, @local_err is invalid.
 214  * Please don't error_propagate(&error_fatal, ...), use
 215  * error_report_err() and exit(), because that's more obvious.
 216  */
 217 void error_propagate(Error **dst_errp, Error *local_err);
 218
 219 /*
 220  * Prepend some text to @errp's human-readable error message.
 221  * The text is made by formatting @fmt, @ap like vprintf().
 222  */
 223 void error_vprepend(Error **errp, const char *fmt, va_list ap);
 224
 225 /*
 226  * Prepend some text to @errp's human-readable error message.
 227  * The text is made by formatting @fmt, ... like printf().
 228  */
 229 void error_prepend(Error **errp, const char *fmt, ...)
 230     GCC_FMT_ATTR(2, 3);
 231
 232 /*
 233  * Append a printf-style human-readable explanation to an existing error.
 234  * @errp may be NULL, but not &error_fatal or &error_abort.
 235  * Trivially the case if you call it only after error_setg() or
 236  * error_propagate().
 237  * May be called multiple times.  The resulting hint should end with a
 238  * newline.
 239  */
 240 void error_append_hint(Error **errp, const char *fmt, ...)
 241     GCC_FMT_ATTR(2, 3);
 242
 243 /*
 244  * Convenience function to report open() failure.
 245  */
 246 #define error_setg_file_open(errp, os_errno, filename)                  \
 247     error_setg_file_open_internal((errp), __FILE__, __LINE__, __func__, \
 248                                   (os_errno), (filename))
 249 void error_setg_file_open_internal(Error **errp,
 250                                    const char *src, int line, const char *func,
 251                                    int os_errno, const char *filename);
 252
 253 /*
 254  * Return an exact copy of @err.
 255  */
 256 Error *error_copy(const Error *err);
 257
 258 /*
 259  * Free @err.
 260  * @err may be NULL.
 261  */
 262 void error_free(Error *err);
 263
 264 /*
 265  * Convenience function to assert that *@errp is set, then silently free it.
 266  */
 267 void error_free_or_abort(Error **errp);
 268
 269 /*
 270  * Convenience function to error_report() and free @err.
 271  */
 272 void error_report_err(Error *err);
 273
 274 /*
 275  * Convenience function to error_prepend(), error_report() and free @err.
 276  */
 277 void error_reportf_err(Error *err, const char *fmt, ...)
 278     GCC_FMT_ATTR(2, 3);
 279
 280 /*
 281  * Just like error_setg(), except you get to specify the error class.
 282  * Note: use of error classes other than ERROR_CLASS_GENERIC_ERROR is
 283  * strongly discouraged.
 284  */
 285 #define error_set(errp, err_class, fmt, ...)                    \
 286     error_set_internal((errp), __FILE__, __LINE__, __func__,    \
 287                        (err_class), (fmt), ## __VA_ARGS__)
 288 void error_set_internal(Error **errp,
 289                         const char *src, int line, const char *func,
 290                         ErrorClass err_class, const char *fmt, ...)
 291     GCC_FMT_ATTR(6, 7);
 292
 293 /*
 294  * Special error destination to abort on error.
 295  * See error_setg() and error_propagate() for details.
 296  */
 297 extern Error *error_abort;
 298
 299 /*
 300  * Special error destination to exit(1) on error.
 301  * See error_setg() and error_propagate() for details.
 302  */
 303 extern Error *error_fatal;
 304
 305 #endif