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  * Opaque error object.
 122  */
 123 typedef struct Error Error;
 124
 125 /*
 126  * Overall category of an error.
 127  * Based on the qapi type QapiErrorClass, but reproduced here for nicer
 128  * enum names.
 129  */
 130 typedef enum ErrorClass {
 131     ERROR_CLASS_GENERIC_ERROR = QAPI_ERROR_CLASS_GENERICERROR,
 132     ERROR_CLASS_COMMAND_NOT_FOUND = QAPI_ERROR_CLASS_COMMANDNOTFOUND,
 133     ERROR_CLASS_DEVICE_ENCRYPTED = QAPI_ERROR_CLASS_DEVICEENCRYPTED,
 134     ERROR_CLASS_DEVICE_NOT_ACTIVE = QAPI_ERROR_CLASS_DEVICENOTACTIVE,
 135     ERROR_CLASS_DEVICE_NOT_FOUND = QAPI_ERROR_CLASS_DEVICENOTFOUND,
 136     ERROR_CLASS_KVM_MISSING_CAP = QAPI_ERROR_CLASS_KVMMISSINGCAP,
 137 } ErrorClass;
 138
 139 /*
 140  * Get @err's human-readable error message.
 141  */
 142 const char *error_get_pretty(Error *err);
 143
 144 /*
 145  * Get @err's error class.
 146  * Note: use of error classes other than ERROR_CLASS_GENERIC_ERROR is
 147  * strongly discouraged.
 148  */
 149 ErrorClass error_get_class(const Error *err);
 150
 151 /*
 152  * Create a new error object and assign it to *@errp.
 153  * If @errp is NULL, the error is ignored.  Don't bother creating one
 154  * then.
 155  * If @errp is &error_abort, print a suitable message and abort().
 156  * If @errp is &error_fatal, print a suitable message and exit(1).
 157  * If @errp is anything else, *@errp must be NULL.
 158  * The new error's class is ERROR_CLASS_GENERIC_ERROR, and its
 159  * human-readable error message is made from printf-style @fmt, ...
 160  * The resulting message should be a single phrase, with no newline or
 161  * trailing punctuation.
 162  * Please don't error_setg(&error_fatal, ...), use error_report() and
 163  * exit(), because that's more obvious.
 164  * Likewise, don't error_setg(&error_abort, ...), use assert().
 165  */
 166 #define error_setg(errp, fmt, ...)                              \
 167     error_setg_internal((errp), __FILE__, __LINE__, __func__,   \
 168                         (fmt), ## __VA_ARGS__)
 169 void error_setg_internal(Error **errp,
 170                          const char *src, int line, const char *func,
 171                          const char *fmt, ...)
 172     GCC_FMT_ATTR(5, 6);
 173
 174 /*
 175  * Just like error_setg(), with @os_error info added to the message.
 176  * If @os_error is non-zero, ": " + strerror(os_error) is appended to
 177  * the human-readable error message.
 178  */
 179 #define error_setg_errno(errp, os_error, fmt, ...)                      \
 180     error_setg_errno_internal((errp), __FILE__, __LINE__, __func__,     \
 181                               (os_error), (fmt), ## __VA_ARGS__)
 182 void error_setg_errno_internal(Error **errp,
 183                                const char *fname, int line, const char *func,
 184                                int os_error, const char *fmt, ...)
 185     GCC_FMT_ATTR(6, 7);
 186
 187 #ifdef _WIN32
 188 /*
 189  * Just like error_setg(), with @win32_error info added to the message.
 190  * If @win32_error is non-zero, ": " + g_win32_error_message(win32_err)
 191  * is appended to the human-readable error message.
 192  */
 193 #define error_setg_win32(errp, win32_err, fmt, ...)                     \
 194     error_setg_win32_internal((errp), __FILE__, __LINE__, __func__,     \
 195                               (win32_err), (fmt), ## __VA_ARGS__)
 196 void error_setg_win32_internal(Error **errp,
 197                                const char *src, int line, const char *func,
 198                                int win32_err, const char *fmt, ...)
 199     GCC_FMT_ATTR(6, 7);
 200 #endif
 201
 202 /*
 203  * Propagate error object (if any) from @local_err to @dst_errp.
 204  * If @local_err is NULL, do nothing (because there's nothing to
 205  * propagate).
 206  * Else, if @dst_errp is NULL, errors are being ignored.  Free the
 207  * error object.
 208  * Else, if @dst_errp is &error_abort, print a suitable message and
 209  * abort().
 210  * Else, if @dst_errp is &error_fatal, print a suitable message and
 211  * exit(1).
 212  * Else, if @dst_errp already contains an error, ignore this one: free
 213  * the error object.
 214  * Else, move the error object from @local_err to *@dst_errp.
 215  * On return, @local_err is invalid.
 216  * Please don't error_propagate(&error_fatal, ...), use
 217  * error_report_err() and exit(), because that's more obvious.
 218  */
 219 void error_propagate(Error **dst_errp, Error *local_err);
 220
 221 /*
 222  * Prepend some text to @errp's human-readable error message.
 223  * The text is made by formatting @fmt, @ap like vprintf().
 224  */
 225 void error_vprepend(Error **errp, const char *fmt, va_list ap);
 226
 227 /*
 228  * Prepend some text to @errp's human-readable error message.
 229  * The text is made by formatting @fmt, ... like printf().
 230  */
 231 void error_prepend(Error **errp, const char *fmt, ...)
 232     GCC_FMT_ATTR(2, 3);
 233
 234 /*
 235  * Append a printf-style human-readable explanation to an existing error.
 236  * @errp may be NULL, but not &error_fatal or &error_abort.
 237  * Trivially the case if you call it only after error_setg() or
 238  * error_propagate().
 239  * May be called multiple times.  The resulting hint should end with a
 240  * newline.
 241  */
 242 void error_append_hint(Error **errp, const char *fmt, ...)
 243     GCC_FMT_ATTR(2, 3);
 244
 245 /*
 246  * Convenience function to report open() failure.
 247  */
 248 #define error_setg_file_open(errp, os_errno, filename)                  \
 249     error_setg_file_open_internal((errp), __FILE__, __LINE__, __func__, \
 250                                   (os_errno), (filename))
 251 void error_setg_file_open_internal(Error **errp,
 252                                    const char *src, int line, const char *func,
 253                                    int os_errno, const char *filename);
 254
 255 /*
 256  * Return an exact copy of @err.
 257  */
 258 Error *error_copy(const Error *err);
 259
 260 /*
 261  * Free @err.
 262  * @err may be NULL.
 263  */
 264 void error_free(Error *err);
 265
 266 /*
 267  * Convenience function to assert that *@errp is set, then silently free it.
 268  */
 269 void error_free_or_abort(Error **errp);
 270
 271 /*
 272  * Convenience function to error_report() and free @err.
 273  */
 274 void error_report_err(Error *err);
 275
 276 /*
 277  * Convenience function to error_prepend(), error_report() and free @err.
 278  */
 279 void error_reportf_err(Error *err, const char *fmt, ...)
 280     GCC_FMT_ATTR(2, 3);
 281
 282 /*
 283  * Just like error_setg(), except you get to specify the error class.
 284  * Note: use of error classes other than ERROR_CLASS_GENERIC_ERROR is
 285  * strongly discouraged.
 286  */
 287 #define error_set(errp, err_class, fmt, ...)                    \
 288     error_set_internal((errp), __FILE__, __LINE__, __func__,    \
 289                        (err_class), (fmt), ## __VA_ARGS__)
 290 void error_set_internal(Error **errp,
 291                         const char *src, int line, const char *func,
 292                         ErrorClass err_class, const char *fmt, ...)
 293     GCC_FMT_ATTR(6, 7);
 294
 295 /*
 296  * Special error destination to abort on error.
 297  * See error_setg() and error_propagate() for details.
 298  */
 299 extern Error *error_abort;
 300
 301 /*
 302  * Special error destination to exit(1) on error.
 303  * See error_setg() and error_propagate() for details.
 304  */
 305 extern Error *error_fatal;
 306
 307 #endif