qemu

error.h (18074B)

---

 /*
  * QEMU Error Objects
  *
  * Copyright IBM, Corp. 2011
  * Copyright (C) 2011-2015 Red Hat, Inc.
  *
  * Authors:
  *  Anthony Liguori   <aliguori@us.ibm.com>
  *  Markus Armbruster <armbru@redhat.com>
  *
  * This work is licensed under the terms of the GNU LGPL, version 2.  See
  * the COPYING.LIB file in the top-level directory.
  */
 
 /*
  * Error reporting system loosely patterned after Glib's GError.
  *
  * = Rules =
  *
  * - Functions that use Error to report errors have an Error **errp
  *   parameter.  It should be the last parameter, except for functions
  *   taking variable arguments.
  *
  * - You may pass NULL to not receive the error, &error_abort to abort
  *   on error, &error_fatal to exit(1) on error, or a pointer to a
  *   variable containing NULL to receive the error.
  *
  * - Separation of concerns: the function is responsible for detecting
  *   errors and failing cleanly; handling the error is its caller's
  *   job.  Since the value of @errp is about handling the error, the
  *   function should not examine it.
  *
  * - The function may pass @errp to functions it calls to pass on
  *   their errors to its caller.  If it dereferences @errp to check
  *   for errors, it must use ERRP_GUARD().
  *
  * - On success, the function should not touch *errp.  On failure, it
  *   should set a new error, e.g. with error_setg(errp, ...), or
  *   propagate an existing one, e.g. with error_propagate(errp, ...).
  *
  * - Whenever practical, also return a value that indicates success /
  *   failure.  This can make the error checking more concise, and can
  *   avoid useless error object creation and destruction.  Note that
  *   we still have many functions returning void.  We recommend
  *   • bool-valued functions return true on success / false on failure,
  *   • pointer-valued functions return non-null / null pointer, and
  *   • integer-valued functions return non-negative / negative.
  *
  * = Creating errors =
  *
  * Create an error:
  *     error_setg(errp, "situation normal, all fouled up");
  * where @errp points to the location to receive the error.
  *
  * Create an error and add additional explanation:
  *     error_setg(errp, "invalid quark");
  *     error_append_hint(errp, "Valid quarks are up, down, strange, "
  *                       "charm, top, bottom.\n");
  * This may require use of ERRP_GUARD(); more on that below.
  *
  * Do *not* contract this to
  *     error_setg(errp, "invalid quark\n" // WRONG!
  *                "Valid quarks are up, down, strange, charm, top, bottom.");
  *
  * = Reporting and destroying errors =
  *
  * Report an error to the current monitor if we have one, else stderr:
  *     error_report_err(err);
  * This frees the error object.
  *
  * Likewise, but with additional text prepended:
  *     error_reportf_err(err, "Could not frobnicate '%s': ", name);
  *
  * Report an error somewhere else:
  *     const char *msg = error_get_pretty(err);
  *     do with msg what needs to be done...
  *     error_free(err);
  * Note that this loses hints added with error_append_hint().
  *
  * Call a function ignoring errors:
  *     foo(arg, NULL);
  * This is more concise than
  *     Error *err = NULL;
  *     foo(arg, &err);
  *     error_free(err); // don't do this
  *
  * Call a function aborting on errors:
  *     foo(arg, &error_abort);
  * This is more concise and fails more nicely than
  *     Error *err = NULL;
  *     foo(arg, &err);
  *     assert(!err); // don't do this
  *
  * Call a function treating errors as fatal:
  *     foo(arg, &error_fatal);
  * This is more concise than
  *     Error *err = NULL;
  *     foo(arg, &err);
  *     if (err) { // don't do this
  *         error_report_err(err);
  *         exit(1);
  *     }
  *
  * Handle an error without reporting it (just for completeness):
  *     error_free(err);
  *
  * Assert that an expected error occurred, but clean it up without
  * reporting it (primarily useful in testsuites):
  *     error_free_or_abort(&err);
  *
  * = Passing errors around =
  *
  * Errors get passed to the caller through the conventional @errp
  * parameter.
  *
  * Create a new error and pass it to the caller:
  *     error_setg(errp, "situation normal, all fouled up");
  *
  * Call a function, receive an error from it, and pass it to the caller
  * - when the function returns a value that indicates failure, say
  *   false:
  *     if (!foo(arg, errp)) {
  *         handle the error...
  *     }
  * - when it does not, say because it is a void function:
  *     ERRP_GUARD();
  *     foo(arg, errp);
  *     if (*errp) {
  *         handle the error...
  *     }
  * More on ERRP_GUARD() below.
  *
  * Code predating ERRP_GUARD() still exists, and looks like this:
  *     Error *err = NULL;
  *     foo(arg, &err);
  *     if (err) {
  *         handle the error...
  *         error_propagate(errp, err); // deprecated
  *     }
  * Avoid in new code.  Do *not* "optimize" it to
  *     foo(arg, errp);
  *     if (*errp) { // WRONG!
  *         handle the error...
  *     }
  * because errp may be NULL without the ERRP_GUARD() guard.
  *
  * But when all you do with the error is pass it on, please use
  *     foo(arg, errp);
  * for readability.
  *
  * Receive an error, and handle it locally
  * - when the function returns a value that indicates failure, say
  *   false:
  *     Error *err = NULL;
  *     if (!foo(arg, &err)) {
  *         handle the error...
  *     }
  * - when it does not, say because it is a void function:
  *     Error *err = NULL;
  *     foo(arg, &err);
  *     if (err) {
  *         handle the error...
  *     }
  *
  * Pass an existing error to the caller:
  *     error_propagate(errp, err);
  * This is rarely needed.  When @err is a local variable, use of
  * ERRP_GUARD() commonly results in more readable code.
  *
  * Pass an existing error to the caller with the message modified:
  *     error_propagate_prepend(errp, err,
  *                             "Could not frobnicate '%s': ", name);
  * This is more concise than
  *     error_propagate(errp, err); // don't do this
  *     error_prepend(errp, "Could not frobnicate '%s': ", name);
  * and works even when @errp is &error_fatal.
  *
  * Receive and accumulate multiple errors (first one wins):
  *     Error *err = NULL, *local_err = NULL;
  *     foo(arg, &err);
  *     bar(arg, &local_err);
  *     error_propagate(&err, local_err);
  *     if (err) {
  *         handle the error...
  *     }
  *
  * Do *not* "optimize" this to
  *     Error *err = NULL;
  *     foo(arg, &err);
  *     bar(arg, &err); // WRONG!
  *     if (err) {
  *         handle the error...
  *     }
  * because this may pass a non-null err to bar().
  *
  * Likewise, do *not*
  *     Error *err = NULL;
  *     if (cond1) {
  *         error_setg(&err, ...);
  *     }
  *     if (cond2) {
  *         error_setg(&err, ...); // WRONG!
  *     }
  * because this may pass a non-null err to error_setg().
  *
  * = Why, when and how to use ERRP_GUARD() =
  *
  * Without ERRP_GUARD(), use of the @errp parameter is restricted:
  * - It must not be dereferenced, because it may be null.
  * - It should not be passed to error_prepend() or
  *   error_append_hint(), because that doesn't work with &error_fatal.
  * ERRP_GUARD() lifts these restrictions.
  *
  * To use ERRP_GUARD(), add it right at the beginning of the function.
  * @errp can then be used without worrying about the argument being
  * NULL or &error_fatal.
  *
  * Using it when it's not needed is safe, but please avoid cluttering
  * the source with useless code.
  *
  * = Converting to ERRP_GUARD() =
  *
  * To convert a function to use ERRP_GUARD():
  *
  * 0. If the Error ** parameter is not named @errp, rename it to
  *    @errp.
  *
  * 1. Add an ERRP_GUARD() invocation, by convention right at the
  *    beginning of the function.  This makes @errp safe to use.
  *
  * 2. Replace &err by errp, and err by *errp.  Delete local variable
  *    @err.
  *
  * 3. Delete error_propagate(errp, *errp), replace
  *    error_propagate_prepend(errp, *errp, ...) by error_prepend(errp, ...)
  *
  * 4. Ensure @errp is valid at return: when you destroy *errp, set
  *    *errp = NULL.
  *
  * Example:
  *
  *     bool fn(..., Error **errp)
  *     {
  *         Error *err = NULL;
  *
  *         foo(arg, &err);
  *         if (err) {
  *             handle the error...
  *             error_propagate(errp, err);
  *             return false;
  *         }
  *         ...
  *     }
  *
  * becomes
  *
  *     bool fn(..., Error **errp)
  *     {
  *         ERRP_GUARD();
  *
  *         foo(arg, errp);
  *         if (*errp) {
  *             handle the error...
  *             return false;
  *         }
  *         ...
  *     }
  *
  * For mass-conversion, use scripts/coccinelle/errp-guard.cocci.
  */
 
 #ifndef ERROR_H
 #define ERROR_H
 
 #include "qapi/qapi-types-error.h"
 
 /*
  * Overall category of an error.
  * Based on the qapi type QapiErrorClass, but reproduced here for nicer
  * enum names.
  */
 typedef enum ErrorClass {
     ERROR_CLASS_GENERIC_ERROR = QAPI_ERROR_CLASS_GENERICERROR,
     ERROR_CLASS_COMMAND_NOT_FOUND = QAPI_ERROR_CLASS_COMMANDNOTFOUND,
     ERROR_CLASS_DEVICE_NOT_ACTIVE = QAPI_ERROR_CLASS_DEVICENOTACTIVE,
     ERROR_CLASS_DEVICE_NOT_FOUND = QAPI_ERROR_CLASS_DEVICENOTFOUND,
     ERROR_CLASS_KVM_MISSING_CAP = QAPI_ERROR_CLASS_KVMMISSINGCAP,
 } ErrorClass;
 
 /*
  * Get @err's human-readable error message.
  */
 const char *error_get_pretty(const Error *err);
 
 /*
  * Get @err's error class.
  * Note: use of error classes other than ERROR_CLASS_GENERIC_ERROR is
  * strongly discouraged.
  */
 ErrorClass error_get_class(const Error *err);
 
 /*
  * Create a new error object and assign it to *@errp.
  * If @errp is NULL, the error is ignored.  Don't bother creating one
  * then.
  * If @errp is &error_abort, print a suitable message and abort().
  * If @errp is &error_fatal, print a suitable message and exit(1).
  * If @errp is anything else, *@errp must be NULL.
  * The new error's class is ERROR_CLASS_GENERIC_ERROR, and its
  * human-readable error message is made from printf-style @fmt, ...
  * The resulting message should be a single phrase, with no newline or
  * trailing punctuation.
  * Please don't error_setg(&error_fatal, ...), use error_report() and
  * exit(), because that's more obvious.
  * Likewise, don't error_setg(&error_abort, ...), use assert().
  */
 #define error_setg(errp, fmt, ...)                              \
     error_setg_internal((errp), __FILE__, __LINE__, __func__,   \
                         (fmt), ## __VA_ARGS__)
 void error_setg_internal(Error **errp,
                          const char *src, int line, const char *func,
                          const char *fmt, ...)
     G_GNUC_PRINTF(5, 6);
 
 /*
  * Just like error_setg(), with @os_error info added to the message.
  * If @os_error is non-zero, ": " + strerror(os_error) is appended to
  * the human-readable error message.
  *
  * The value of errno (which usually can get clobbered by almost any
  * function call) will be preserved.
  */
 #define error_setg_errno(errp, os_error, fmt, ...)                      \
     error_setg_errno_internal((errp), __FILE__, __LINE__, __func__,     \
                               (os_error), (fmt), ## __VA_ARGS__)
 void error_setg_errno_internal(Error **errp,
                                const char *fname, int line, const char *func,
                                int os_error, const char *fmt, ...)
     G_GNUC_PRINTF(6, 7);
 
 #ifdef _WIN32
 /*
  * Just like error_setg(), with @win32_error info added to the message.
  * If @win32_error is non-zero, ": " + g_win32_error_message(win32_err)
  * is appended to the human-readable error message.
  */
 #define error_setg_win32(errp, win32_err, fmt, ...)                     \
     error_setg_win32_internal((errp), __FILE__, __LINE__, __func__,     \
                               (win32_err), (fmt), ## __VA_ARGS__)
 void error_setg_win32_internal(Error **errp,
                                const char *src, int line, const char *func,
                                int win32_err, const char *fmt, ...)
     G_GNUC_PRINTF(6, 7);
 #endif
 
 /*
  * Propagate error object (if any) from @local_err to @dst_errp.
  * If @local_err is NULL, do nothing (because there's nothing to
  * propagate).
  * Else, if @dst_errp is NULL, errors are being ignored.  Free the
  * error object.
  * Else, if @dst_errp is &error_abort, print a suitable message and
  * abort().
  * Else, if @dst_errp is &error_fatal, print a suitable message and
  * exit(1).
  * Else, if @dst_errp already contains an error, ignore this one: free
  * the error object.
  * Else, move the error object from @local_err to *@dst_errp.
  * On return, @local_err is invalid.
  * Please use ERRP_GUARD() instead when possible.
  * Please don't error_propagate(&error_fatal, ...), use
  * error_report_err() and exit(), because that's more obvious.
  */
 void error_propagate(Error **dst_errp, Error *local_err);
 
 
 /*
  * Propagate error object (if any) with some text prepended.
  * Behaves like
  *     error_prepend(&local_err, fmt, ...);
  *     error_propagate(dst_errp, local_err);
  * Please use ERRP_GUARD() and error_prepend() instead when possible.
  */
 void error_propagate_prepend(Error **dst_errp, Error *local_err,
                              const char *fmt, ...)
     G_GNUC_PRINTF(3, 4);
 
 /*
  * Prepend some text to @errp's human-readable error message.
  * The text is made by formatting @fmt, @ap like vprintf().
  */
 void error_vprepend(Error *const *errp, const char *fmt, va_list ap)
     G_GNUC_PRINTF(2, 0);
 
 /*
  * Prepend some text to @errp's human-readable error message.
  * The text is made by formatting @fmt, ... like printf().
  */
 void error_prepend(Error *const *errp, const char *fmt, ...)
     G_GNUC_PRINTF(2, 3);
 
 /*
  * Append a printf-style human-readable explanation to an existing error.
  * If the error is later reported to a human user with
  * error_report_err() or warn_report_err(), the hints will be shown,
  * too.  If it's reported via QMP, the hints will be ignored.
  * Intended use is adding helpful hints on the human user interface,
  * e.g. a list of valid values.  It's not for clarifying a confusing
  * error message.
  * @errp may be NULL, but not &error_fatal or &error_abort.
  * Trivially the case if you call it only after error_setg() or
  * error_propagate().
  * May be called multiple times.  The resulting hint should end with a
  * newline.
  */
 void error_append_hint(Error *const *errp, const char *fmt, ...)
     G_GNUC_PRINTF(2, 3);
 
 /*
  * Convenience function to report open() failure.
  */
 #define error_setg_file_open(errp, os_errno, filename)                  \
     error_setg_file_open_internal((errp), __FILE__, __LINE__, __func__, \
                                   (os_errno), (filename))
 void error_setg_file_open_internal(Error **errp,
                                    const char *src, int line, const char *func,
                                    int os_errno, const char *filename);
 
 /*
  * Return an exact copy of @err.
  */
 Error *error_copy(const Error *err);
 
 /*
  * Free @err.
  * @err may be NULL.
  */
 void error_free(Error *err);
 
 /*
  * Convenience function to assert that *@errp is set, then silently free it.
  */
 void error_free_or_abort(Error **errp);
 
 /*
  * Convenience function to warn_report() and free @err.
  * The report includes hints added with error_append_hint().
  */
 void warn_report_err(Error *err);
 
 /*
  * Convenience function to error_report() and free @err.
  * The report includes hints added with error_append_hint().
  */
 void error_report_err(Error *err);
 
 /*
  * Convenience function to error_prepend(), warn_report() and free @err.
  */
 void warn_reportf_err(Error *err, const char *fmt, ...)
     G_GNUC_PRINTF(2, 3);
 
 /*
  * Convenience function to error_prepend(), error_report() and free @err.
  */
 void error_reportf_err(Error *err, const char *fmt, ...)
     G_GNUC_PRINTF(2, 3);
 
 /*
  * Just like error_setg(), except you get to specify the error class.
  * Note: use of error classes other than ERROR_CLASS_GENERIC_ERROR is
  * strongly discouraged.
  */
 #define error_set(errp, err_class, fmt, ...)                    \
     error_set_internal((errp), __FILE__, __LINE__, __func__,    \
                        (err_class), (fmt), ## __VA_ARGS__)
 void error_set_internal(Error **errp,
                         const char *src, int line, const char *func,
                         ErrorClass err_class, const char *fmt, ...)
     G_GNUC_PRINTF(6, 7);
 
 /*
  * Make @errp parameter easier to use regardless of argument value
  *
  * This macro is for use right at the beginning of a function that
  * takes an Error **errp parameter to pass errors to its caller.  The
  * parameter must be named @errp.
  *
  * It must be used when the function dereferences @errp or passes
  * @errp to error_prepend(), error_vprepend(), or error_append_hint().
  * It is safe to use even when it's not needed, but please avoid
  * cluttering the source with useless code.
  *
  * If @errp is NULL or &error_fatal, rewrite it to point to a local
  * Error variable, which will be automatically propagated to the
  * original @errp on function exit.
  *
  * Note: &error_abort is not rewritten, because that would move the
  * abort from the place where the error is created to the place where
  * it's propagated.
  */
 #define ERRP_GUARD()                                            \
     g_auto(ErrorPropagator) _auto_errp_prop = {.errp = errp};   \
     do {                                                        \
         if (!errp || errp == &error_fatal) {                    \
             errp = &_auto_errp_prop.local_err;                  \
         }                                                       \
     } while (0)
 
 typedef struct ErrorPropagator {
     Error *local_err;
     Error **errp;
 } ErrorPropagator;
 
 static inline void error_propagator_cleanup(ErrorPropagator *prop)
 {
     error_propagate(prop->errp, prop->local_err);
 }
 
 G_DEFINE_AUTO_CLEANUP_CLEAR_FUNC(ErrorPropagator, error_propagator_cleanup);
 
 /*
  * Special error destination to abort on error.
  * See error_setg() and error_propagate() for details.
  */
 extern Error *error_abort;
 
 /*
  * Special error destination to exit(1) on error.
  * See error_setg() and error_propagate() for details.
  */
 extern Error *error_fatal;
 
 #endif