From 8d780f43921feb7fd8d0b58f779a22d1265f2378 Mon Sep 17 00:00:00 2001 From: Markus Armbruster Date: Tue, 17 Nov 2015 17:05:49 +0100 Subject: error: Document how to accumulate multiple errors Suggested-by: Eric Blake Signed-off-by: Markus Armbruster Reviewed-by: Eric Blake Message-Id: <1447776349-2344-1-git-send-email-armbru@redhat.com> --- include/qapi/error.h | 17 +++++++++++++++++ 1 file changed, 17 insertions(+) (limited to 'include/qapi') diff --git a/include/qapi/error.h b/include/qapi/error.h index 6285cf50d1..1480f59ec5 100644 --- a/include/qapi/error.h +++ b/include/qapi/error.h @@ -76,6 +76,23 @@ * But when all you do with the error is pass it on, please use * foo(arg, errp); * for readability. + * + * 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 + * foo(arg, &err); + * bar(arg, &err); // WRONG! + * if (err) { + * handle the error... + * } + * because this may pass a non-null err to bar(). */ #ifndef ERROR_H -- cgit v1.2.3-55-g7522 From f4d0064afcff4c38b379800674938cde8f069dcd Mon Sep 17 00:00:00 2001 From: Markus Armbruster Date: Fri, 18 Dec 2015 16:35:08 +0100 Subject: error: Improve documentation While there, tighten error_append_hint()'s assertion. Signed-off-by: Markus Armbruster Message-Id: <1450452927-8346-6-git-send-email-armbru@redhat.com> Reviewed-by: Eric Blake --- include/qapi/error.h | 20 ++++++++++++++++++-- util/error.c | 2 +- util/qemu-error.c | 8 ++++---- 3 files changed, 23 insertions(+), 7 deletions(-) (limited to 'include/qapi') diff --git a/include/qapi/error.h b/include/qapi/error.h index 1480f59ec5..b18a608c6d 100644 --- a/include/qapi/error.h +++ b/include/qapi/error.h @@ -18,6 +18,15 @@ * Create an error: * error_setg(&err, "situation normal, all fouled up"); * + * Create an error and add additional explanation: + * error_setg(&err, "invalid quark"); + * error_append_hint(&err, "Valid quarks are up, down, strange, " + * "charm, top, bottom.\n"); + * + * Do *not* contract this to + * error_setg(&err, "invalid quark\n" + * "Valid quarks are up, down, strange, charm, top, bottom."); + * * Report an error to stderr: * error_report_err(err); * This frees the error object. @@ -26,6 +35,7 @@ * 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(). * * Handle an error without reporting it (just for completeness): * error_free(err); @@ -142,6 +152,8 @@ ErrorClass error_get_class(const Error *err); * 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. */ #define error_setg(errp, fmt, ...) \ error_setg_internal((errp), __FILE__, __LINE__, __func__, \ @@ -198,7 +210,11 @@ void error_propagate(Error **dst_errp, Error *local_err); /** * Append a printf-style human-readable explanation to an existing error. - * May be called multiple times, and safe if @errp is NULL. + * @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 **errp, const char *fmt, ...) GCC_FMT_ATTR(2, 3); @@ -232,7 +248,7 @@ void error_free_or_abort(Error **errp); /* * Convenience function to error_report() and free @err. */ -void error_report_err(Error *); +void error_report_err(Error *err); /* * Just like error_setg(), except you get to specify the error class. diff --git a/util/error.c b/util/error.c index 9b27c4508e..ebfb74b02e 100644 --- a/util/error.c +++ b/util/error.c @@ -132,7 +132,7 @@ void error_append_hint(Error **errp, const char *fmt, ...) return; } err = *errp; - assert(err && errp != &error_abort); + assert(err && errp != &error_abort && errp != &error_fatal); if (!err->hint) { err->hint = g_string_new(NULL); diff --git a/util/qemu-error.c b/util/qemu-error.c index c1574bb348..ecf5708478 100644 --- a/util/qemu-error.c +++ b/util/qemu-error.c @@ -200,8 +200,8 @@ static void error_print_loc(void) bool enable_timestamp_msg; /* * Print an error message to current monitor if we have one, else to stderr. - * Format arguments like vsprintf(). The result should not contain - * newlines. + * Format arguments like vsprintf(). The resulting message should be + * a single phrase, with no newline or trailing punctuation. * Prepend the current location and append a newline. * It's wrong to call this in a QMP monitor. Use error_setg() there. */ @@ -224,8 +224,8 @@ void error_vreport(const char *fmt, va_list ap) /* * Print an error message to current monitor if we have one, else to stderr. - * Format arguments like sprintf(). The result should not contain - * newlines. + * Format arguments like sprintf(). The resulting message should be a + * single phrase, with no newline or trailing punctuation. * Prepend the current location and append a newline. * It's wrong to call this in a QMP monitor. Use error_setg() there. */ -- cgit v1.2.3-55-g7522 From 8277d2aa58fe4f8f3ee394ea647ea652faf822a4 Mon Sep 17 00:00:00 2001 From: Markus Armbruster Date: Fri, 18 Dec 2015 16:35:12 +0100 Subject: error: New error_prepend(), error_reportf_err() Instead of simply propagating an error verbatim, we sometimes want to add to its message, like this: frobnicate(arg, &err); error_setg(errp, "Can't frobnicate %s: %s", arg, error_get_pretty(err)); error_free(err); This is suboptimal, because it loses err's hint (if any). Moreover, when errp is &error_abort or is subsequently propagated to &error_abort, the abort message points to the place where we last added to the error, not to the place where it originated. To avoid these issues, provide means to add to an error's message in place: frobnicate(arg, errp); error_prepend(errp, "Can't frobnicate %s: ", arg); Likewise, reporting an error like frobnicate(arg, &err); error_report("Can't frobnicate %s: %s", arg, error_get_pretty(err)); can lose err's hint. To avoid: error_reportf_err(err, "Can't frobnicate %s: ", arg); The next commits will put these functions to use. Signed-off-by: Markus Armbruster Reviewed-by: Eric Blake Message-Id: <1450452927-8346-10-git-send-email-armbru@redhat.com> --- include/qapi/error.h | 31 +++++++++++++++++++++++++++++-- util/error.c | 33 +++++++++++++++++++++++++++++++++ 2 files changed, 62 insertions(+), 2 deletions(-) (limited to 'include/qapi') diff --git a/include/qapi/error.h b/include/qapi/error.h index b18a608c6d..45d6c72dee 100644 --- a/include/qapi/error.h +++ b/include/qapi/error.h @@ -31,6 +31,9 @@ * error_report_err(err); * This frees the error object. * + * Report an error to stderr 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... @@ -48,6 +51,10 @@ * error_propagate(errp, err); * where Error **errp is a parameter, by convention the last one. * + * Pass an existing error to the caller with the message modified: + * error_propagate(errp, err); + * error_prepend(errp, "Could not frobnicate '%s': ", name); + * * Create a new error and pass it to the caller: * error_setg(errp, "situation normal, all fouled up"); * @@ -108,9 +115,10 @@ #ifndef ERROR_H #define ERROR_H +#include +#include #include "qemu/compiler.h" #include "qapi-types.h" -#include /* * Opaque error object. @@ -208,7 +216,20 @@ void error_setg_win32_internal(Error **errp, */ void error_propagate(Error **dst_errp, Error *local_err); -/** +/* + * Prepend some text to @errp's human-readable error message. + * The text is made by formatting @fmt, @ap like vprintf(). + */ +void error_vprepend(Error **errp, const char *fmt, va_list ap); + +/* + * Prepend some text to @errp's human-readable error message. + * The text is made by formatting @fmt, ... like printf(). + */ +void error_prepend(Error **errp, const char *fmt, ...) + GCC_FMT_ATTR(2, 3); + +/* * Append a printf-style human-readable explanation to an existing error. * @errp may be NULL, but not &error_fatal or &error_abort. * Trivially the case if you call it only after error_setg() or @@ -250,6 +271,12 @@ void error_free_or_abort(Error **errp); */ void error_report_err(Error *err); +/* + * Convenience function to error_prepend(), error_report() and free @err. + */ +void error_reportf_err(Error *err, const char *fmt, ...) + GCC_FMT_ATTR(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 diff --git a/util/error.c b/util/error.c index ebfb74b02e..57303fd05c 100644 --- a/util/error.c +++ b/util/error.c @@ -122,6 +122,29 @@ void error_setg_file_open_internal(Error **errp, "Could not open '%s'", filename); } +void error_vprepend(Error **errp, const char *fmt, va_list ap) +{ + GString *newmsg; + + if (!errp) { + return; + } + + newmsg = g_string_new(NULL); + g_string_vprintf(newmsg, fmt, ap); + g_string_append(newmsg, (*errp)->msg); + (*errp)->msg = g_string_free(newmsg, 0); +} + +void error_prepend(Error **errp, const char *fmt, ...) +{ + va_list ap; + + va_start(ap, fmt); + error_vprepend(errp, fmt, ap); + va_end(ap); +} + void error_append_hint(Error **errp, const char *fmt, ...) { va_list ap; @@ -209,6 +232,16 @@ void error_report_err(Error *err) error_free(err); } +void error_reportf_err(Error *err, const char *fmt, ...) +{ + va_list ap; + + va_start(ap, fmt); + error_vprepend(&err, fmt, ap); + va_end(ap); + error_report_err(err); +} + void error_free(Error *err) { if (err) { -- cgit v1.2.3-55-g7522