28.11.2019 17:23, Markus Armbruster wrote: > Vladimir Sementsov-Ogievskiy <vsement...@virtuozzo.com> writes: > >> Error **errp is almost always OUT-argument: it's assumed to be NULL, or >> pointer to NULL-initialized pointer, or pointer to error_abort or >> error_fatal, for callee to report error. >> >> But very few functions instead get Error **errp as IN-argument: >> it's assumed to be set (or, maybe, NULL), and callee should clean it, >> or add some information. >> >> In such cases, rename errp to errp_in. > > Missing: why is the rename useful?
The main reason is to prepare for coccinelle part. > > It's useful if it helps readers recognize unusual Error ** parameters, > and recognizing unusual Error ** parameters is actually a problem. I'm > not sure it is, but my familiarity with the Error interface may blind > me. > > How many functions have unusual Error **parameters? How are they used? > Any calls that could easily be mistaken as the usual case? See [*] > below. > > You effectively propose a naming convention. error.h should spell it > out. Let me try: > > Any Error ** parameter meant for passing an error to the caller must > be named @errp. No other Error ** parameter may be named @errp. Good > > Observe: > > * I refrain from stipulating how other Error ** parameters are to be > named. You use @errp_in, because the ones you rename are actually > "IN-arguments". However, different uses are conceivable, where > @errp_in would be misleading. > > * If I understand your ERRP_AUTO_PROPAGATE() idea correctly, many > functions that take an Error ** to pass an error to the caller will > also use ERRP_AUTO_PROPAGATE, but not all. Thus, presence of > ERRP_AUTO_PROPAGATE() won't be a reliable indicator of "the Error ** > parameter is for passing an error to the caller". > > * I can't see machinery to help us catch violations of the convention. > >> This patch updates only error API functions. There still a few >> functions with errp-in semantics, they will be updated in further >> commits. > > Splitting the series into individual patches was a bad idea :) > > First, it really needs review as a whole. I'll do that, but now I have > to hunt down the parts. Found so far: > > [PATCH v6] error: rename errp to errp_in where it is IN-argument > [PATCH v6] hmp: drop Error pointer indirection in hmp_handle_error > [PATCH v6] vnc: drop Error pointer indirection in vnc_client_io_error > [PATCH v6] qdev-monitor: well form error hint helpers > [PATCH v6] nbd: well form nbd_iter_channel_error errp handler > [PATCH v6] ppc: well form kvmppc_hint_smt_possible error hint helper > [PATCH v6] 9pfs: well form error hint helpers > [PATCH v6] hw/core/qdev: cleanup Error ** variables > [PATCH v6] block/snapshot: rename Error ** parameter to more common errp > [PATCH v6] hw/i386/amd_iommu: rename Error ** parameter to more common > errp > [PATCH v6] qga: rename Error ** parameter to more common errp > [PATCH v6] monitor/qmp-cmds: rename Error ** parameter to more common > errp > [PATCH v6] hw/s390x: rename Error ** parameter to more common errp > [PATCH v6] hw/sd: drop extra whitespace in sdhci_sysbus_realize() header > [PATCH v6] hw/tpm: rename Error ** parameter to more common errp > [PATCH v6] hw/usb: rename Error ** parameter to more common errp > [PATCH v6] include/qom/object.h: rename Error ** parameter to more > common errp > [PATCH v6] backends/cryptodev: drop local_err from > cryptodev_backend_complete() > [PATCH v6] hw/vfio/ap: drop local_err from vfio_ap_realize .. 19 patches.. should be 21. It's really simple for me to resend them all in one v7 series. Should I? > > [*] The information I asked for above is buried in these patches. I'll > try to dig it up as I go reviewing them. > > Second, it risks some of these "further patches" overtake this one, and > then its commit message will be misleading. Moreover, the other commits > will lack context. > >> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsement...@virtuozzo.com> >> Reviewed-by: Eric Blake <ebl...@redhat.com> >> --- >> >> v6: fix s/errp/errp_in/ in comments corresponding to changed functions >> [Eric] >> add Eric's r-b >> >> include/qapi/error.h | 16 ++++++++-------- >> util/error.c | 30 +++++++++++++++--------------- >> 2 files changed, 23 insertions(+), 23 deletions(-) >> >> diff --git a/include/qapi/error.h b/include/qapi/error.h >> index 3f95141a01..df518644fc 100644 >> --- a/include/qapi/error.h >> +++ b/include/qapi/error.h >> @@ -230,16 +230,16 @@ void error_propagate_prepend(Error **dst_errp, Error >> *local_err, >> const char *fmt, ...); >> >> /* >> - * Prepend some text to @errp's human-readable error message. >> + * Prepend some text to @errp_in'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); >> +void error_vprepend(Error **errp_in, const char *fmt, va_list ap); >> >> /* >> - * Prepend some text to @errp's human-readable error message. >> + * Prepend some text to @errp_in's human-readable error message. >> * The text is made by formatting @fmt, ... like printf(). >> */ >> -void error_prepend(Error **errp, const char *fmt, ...) >> +void error_prepend(Error **errp_in, const char *fmt, ...) >> GCC_FMT_ATTR(2, 3); >> >> /* >> @@ -250,13 +250,13 @@ void error_prepend(Error **errp, const char *fmt, ...) >> * 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. >> + * @errp_in may be NULL, but not &error_fatal or &error_abort. > > That's because the function modifies the error object. > > Hmm, so do error_prepend() and error_vprepend(). I figure we better > update their contract accordingly, and copy the "not &error_fatal or > &error_abort" assertion. Not in this patch. Maybe not even in this > series. > >> * 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, ...) >> +void error_append_hint(Error **errp_in, const char *fmt, ...) >> GCC_FMT_ATTR(2, 3); >> >> /* >> @@ -281,9 +281,9 @@ Error *error_copy(const Error *err); >> void error_free(Error *err); >> >> /* >> - * Convenience function to assert that *@errp is set, then silently free it. >> + * Convenience function to assert that *@errp_in is set, then silently free >> it. > Long line. Suggest: > > * Assert that *@errp_in is set, then silently free it. > * This is a convenience function for use in tests. > >> */ >> -void error_free_or_abort(Error **errp); >> +void error_free_or_abort(Error **errp_in); >> >> /* >> * Convenience function to warn_report() and free @err. >> diff --git a/util/error.c b/util/error.c >> index d4532ce318..275586faa8 100644 >> --- a/util/error.c >> +++ b/util/error.c >> @@ -121,41 +121,41 @@ void error_setg_file_open_internal(Error **errp, >> "Could not open '%s'", filename); >> } >> >> -void error_vprepend(Error **errp, const char *fmt, va_list ap) >> +void error_vprepend(Error **errp_in, const char *fmt, va_list ap) >> { >> GString *newmsg; >> >> - if (!errp) { >> + if (!errp_in) { >> return; >> >> newmsg = g_string_new(NULL); >> g_string_vprintf(newmsg, fmt, ap); >> - g_string_append(newmsg, (*errp)->msg); >> - g_free((*errp)->msg); >> - (*errp)->msg = g_string_free(newmsg, 0); >> + g_string_append(newmsg, (*errp_in)->msg); >> + g_free((*errp_in)->msg); >> + (*errp_in)->msg = g_string_free(newmsg, 0); >> } >> >> -void error_prepend(Error **errp, const char *fmt, ...) >> +void error_prepend(Error **errp_in, const char *fmt, ...) >> { >> va_list ap; >> >> va_start(ap, fmt); >> - error_vprepend(errp, fmt, ap); >> + error_vprepend(errp_in, fmt, ap); >> va_end(ap); >> } >> >> -void error_append_hint(Error **errp, const char *fmt, ...) >> +void error_append_hint(Error **errp_in, const char *fmt, ...) >> { >> va_list ap; >> int saved_errno = errno; >> Error *err; >> >> - if (!errp) { >> + if (!errp_in) { >> return; >> } >> - err = *errp; >> - assert(err && errp != &error_abort && errp != &error_fatal); >> + err = *errp_in; >> + assert(err && errp_in != &error_abort && errp_in != &error_fatal); >> >> if (!err->hint) { >> err->hint = g_string_new(NULL); >> @@ -271,11 +271,11 @@ void error_free(Error *err) >> } >> } >> >> -void error_free_or_abort(Error **errp) >> +void error_free_or_abort(Error **errp_in) >> { >> - assert(errp && *errp); >> - error_free(*errp); >> - *errp = NULL; >> + assert(errp_in && *errp_in); >> + error_free(*errp_in); >> + *errp_in = NULL; >> } >> >> void error_propagate(Error **dst_errp, Error *local_err) > -- Best regards, Vladimir