From: Eric Blake <eblake@redhat.com>
To: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>,
qemu-devel@nongnu.org
Cc: "Kevin Wolf" <kwolf@redhat.com>,
"Stefano Stabellini" <sstabellini@kernel.org>,
"Michael Roth" <mdroth@linux.vnet.ibm.com>,
qemu-block@nongnu.org, "Paul Durrant" <paul@xen.org>,
"Laszlo Ersek" <lersek@redhat.com>,
"Cornelia Huck" <cohuck@redhat.com>, "Greg Kurz" <groug@kaod.org>,
"Max Reitz" <mreitz@redhat.com>,
"Gerd Hoffmann" <kraxel@redhat.com>,
"Stefan Hajnoczi" <stefanha@redhat.com>,
"Anthony Perard" <anthony.perard@citrix.com>,
xen-devel@lists.xenproject.org,
"Philippe Mathieu-Daudé" <philmd@redhat.com>,
"Markus Armbruster" <armbru@redhat.com>,
"Stefan Berger" <stefanb@linux.ibm.com>
Subject: Re: [PATCH v6 02/11] error: auto propagated local_err
Date: Fri, 17 Jan 2020 08:18:35 -0600 [thread overview]
Message-ID: <d15df303-7152-d1e6-47b4-4a4c7d68ccf3@redhat.com> (raw)
In-Reply-To: <20200110194158.14190-3-vsementsov@virtuozzo.com>
On 1/10/20 1:41 PM, Vladimir Sementsov-Ogievskiy wrote:
> Here is introduced ERRP_AUTO_PROPAGATE macro, to be used at start of
> functions with errp OUT parameter.
s/with/with an/
>
> It has three goals:
>
> 1. Fix issue with error_fatal & error_prepend/error_append_hint: user
maybe s/&/and/ so it doesn't look like the C & operator.
> can't see this additional information, because exit() happens in
> error_setg earlier than information is added. [Reported by Greg Kurz]
>
> 2. Fix issue with error_abort & error_propagate: when we wrap
and again
> error_abort by local_err+error_propagate, resulting coredump will
s/,/, the/
> refer to error_propagate and not to the place where error happened.
> (the macro itself doesn't fix the issue, but it allows to [3.] drop all
s/allows/allows us/
s/all/the/
> local_err+error_propagate pattern, which will definitely fix the issue)
> [Reported by Kevin Wolf]
>
> 3. Drop local_err+error_propagate pattern, which is used to workaround
> void functions with errp parameter, when caller wants to know resulting
> status. (Note: actually these functions could be merely updated to
> return int error code).
>
> To achieve these goals, we need to add invocation of the macro at start
> of functions, which needs error_prepend/error_append_hint (1.); add
> invocation of the macro at start of functions which do
> local_err+error_propagate scenario the check errors, drop local errors
> from them and just use *errp instead (2., 3.).
To achieve these goals, later patches will add invocations of this macro
at the start of functions with either use
error_prepend/error_append_hint (solving 1) or which use
local_err+error_propagate to check errors, switching those functions to
use *errp instead (solving 2 and 3).
>
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
> ---
>
> - * Receive an error and pass it on to the caller:
> + * Receive an error and pass it on to the caller (DEPRECATED*):
> * Error *err = NULL;
> * foo(arg, &err);
> * if (err) {
> @@ -98,6 +98,50 @@
> * foo(arg, errp);
> * for readability.
> *
> + * DEPRECATED* This pattern is deprecated now, use ERRP_AUTO_PROPAGATE macro
s/use/use the/
> + * instead (defined below).
> + * It's deprecated because of two things:
> + *
> + * 1. Issue with error_abort & error_propagate: when we wrap error_abort by
s/&/and/
> + * local_err+error_propagate, resulting coredump will refer to error_propagate
s/,/, the/
> + * and not to the place where error happened.
> + *
> + * 2. A lot of extra code of the same pattern
> + *
> +/*
> + * ERRP_AUTO_PROPAGATE
> + *
> + * This macro is created to be the first line of a function which use
> + * Error **errp parameter to report error. It's needed only in cases where we
> + * want to use error_prepend, error_append_hint or dereference *errp. It's
> + * still safe (but useless) in other cases.
It doesn't _have_ to be the first line to compile (we require C99+
compilers, which allow declarations after statements); but rather
because it makes it easier for our Coccinelle conversion script to catch
outliers. But I think this text is okay, without calling out that extra
information (maybe the commit message should mention it, though).
> + *
> + * If errp is NULL or points to error_fatal, it is rewritten to point to a
> + * local Error object, which will be automatically propagated to the original
> + * errp on function exit (see error_propagator_cleanup).
> + *
> + * After invocation of this macro it is always safe to dereference errp
> + * (as it's not NULL anymore) and to add information (by error_prepend or
> + * error_append_hint)
> + * (as, if it was error_fatal, we swapped it with a local_error to be
> + * propagated on cleanup).
double () () looks odd, as does the mid-sentence newline.
> + *
> + * Note: we don't wrap the error_abort case, as we want resulting coredump
> + * to point to the place where the error happened, not to error_propagate.
> + */
> +#define ERRP_AUTO_PROPAGATE() \
> + g_auto(ErrorPropagator) _auto_errp_prop = {.errp = errp}; \
> + errp = ((errp == NULL || *errp == error_fatal) \
> + ? &_auto_errp_prop.local_err : errp)
> +
> /*
> * Special error destination to abort on error.
> * See error_setg() and error_propagate() for details.
>
The macro itself is fine, my comments are solely on the commit message
and comments. Depending on how much cleanup Markus is willing to do
rather than require a respin, you can add:
Reviewed-by: Eric Blake <eblake@redhat.com>
--
Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3226
Virtualization: qemu.org | libvirt.org
next prev parent reply other threads:[~2020-01-17 14:20 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-10 19:41 [PATCH v6 00/11] error: auto propagated local_err part I Vladimir Sementsov-Ogievskiy
2020-01-10 19:41 ` [PATCH v6 01/11] qapi/error: add (Error **errp) cleaning APIs Vladimir Sementsov-Ogievskiy
2020-01-15 7:46 ` Greg Kurz
2020-01-17 13:15 ` Eric Blake
2020-01-10 19:41 ` [PATCH v6 02/11] error: auto propagated local_err Vladimir Sementsov-Ogievskiy
2020-01-13 8:50 ` Paul Durrant
2020-01-13 9:25 ` Vladimir Sementsov-Ogievskiy
2020-01-15 18:33 ` Greg Kurz
2020-01-17 14:18 ` Eric Blake [this message]
2020-01-10 19:41 ` [PATCH v6 03/11] scripts: add coccinelle script to use auto propagated errp Vladimir Sementsov-Ogievskiy
2020-01-17 14:24 ` Eric Blake
2020-01-17 14:50 ` Vladimir Sementsov-Ogievskiy
2020-01-10 19:41 ` [PATCH v6 04/11] hw/sd/ssi-sd: fix error handling in ssi_sd_realize Vladimir Sementsov-Ogievskiy
2020-01-17 14:26 ` Eric Blake
2020-01-10 19:41 ` [PATCH v6 05/11] SD (Secure Card): introduce ERRP_AUTO_PROPAGATE Vladimir Sementsov-Ogievskiy
2020-01-10 19:41 ` [PATCH v6 06/11] pflash: " Vladimir Sementsov-Ogievskiy
2020-01-10 19:41 ` [PATCH v6 07/11] fw_cfg: " Vladimir Sementsov-Ogievskiy
2020-01-10 19:41 ` [PATCH v6 08/11] virtio-9p: " Vladimir Sementsov-Ogievskiy
2020-01-13 10:40 ` Greg Kurz
2020-01-10 19:41 ` [PATCH v6 09/11] TPM: " Vladimir Sementsov-Ogievskiy
2020-01-10 19:41 ` [PATCH v6 10/11] nbd: " Vladimir Sementsov-Ogievskiy
2020-01-10 19:41 ` [PATCH v6 11/11] xen: " Vladimir Sementsov-Ogievskiy
2020-01-13 8:57 ` Paul Durrant
2020-01-13 9:25 ` Vladimir Sementsov-Ogievskiy
2020-01-10 20:22 ` [Xen-devel] [PATCH v6 00/11] error: auto propagated local_err part I no-reply
2020-01-30 12:36 ` Vladimir Sementsov-Ogievskiy
2020-01-30 16:50 ` Markus Armbruster
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