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Thu, 19 Sep 2019 09:33:29 +0000 (UTC) Received: from dresden.str.redhat.com (ovpn-204-52.brq.redhat.com [10.40.204.52]) by smtp.corp.redhat.com (Postfix) with ESMTPS id D6A716013A; Thu, 19 Sep 2019 09:33:20 +0000 (UTC) To: Vladimir Sementsov-Ogievskiy , "qemu-devel@nongnu.org" References: <20190918130244.24257-1-vsementsov@virtuozzo.com> From: Max Reitz Openpgp: preference=signencrypt Autocrypt: addr=mreitz@redhat.com; prefer-encrypt=mutual; keydata= mQENBFXOJlcBCADEyyhOTsoa/2ujoTRAJj4MKA21dkxxELVj3cuILpLTmtachWj7QW+TVG8U /PsMCFbpwsQR7oEy8eHHZwuGQsNpEtNC2G/L8Yka0BIBzv7dEgrPzIu+W3anZXQW4702+uES U29G8TP/NGfXRRHGlbBIH9KNUnOSUD2vRtpOLXkWsV5CN6vQFYgQfFvmp5ZpPeUe6xNplu8V mcTw8OSEDW/ZnxJc8TekCKZSpdzYoxfzjm7xGmZqB18VFwgJZlIibt1HE0EB4w5GsD7x5ekh awIe3RwoZgZDLQMdOitJ1tUc8aqaxvgA4tz6J6st8D8pS//m1gAoYJWGwwIVj1DjTYLtABEB AAG0HU1heCBSZWl0eiA8bXJlaXR6QHJlZGhhdC5jb20+iQFTBBMBCAA9AhsDBQkSzAMABQsJ CAcCBhUICQoLAgQWAgMBAh4BAheABQJVzie5FRhoa3A6Ly9rZXlzLmdudXBnLm5ldAAKCRD0 B9sAYdXPQDcIB/9uNkbYEex1rHKz3mr12uxYMwLOOFY9fstP5aoVJQ1nWQVB6m2cfKGdcRe1 2/nFaHSNAzT0NnKz2MjhZVmcrpyd2Gp2QyISCfb1FbT82GMtXFj1wiHmPb3CixYmWGQUUh+I AvUqsevLA+WihgBUyaJq/vuDVM1/K9Un+w+Tz5vpeMidlIsTYhcsMhn0L9wlCjoucljvbDy/ 8C9L2DUdgi3XTa0ORKeflUhdL4gucWoAMrKX2nmPjBMKLgU7WLBc8AtV+84b9OWFML6NEyo4 4cP7cM/07VlJK53pqNg5cHtnWwjHcbpGkQvx6RUx6F1My3y52vM24rNUA3+ligVEgPYBuQEN BFXOJlcBCADAmcVUNTWT6yLWQHvxZ0o47KCP8OcLqD+67T0RCe6d0LP8GsWtrJdeDIQk+T+F xO7DolQPS6iQ6Ak2/lJaPX8L0BkEAiMuLCKFU6Bn3lFOkrQeKp3u05wCSV1iKnhg0UPji9V2 W5eNfy8F4ZQHpeGUGy+liGXlxqkeRVhLyevUqfU0WgNqAJpfhHSGpBgihUupmyUg7lfUPeRM DzAN1pIqoFuxnN+BRHdAecpsLcbR8sQddXmDg9BpSKozO/JyBmaS1RlquI8HERQoe6EynJhd 64aICHDfj61rp+/0jTIcevxIIAzW70IadoS/y3DVIkuhncgDBvGbF3aBtjrJVP+5ABEBAAGJ ASUEGAEIAA8FAlXOJlcCGwwFCRLMAwAACgkQ9AfbAGHVz0CbFwf9F/PXxQR9i4N0iipISYjU sxVdjJOM2TMut+ZZcQ6NSMvhZ0ogQxJ+iEQ5OjnIputKvPVd5U7WRh+4lF1lB/NQGrGZQ1ic alkj6ocscQyFwfib+xIe9w8TG1CVGkII7+TbS5pXHRxZH1niaRpoi/hYtgzkuOPp35jJyqT/ /ELbqQTDAWcqtJhzxKLE/ugcOMK520dJDeb6x2xVES+S5LXby0D4juZlvUj+1fwZu+7Io5+B bkhSVPb/QdOVTpnz7zWNyNw+OONo1aBUKkhq2UIByYXgORPFnbfMY7QWHcjpBVw9MgC4tGeF R4bv+1nAMMxKmb5VvQCExr0eFhJUAHAhVg== Message-ID: <9f41abd9-bef6-d7f1-0e52-df14a50cbe38@redhat.com> Date: Thu, 19 Sep 2019 11:33:19 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.6.2 (mx1.redhat.com [10.5.110.65]); Thu, 19 Sep 2019 09:33:30 +0000 (UTC) Content-Transfer-Encoding: quoted-printable X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 209.132.183.28 Subject: Re: [Qemu-devel] [RFC] error: auto propagated local_err X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: "fam@euphon.net" , "peter.maydell@linaro.org" , "mst@redhat.com" , "codyprime@gmail.com" , "mark.cave-ayland@ilande.co.uk" , "mdroth@linux.vnet.ibm.com" , "kraxel@redhat.com" , "qemu-block@nongnu.org" , "quintela@redhat.com" , "david@redhat.com" , "armbru@redhat.com" , "pasic@linux.ibm.com" , "borntraeger@de.ibm.com" , "marcandre.lureau@redhat.com" , "rth@twiddle.net" , "farman@linux.ibm.com" , "groug@kaod.org" , "dgilbert@redhat.com" , "alex.williamson@redhat.com" , "qemu-arm@nongnu.org" , "stefanha@redhat.com" , "jsnow@redhat.com" , "david@gibson.dropbear.id.au" , "kwolf@redhat.com" , "berrange@redhat.com" , "cohuck@redhat.com" , "qemu-s390x@nongnu.org" , "sundeep.lkml@gmail.com" , "qemu-ppc@nongnu.org" , "pbonzini@redhat.com" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 19.09.19 11:14, Vladimir Sementsov-Ogievskiy wrote: > 19.09.2019 11:59, Max Reitz wrote: >> On 18.09.19 15:02, Vladimir Sementsov-Ogievskiy wrote: >>> Hi all! >>> >>> Here is a proposal (three of them, actually) of auto propagation for >>> local_err, to not call error_propagate on every exit point, when we >>> deal with local_err. >>> >>> It also may help make Greg's series[1] about error_append_hint smalle= r. >>> >>> See definitions and examples below. >>> >>> I'm cc-ing to this RFC everyone from series[1] CC list, as if we like >>> it, the idea will touch same code (and may be more). >>> >>> [1]: https://lists.gnu.org/archive/html/qemu-devel/2019-09/msg03449.h= tml >>> >>> Signed-off-by: Vladimir Sementsov-Ogievskiy >>> --- >>> include/qapi/error.h | 102 ++++++++++++++++++++++++++++++++++++++++= +++ >>> block.c | 63 ++++++++++++-------------- >>> block/backup.c | 8 +++- >>> block/gluster.c | 7 +++ >>> 4 files changed, 144 insertions(+), 36 deletions(-) >> >> If the combination of =E2=80=9Cif (local_err) { error_propagate(...); = ... }=E2=80=9D is >> what=E2=80=99s cumbersome, can=E2=80=99t this be done simpler by addin= g an >> error_propagate() variant with a return value? >> >> i.e. >> >> bool has_error_then_propagate(Error **errp, Error *err) >> { >> if (!err) { >> return false; >> } >> error_propagate(errp, err); >> return true; >> } >> >> And then turn all instances of >> >> if (local_err) { >> error_propagate(errp, local_err); >> ... >> } >> >> into >> >> if (has_error_then_propagate(errp, local_err)) { >> ... >> } >> >> ? >> >> Max >> >=20 > No, originally cumbersome is introducing local_err in a lot of new plac= es by > Greg's series. MAKE_ERRP_SAFE macro makes it as simple as one macro cal= l > instead (in each function where we need local_err). Does it need more than one local_err per function? Because if it didn=E2=80=99t, I=E2=80=99d find one =E2=80=9CError *local_= err;=E2=80=9D simpler than one macro incantation. (It has the same LoC, and it makes code readers ask the same question: =E2=80=9CWhy do we need it?=E2=80=9D Which has the same answer for both;= but one is immediately readable code, whereas the other is a macro.) > Also, auto-propagation seems correct thing to do, which fits good into > g_auto concept, so even without any macro it just allows to drop severa= l error_propagate > calls (or may be several goto statements to do one error_propagate call= ) into > one definitions. It's the same story like with g_autofree vs g_free. I don=E2=80=99t see the advantage here. You have to do the if () stateme= nt anyway, so it isn=E2=80=99t like you=E2=80=99re saving any LoC. In addit= ion, I personally don=E2=80=99t find code hidden through __attribute__((cleanup)= ) easier to understand than explicitly written code. It isn=E2=80=99t like I don=E2=80=99t like __attribute__((cleanup)). But= it does count under =E2=80=9Cmagic=E2=80=9D in my book, and thus I=E2=80=99d avoid it i= f it doesn=E2=80=99t bring actual advantages. (It does bring actual advantages for things like auto-freeing memory, auto-closing FDs, or zeroing secret buffers before freeing them. In all those cases, you save LoC, and you prevent accidental leakage. I don=E2=80=99t quite see such advantages here, but = I may well be mistaken.) Now Kevin has given an actual advantage, which is that local_err complicates debugging. I=E2=80=99ve never had that problem myself, but t= hat would indeed be an advantage that may warrant some magic. Max