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Thu, 6 Feb 2020 10:53:05 +0000 (UTC) Received: from dresden.str.redhat.com (unknown [10.36.118.15]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 8DF725DA7D; Thu, 6 Feb 2020 10:53:03 +0000 (UTC) Subject: Re: [PATCH v2 04/33] block: Add BdrvChildRole to BdrvChild To: Eric Blake , qemu-block@nongnu.org References: <20200204170848.614480-1-mreitz@redhat.com> <20200204170848.614480-5-mreitz@redhat.com> <3113019f-797f-fe89-abbd-280bbddded31@redhat.com> From: Max Reitz 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: <61ad1ad4-e118-c92c-bbe2-cdd03d02a8d8@redhat.com> Date: Thu, 6 Feb 2020 11:53:02 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.4.1 MIME-Version: 1.0 In-Reply-To: <3113019f-797f-fe89-abbd-280bbddded31@redhat.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="t7lVMFJHsI9fnhDcMjCHzgCnSkRTYJ3x4" X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 205.139.110.120 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: Kevin Wolf , Vladimir Sementsov-Ogievskiy , qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --t7lVMFJHsI9fnhDcMjCHzgCnSkRTYJ3x4 Content-Type: multipart/mixed; boundary="d5MZuXPrCRgOGL9c5ZOiMuNdOELT9P3el" --d5MZuXPrCRgOGL9c5ZOiMuNdOELT9P3el Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable On 05.02.20 16:33, Eric Blake wrote: > On 2/4/20 11:08 AM, Max Reitz wrote: >> For now, it is always set to 0.=C2=A0 Later patches in this series will >> ensure that all callers pass an appropriate combination of flags. >=20 > Sneaky - this re-adds the field you dropped as part of a rename in 2/33. > =C2=A0Anyone doing backport had better be aware that they would need this > whole series, rather than cherry-picking later patches without the > earlier ones.=C2=A0 But that observation does not affect the patch validi= ty. >=20 >> >> Signed-off-by: Max Reitz >> --- >=20 >> +++ b/block.c >> @@ -2381,6 +2381,7 @@ static void bdrv_replace_child(BdrvChild *child, >> BlockDriverState *new_bs) >> =C2=A0 BdrvChild *bdrv_root_attach_child(BlockDriverState *child_bs, >> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0= =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 const char = *child_name, >> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0= =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 const BdrvC= hildClass *child_class, >> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0= =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 BdrvChildRole child_= role, >=20 > Hmm - C is loose enough to allow the declaration of a parameter as an > enum type even when its intended usage is to receive a bitwise-or > derived from that enum but not declared in the enum.=C2=A0 For example, i= f I > understand intent correctly, a caller might pass in 0x3 > (BDRV_CHILD_DATA|BDRV_CHILD_METADATA) which does NOT appear in > BdrvChildRole.=C2=A0 It feels like it might be cleaner to document the > interface as taking an unsigned int (although then you've lost the > documentation that the int is derived from BdrvChildRole), than to abuse > the typesystem to pass values that are not BdrvChildRole through the > parameter. I don=E2=80=99t necessarily disagree, but we have pre-existing examples of = such abuse, like BdrvRequestFlags. The advantage of using BdrvChildRole as a type here is to show that we expect values from that enum. I personally prefer that. I mean, we could do something else entirely and name the enum =E2=80=9CBdrvChildRoleBits=E2=80=9D and add a =E2=80=9Ctypedef unsigned int= BdrvChildRole;=E2=80=9D. I don=E2=80=99t think we=E2=80=99ve ever done that before but maybe it=E2=80= =99d be the cleanest way? Max --d5MZuXPrCRgOGL9c5ZOiMuNdOELT9P3el-- --t7lVMFJHsI9fnhDcMjCHzgCnSkRTYJ3x4 Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEkb62CjDbPohX0Rgp9AfbAGHVz0AFAl478A4ACgkQ9AfbAGHV z0Ab5QgAuLez/ZdVWt8IJQf0ymciu4cYx13JreSKLVxDtPqWngFeionl93UpcHte 6EUPBUNupA9g/4865S8k2rpfpd7KfTMd2qG3+D8k8mKm89DLoZLQAEnKzV2xNRG5 i7S9DRwfkHQITELKmdIeSSfYdv2LijIDmQRC1kdbLAZJlT1eXAqNrFxlBlewSDNq FUuAzUdNgKxzEJzQoDvtGLSepIKJJlQKuqMlnwVxy8YCt1LJ/+YNgwnk+Aze2m7O tWxHND1tIlf/VEi+z8zlnmSB71TJSF+9C+5CHlK3qjaW/ULJpf1Nl5UGQlxA63Gm U448j9pOdo0WzazIN1xJIHpa+gpeeg== =j6qT -----END PGP SIGNATURE----- --t7lVMFJHsI9fnhDcMjCHzgCnSkRTYJ3x4--