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Thu, 10 Sep 2020 13:36:09 +0000 (UTC) Subject: Re: [PATCH 19/29] block/export: Move strong user reference to block_exports From: Max Reitz To: Kevin Wolf , qemu-block@nongnu.org References: <20200907182011.521007-1-kwolf@redhat.com> <20200907182011.521007-20-kwolf@redhat.com> 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: Date: Thu, 10 Sep 2020 15:36:08 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.11.0 MIME-Version: 1.0 In-Reply-To: X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=mreitz@redhat.com X-Mimecast-Spam-Score: 0.002 X-Mimecast-Originator: redhat.com Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="emB0U0vD93Z8svr9D8b1FlylzrmSquclQ" Received-SPF: pass client-ip=207.211.31.120; envelope-from=mreitz@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/09/10 08:35:50 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -56 X-Spam_score: -5.7 X-Spam_bar: ----- X-Spam_report: (-5.7 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, NICE_REPLY_A=-3.576, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=unavailable autolearn_force=no X-Spam_action: no action 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: 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) --emB0U0vD93Z8svr9D8b1FlylzrmSquclQ Content-Type: multipart/mixed; boundary="eBaZYUWinI93RyhXmMJJ8YHzFuJbDFMLE" --eBaZYUWinI93RyhXmMJJ8YHzFuJbDFMLE Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable On 10.09.20 15:33, Max Reitz wrote: > On 07.09.20 20:20, Kevin Wolf wrote: >> The reference owned by the user/monitor that is created when adding the >> export and dropped when removing it was tied to the 'exports' list in >> nbd/server.c. Every block export will have a user reference, so move it >> to the block export level and tie it to the 'block_exports' list in >> block/export/export.c instead. This is necessary for introducing a QMP >> command for removing exports. >> >> Note that exports are present in block_exports even after the user has >> requested shutdown. This is different from NBD's exports where exports >> are immediately removed on a shutdown request, even if they are still in >> the process of shutting down. In order to avoid that the user still >> interacts with an export that is shutting down (and possibly removes it >> a second time), we need to remember if the user actually still owns it. >> >> Signed-off-by: Kevin Wolf >> --- >> include/block/export.h | 8 ++++++++ >> block/export/export.c | 6 ++++++ >> blockdev-nbd.c | 5 ----- >> nbd/server.c | 2 -- >> 4 files changed, 14 insertions(+), 7 deletions(-) >=20 > Reviewed-by: Max Reitz >=20 >> diff --git a/include/block/export.h b/include/block/export.h >> index cdc6e161ea..4833947e89 100644 >> --- a/include/block/export.h >> +++ b/include/block/export.h >> @@ -60,6 +60,14 @@ struct BlockExport { >> */ >> int refcount; >> =20 >> + /* >> + * True if one of the references in refcount belongs to the user. A= fter the >> + * user has dropped their reference, they may not e.g. remove the s= ame >> + * export a second time (which would decrease the refcount without = having >> + * it incremented first). >=20 > Not sure though whether this (or the request_shutdown documentation) > should mention that request_shutdown drops the user reference. Er, no, it shouldn=E2=80=99t, because it doesn=E2=80=99t. Only blk_exp_request_shutdown() does that. Though since that=E2=80=99s a public function (used by nbd/server.c), maybe it should be documented there. Max --eBaZYUWinI93RyhXmMJJ8YHzFuJbDFMLE-- --emB0U0vD93Z8svr9D8b1FlylzrmSquclQ Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEkb62CjDbPohX0Rgp9AfbAGHVz0AFAl9aK8gACgkQ9AfbAGHV z0ATiwf/Tdbn5DIGtJTbwn6C6bPtwWIeKJHJ8TGwbr4+U8goWAalIRljauUpTJUo BmvMI3CFAEBpMJCr7le3Sr9rToUjRcKIZ3YvPD+lhsC4gkbLpQCE/TVG59I49/kp HtDI7rAX0LVsTEJkw/LuyJqPQVE6qo0opCEqwIq32Jm1mupdCVz0JDGhkrAKXudr scAGNMlW7w7gdAHv+tml7YokhCRhLtdz6PwXesjxBH51o54HMFof45WBSrEu9cOH ptwcx2NQO2shr2QV2eKsdLVRl2ArtCVxZW0mk5ePLBYJ5z33kWJ8Ixr9MXGmTMse 36KlSzEdvLnmZAiTyDPNMKjHpq3Esg== =R3WP -----END PGP SIGNATURE----- --emB0U0vD93Z8svr9D8b1FlylzrmSquclQ--