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x-sender="postmaster@mail.citrix.com"; x-conformance=sidf_compatible IronPort-SDR: v8P0wpMEi2lEQzdfPnrao0+KylUCNC2SltQiJLyCRaJB/kQ7xkxNq5rE7G/31lWGW305AnybbM Z5UA8PzCKcInMvhzQvCq6I693L/5BRmr6uUQkfU7J12Io7VrjpuX+pBu4HecD/kQmruj8CoO5n N8xmScIB/SPvU2oBRybd5L2ehHrMrj23Sw4RCq7l0ipbTryt4NPBu+sjDR63KZRpcv5RavYdc2 UYVcwMtjayz7xla6MXFDDVkJzCAbnS8d/NmvVXmLPa3TaTmz72/FkSth1JtgDUY/OEJ1ecxlyu cOI= X-SBRS: 2.7 X-MesageID: 4814135 X-Ironport-Server: esa5.hc3370-68.iphmx.com X-Remote-IP: 162.221.158.21 X-Policy: $RELAYED X-IronPort-AV: E=Sophos;i="5.64,420,1559534400"; d="scan'208";a="4814135" From: Anthony PERARD To: Date: Fri, 23 Aug 2019 11:15:34 +0100 Message-ID: <20190823101534.465-3-anthony.perard@citrix.com> X-Mailer: git-send-email 2.22.0 In-Reply-To: <20190823101534.465-1-anthony.perard@citrix.com> References: <20190823101534.465-1-anthony.perard@citrix.com> MIME-Version: 1.0 Subject: [Xen-devel] [PATCH v2 2/2] xen-bus: Avoid rewriting identical values to xenstore X-BeenThere: xen-devel@lists.xenproject.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Cc: Anthony PERARD , xen-devel@lists.xenproject.org, Stefano Stabellini , Paul Durrant Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Errors-To: xen-devel-bounces@lists.xenproject.org Sender: "Xen-devel" X-ZohoMail-DKIM: fail (Header signature does not verify) When QEMU receives a xenstore watch event suggesting that the "state" of the frontend changed, it records this in its own state but it also re-write the value back into xenstore even so there were no change. This triggers an unnecessary xenstore watch event which QEMU will process again (and maybe the frontend as well). Also QEMU could potentially write an already old value. Signed-off-by: Anthony PERARD Reviewed-by: Paul Durrant --- Notes: v2: - fix coding style - only change frontend_set_state() and use 'publish' instead of 'export= '. hw/xen/xen-bus.c | 11 +++++++---- 1 file changed, 7 insertions(+), 4 deletions(-) diff --git a/hw/xen/xen-bus.c b/hw/xen/xen-bus.c index 62c127b926..a04478ad4f 100644 --- a/hw/xen/xen-bus.c +++ b/hw/xen/xen-bus.c @@ -698,7 +698,8 @@ int xen_device_frontend_scanf(XenDevice *xendev, const = char *key, } =20 static void xen_device_frontend_set_state(XenDevice *xendev, - enum xenbus_state state) + enum xenbus_state state, + bool publish) { const char *type =3D object_get_typename(OBJECT(xendev)); =20 @@ -710,7 +711,9 @@ static void xen_device_frontend_set_state(XenDevice *xe= ndev, xs_strstate(state)); =20 xendev->frontend_state =3D state; - xen_device_frontend_printf(xendev, "state", "%u", state); + if (publish) { + xen_device_frontend_printf(xendev, "state", "%u", state); + } } =20 static void xen_device_frontend_changed(void *opaque) @@ -726,7 +729,7 @@ static void xen_device_frontend_changed(void *opaque) state =3D XenbusStateUnknown; } =20 - xen_device_frontend_set_state(xendev, state); + xen_device_frontend_set_state(xendev, state, false); =20 if (state =3D=3D XenbusStateInitialising && xendev->backend_state =3D=3D XenbusStateClosed && @@ -1169,7 +1172,7 @@ static void xen_device_realize(DeviceState *dev, Erro= r **errp) xen_device_frontend_printf(xendev, "backend-id", "%u", xenbus->backend_id); =20 - xen_device_frontend_set_state(xendev, XenbusStateInitialising); + xen_device_frontend_set_state(xendev, XenbusStateInitialising, true); =20 xendev->exit.notify =3D xen_device_exit; qemu_add_exit_notifier(&xendev->exit); --=20 Anthony PERARD _______________________________________________ Xen-devel mailing list Xen-devel@lists.xenproject.org https://lists.xenproject.org/mailman/listinfo/xen-devel