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x-sender="postmaster@mail.citrix.com"; x-conformance=sidf_compatible IronPort-SDR: lYPEPaREY4DL5UdRC5M3ckSf4IAECkdpa878CASsb0YtKo3zvfIHnPzbLBK3Tz/Dcfq6CepxMi 1SnFYEKZXLcoNM8+jp48NF/16gGjKaa1MGOlfox0OdIRroJWslu5iZIuXh4qEMhbO/jZkozFNf b2NEJuE101G5wfVQRm5jUZ+GemWqoLIyZpurJLvTrlfJWuLh6FG1iurHzk7VpLXcOa35jO8n8T BKmvg9LLvGfXY8DpCQZPFYNTJPrm0yqnTD7FxbdIEgDo7yTrcM7aYYpXgXhKEeospwf5sca6Y3 UN8= X-SBRS: 2.7 X-MesageID: 4987744 X-Ironport-Server: esa6.hc3370-68.iphmx.com X-Remote-IP: 162.221.158.21 X-Policy: $RELAYED X-IronPort-AV: E=Sophos;i="5.64,437,1559534400"; d="scan'208";a="4987744" From: Anthony PERARD To: Date: Tue, 27 Aug 2019 14:32:59 +0100 Message-ID: <20190827133259.32084-5-anthony.perard@citrix.com> X-Mailer: git-send-email 2.22.0 In-Reply-To: <20190827133259.32084-1-anthony.perard@citrix.com> References: <20190827133259.32084-1-anthony.perard@citrix.com> MIME-Version: 1.0 Subject: [Xen-devel] [PULL 4/4] 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, Peter Maydell 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 Message-Id: <20190823101534.465-3-anthony.perard@citrix.com> --- 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