From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ian Jackson Subject: Re: [PATCH v2] introduce a cache options for PV disks Date: Thu, 27 Jun 2013 19:01:20 +0100 Message-ID: <20940.32240.104096.270080@mariner.uk.xensource.com> References: <20940.26172.875919.504123@mariner.uk.xensource.com> <20940.31210.191976.244639@mariner.uk.xensource.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Stefano Stabellini Cc: xen-devel@lists.xensource.com, Ian Campbell List-Id: xen-devel@lists.xenproject.org Here's the result. I took Anthony Ligouri's ack off it. Ian. commit 21538601f7d4f2de4d518b92ec9212c99be829e8 Author: Stefano Stabellini Date: Thu Jun 27 14:20:51 2013 +0000 xen_disk: support "direct-io-safe" backend option Support backend option "direct-io-safe". This is documented as follows in the Xen backend specification: * direct-io-safe * Values: 0/1 (boolean) * Default Value: 0 * * The underlying storage is not affected by the direct IO memory * lifetime bug. See: * http://lists.xen.org/archives/html/xen-devel/2012-12/msg01154.html * * Therefore this option gives the backend permission to use * O_DIRECT, notwithstanding that bug. * * That is, if this option is enabled, use of O_DIRECT is safe, * in circumstances where we would normally have avoided it as a * workaround for that bug. This option is not relevant for all * backends, and even not necessarily supported for those for * which it is relevant. A backend which knows that it is not * affected by the bug can ignore this option. * * This option doesn't require a backend to use O_DIRECT, so it * should not be used to try to control the caching behaviour. Also, BDRV_O_NATIVE_AIO is ignored if BDRV_O_NOCACHE, so clarify the default flags passed to the qemu block layer. Signed-off-by: Stefano Stabellini diff --git a/hw/block/xen_disk.c b/hw/block/xen_disk.c index 247f32f..091284b 100644 --- a/hw/block/xen_disk.c +++ b/hw/block/xen_disk.c @@ -93,6 +93,7 @@ struct XenBlkDev { char *type; char *dev; char *devtype; + bool directiosafe; const char *fileproto; const char *filename; int ring_ref; @@ -701,6 +702,7 @@ static int blk_init(struct XenDevice *xendev) { struct XenBlkDev *blkdev = container_of(xendev, struct XenBlkDev, xendev); int info = 0; + char *directiosafe = NULL; /* read xenstore entries */ if (blkdev->params == NULL) { @@ -733,6 +735,8 @@ static int blk_init(struct XenDevice *xendev) if (blkdev->devtype == NULL) { blkdev->devtype = xenstore_read_be_str(&blkdev->xendev, "device-type"); } + directiosafe = xenstore_read_be_str(&blkdev->xendev, "direct-io-safe"); + blkdev->directiosafe = (directiosafe && atoi(directiofsafe)); /* do we have all we need? */ if (blkdev->params == NULL || @@ -760,6 +764,8 @@ static int blk_init(struct XenDevice *xendev) xenstore_write_be_int(&blkdev->xendev, "feature-flush-cache", 1); xenstore_write_be_int(&blkdev->xendev, "feature-persistent", 1); xenstore_write_be_int(&blkdev->xendev, "info", info); + + g_free(directiosafe); return 0; out_error: @@ -773,6 +779,8 @@ out_error: blkdev->dev = NULL; g_free(blkdev->devtype); blkdev->devtype = NULL; + g_free(directiosafe); + blkdev->directiosafe = false; return -1; } @@ -783,7 +791,11 @@ static int blk_connect(struct XenDevice *xendev) bool readonly = true; /* read-only ? */ - qflags = BDRV_O_CACHE_WB | BDRV_O_NATIVE_AIO; + if (blkdev->directiosafe) { + qflags = BDRV_O_NOCACHE | BDRV_O_NATIVE_AIO; + } else { + qflags = BDRV_O_CACHE_WB; + } if (strcmp(blkdev->mode, "w") == 0) { qflags |= BDRV_O_RDWR; readonly = false;