From: Stefano Stabellini <stefano.stabellini@eu.citrix.com> To: xen-devel@lists.xensource.com Cc: Paolo Bonzini <pbonzini@redhat.com>, Ian Jackson <Ian.Jackson@eu.citrix.com>, qemu-devel@nongnu.org, Anthony Liguori <anthony@codemonkey.ws>, Stefano Stabellini <Stefano.Stabellini@eu.citrix.com> Subject: [Qemu-devel] [PATCH v2] xen_disk: support "direct-io-safe" backend option Date: Thu, 27 Jun 2013 19:16:30 +0100 [thread overview] Message-ID: <alpine.DEB.2.02.1306271911210.4782@kaball.uk.xensource.com> (raw) 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. The original proposal for a "cache" backend option has been dropped because it was believed too wide, especially considering that at the moment the backend doesn't have a way to tell the toolstack that it is capable of supporting it. Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com> Signed-off-by: Ian Jackson <Ian.Jackson@eu.citrix.com> diff --git a/hw/block/xen_disk.c b/hw/block/xen_disk.c index 247f32f..727f433 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(directiosafe)); /* 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;
WARNING: multiple messages have this Message-ID (diff)
From: Stefano Stabellini <stefano.stabellini@eu.citrix.com> To: xen-devel@lists.xensource.com Cc: Paolo Bonzini <pbonzini@redhat.com>, Ian Jackson <Ian.Jackson@eu.citrix.com>, qemu-devel@nongnu.org, Anthony Liguori <anthony@codemonkey.ws>, Stefano Stabellini <Stefano.Stabellini@eu.citrix.com> Subject: [PATCH v2] xen_disk: support "direct-io-safe" backend option Date: Thu, 27 Jun 2013 19:16:30 +0100 [thread overview] Message-ID: <alpine.DEB.2.02.1306271911210.4782@kaball.uk.xensource.com> (raw) 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. The original proposal for a "cache" backend option has been dropped because it was believed too wide, especially considering that at the moment the backend doesn't have a way to tell the toolstack that it is capable of supporting it. Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com> Signed-off-by: Ian Jackson <Ian.Jackson@eu.citrix.com> diff --git a/hw/block/xen_disk.c b/hw/block/xen_disk.c index 247f32f..727f433 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(directiosafe)); /* 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;
next reply other threads:[~2013-06-27 18:16 UTC|newest] Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top 2013-06-27 18:16 Stefano Stabellini [this message] 2013-06-27 18:16 ` [PATCH v2] xen_disk: support "direct-io-safe" backend option Stefano Stabellini 2013-06-28 7:56 ` [Qemu-devel] " Paolo Bonzini 2013-06-28 7:56 ` Paolo Bonzini 2013-06-28 10:54 ` [Qemu-devel] " Ian Jackson 2013-06-28 10:54 ` Ian Jackson 2013-06-28 10:57 ` [Qemu-devel] " Stefano Stabellini 2013-06-28 10:57 ` Stefano Stabellini 2013-06-28 8:48 ` [Qemu-devel] " Alex Bligh 2013-06-28 8:48 ` Alex Bligh 2013-06-28 10:44 ` [Qemu-devel] " Ian Jackson 2013-06-28 10:44 ` Ian Jackson 2013-06-28 16:17 ` [Qemu-devel] " Alex Bligh 2013-06-28 16:17 ` Alex Bligh 2013-06-28 16:26 ` [Qemu-devel] " Paolo Bonzini 2013-06-28 16:26 ` Paolo Bonzini 2013-06-28 10:56 ` [Qemu-devel] " Stefano Stabellini 2013-06-28 10:56 ` Stefano Stabellini 2013-06-28 16:16 ` [Qemu-devel] " Stefano Stabellini 2013-06-28 16:51 ` George Dunlap
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