| Message ID | 20230601214823.1701-3-demi@invisiblethingslab.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | xen/blkback: support delete-on-close block devices | expand |
> --- a/drivers/block/xen-blkback/xenbus.c > +++ b/drivers/block/xen-blkback/xenbus.c > @@ -3,6 +3,20 @@ > Copyright (C) 2005 Rusty Russell <rusty@rustcorp.com.au> > Copyright (C) 2005 XenSource Ltd > > +In addition to the Xenstore nodes required by the Xen block device > +specification, this implementation of blkback uses a new Xenstore > +node: "opened". blkback sets "opened" to "0" before the hotplug script > +is called. Once the device node has been opened, blkback sets "opened" > +to "1". This is a really odd comment style, and a really strange place for it. To me it feels like this should just be a file in Documentation as it relates to how to use the driver, and doesn't really explain the code.
On Wed, Jun 07, 2023 at 12:46:16AM -0700, Christoph Hellwig wrote: > > --- a/drivers/block/xen-blkback/xenbus.c > > +++ b/drivers/block/xen-blkback/xenbus.c > > @@ -3,6 +3,20 @@ > > Copyright (C) 2005 Rusty Russell <rusty@rustcorp.com.au> > > Copyright (C) 2005 XenSource Ltd > > > > +In addition to the Xenstore nodes required by the Xen block device > > +specification, this implementation of blkback uses a new Xenstore > > +node: "opened". blkback sets "opened" to "0" before the hotplug script > > +is called. Once the device node has been opened, blkback sets "opened" > > +to "1". > > This is a really odd comment style, and a really strange place for it. > To me it feels like this should just be a file in Documentation as it > relates to how to use the driver, and doesn't really explain the code. Will fix in v3.
diff --git a/drivers/block/xen-blkback/xenbus.c b/drivers/block/xen-blkback/xenbus.c index 9c3eb148fbd802c74e626c3d7bcd69dcb09bd921..519a78aa9073d1faa1dce5c1b36e95ae58da534b 100644 --- a/drivers/block/xen-blkback/xenbus.c +++ b/drivers/block/xen-blkback/xenbus.c @@ -3,6 +3,20 @@ Copyright (C) 2005 Rusty Russell <rusty@rustcorp.com.au> Copyright (C) 2005 XenSource Ltd +In addition to the Xenstore nodes required by the Xen block device +specification, this implementation of blkback uses a new Xenstore +node: "opened". blkback sets "opened" to "0" before the hotplug script +is called. Once the device node has been opened, blkback sets "opened" +to "1". + +"opened" is read exclusively by userspace. It serves two purposes: + +1. It tells userspace that diskseq@major:minor syntax for "physical-device" is + supported. + +2. It tells userspace that it can wait for "opened" to be set to 1 after writing + "physical-device". Once "opened" is 1, blkback has a reference to the + device, so userspace doesn't need to keep one. */ @@ -699,6 +713,14 @@ static int xen_blkbk_probe(struct xenbus_device *dev, if (err) pr_warn("%s write out 'max-ring-page-order' failed\n", __func__); + /* + * This informs userspace that the "opened" node will be set to "1" when + * the device has been opened successfully. + */ + err = xenbus_write(XBT_NIL, dev->nodename, "opened", "0"); + if (err) + goto fail; + err = xenbus_switch_state(dev, XenbusStateInitWait); if (err) goto fail; @@ -826,6 +848,19 @@ static void backend_changed(struct xenbus_watch *watch, goto fail; } + /* + * Tell userspace that the device has been opened and that blkback has a + * reference to it. Userspace can then close the device or mark it as + * delete-on-close, knowing that blkback will keep the device open as + * long as necessary. + */ + err = xenbus_write(XBT_NIL, dev->nodename, "opened", "1"); + if (err) { + xenbus_dev_fatal(dev, err, "%s: notifying userspace device has been opened", + dev->nodename); + goto free_vbd; + } + err = xenvbd_sysfs_addif(dev); if (err) { xenbus_dev_fatal(dev, err, "creating sysfs entries");
Set "opened" to "0" before the hotplug script is called. Once the device node has been opened, set "opened" to "1". "opened" is used exclusively by userspace. It serves two purposes: 1. It tells userspace that the diskseq Xenstore entry is supported. 2. It tells userspace that it can wait for "opened" to be set to 1. Once "opened" is 1, blkback has a reference to the device, so userspace doesn't need to keep one. Together, these changes allow userspace to use block devices with delete-on-close behavior, such as loop devices with the autoclear flag set. Signed-off-by: Demi Marie Obenour <demi@invisiblethingslab.com> --- drivers/block/xen-blkback/xenbus.c | 35 ++++++++++++++++++++++++++++++ 1 file changed, 35 insertions(+)