From: Demi Marie Obenour <demi@invisiblethingslab.com>
To: "Jens Axboe" <axboe@kernel.dk>,
"Roger Pau Monné" <roger.pau@citrix.com>,
"Juergen Gross" <jgross@suse.com>
Cc: "Demi Marie Obenour" <demi@invisiblethingslab.com>,
"Marek Marczykowski-Górecki" <marmarek@invisiblethingslab.com>,
xen-devel@lists.xenproject.org, linux-block@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: [RFC PATCH 7/7] xen/blkback: Inform userspace that device has been opened
Date: Wed, 25 Jan 2023 22:33:58 -0500 [thread overview]
Message-ID: <20230126033358.1880-7-demi@invisiblethingslab.com> (raw)
In-Reply-To: <20230126033358.1880-1-demi@invisiblethingslab.com>
This allows userspace to use block devices with delete-on-close
behavior, which is necessary to ensure virtual devices (such as loop or
device-mapper devices) are cleaned up automatically. Protocol details
are included in comments.
Signed-off-by: Demi Marie Obenour <demi@invisiblethingslab.com>
---
drivers/block/xen-blkback/xenbus.c | 34 ++++++++++++++++++++++++++++++
1 file changed, 34 insertions(+)
diff --git a/drivers/block/xen-blkback/xenbus.c b/drivers/block/xen-blkback/xenbus.c
index 2c43bfc7ab5ba6954f11d4b949a5668660dbd290..ca8dae05985038da490c5ac93364509913f6b4c7 100644
--- a/drivers/block/xen-blkback/xenbus.c
+++ b/drivers/block/xen-blkback/xenbus.c
@@ -3,6 +3,19 @@
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 used 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. Once
+ "opened" is 1, blkback has a reference to the device, so userspace doesn't
+ need to keep one.
*/
@@ -698,6 +711,14 @@ 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;
@@ -824,6 +845,19 @@ 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");
--
Sincerely,
Demi Marie Obenour (she/her/hers)
Invisible Things Lab
next prev parent reply other threads:[~2023-01-26 3:34 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-01-26 3:33 [RFC PATCH 0/7] Allow race-free block device handling Demi Marie Obenour
2023-01-26 3:33 ` [RFC PATCH 1/7] block: Support creating a struct file from a block device Demi Marie Obenour
2023-01-30 8:08 ` Christoph Hellwig
2023-01-30 19:22 ` Demi Marie Obenour
2023-01-31 8:53 ` Christoph Hellwig
2023-01-31 16:27 ` Demi Marie Obenour
2023-02-01 7:45 ` Christoph Hellwig
2023-02-01 16:18 ` Demi Marie Obenour
2023-02-02 8:49 ` Ming Lei
2023-02-02 17:24 ` Demi Marie Obenour
2023-01-26 3:33 ` [RFC PATCH 2/7] Allow userspace to get an FD to a newly-created DM device Demi Marie Obenour
2023-01-26 3:33 ` [RFC PATCH 3/7] Implement diskseq checks in blkback Demi Marie Obenour
2023-01-26 3:33 ` [RFC PATCH 4/7] Increment diskseq when releasing a loop device Demi Marie Obenour
2023-01-30 8:09 ` Christoph Hellwig
2023-01-26 3:33 ` [RFC PATCH 6/7] Minor blkback cleanups Demi Marie Obenour
2023-01-26 3:33 ` Demi Marie Obenour [this message]
2023-02-02 16:50 ` [RFC PATCH 0/7] Allow race-free block device handling Mike Snitzer
2023-02-02 18:41 ` Demi Marie Obenour
2023-02-02 19:56 ` Mike Snitzer
2023-02-02 20:57 ` Demi Marie Obenour
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