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Subject[PATCH 2/5] vmbus: add driver_override support
Date
From: Stephen Hemminger <stephen@networkplumber.org>

Add support for overriding the default driver for a VMBus device
in the same way that it can be done for PCI devices. This patch
adds the /sys/bus/vmbus/devices/.../driver_override file
and the logic for matching.

This is used by driverctl tool to do driver override.
https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgitlab.com%2Fdriverctl%2Fdriverctl&amp;data=02%7C01%7Ckys%40microsoft.com%7C42e803feb2c544ef6ea908d5fd538878%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C636693457619960040&amp;sdata=kEyYHRIjNZCk%2B37moCSqbrZL426YccNQrsWpENcrZdw%3D&amp;reserved=0

Signed-off-by: Stephen Hemminger <sthemmin@microsoft.com>
Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
---
Documentation/ABI/testing/sysfs-bus-vmbus | 21 ++++
drivers/hv/vmbus_drv.c | 115 ++++++++++++++++++----
include/linux/hyperv.h | 1 +
3 files changed, 118 insertions(+), 19 deletions(-)
create mode 100644 Documentation/ABI/testing/sysfs-bus-vmbus

diff --git a/Documentation/ABI/testing/sysfs-bus-vmbus b/Documentation/ABI/testing/sysfs-bus-vmbus
new file mode 100644
index 000000000000..91e6c065973c
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-bus-vmbus
@@ -0,0 +1,21 @@
+What: /sys/bus/vmbus/devices/.../driver_override
+Date: August 2019
+Contact: Stephen Hemminger <sthemmin@microsoft.com>
+Description:
+ This file allows the driver for a device to be specified which
+ will override standard static and dynamic ID matching. When
+ specified, only a driver with a name matching the value written
+ to driver_override will have an opportunity to bind to the
+ device. The override is specified by writing a string to the
+ driver_override file (echo uio_hv_generic > driver_override) and
+ may be cleared with an empty string (echo > driver_override).
+ This returns the device to standard matching rules binding.
+ Writing to driver_override does not automatically unbind the
+ device from its current driver or make any attempt to
+ automatically load the specified driver. If no driver with a
+ matching name is currently loaded in the kernel, the device
+ will not bind to any driver. This also allows devices to
+ opt-out of driver binding using a driver_override name such as
+ "none". Only a single driver may be specified in the override,
+ there is no support for parsing delimiters.
+
diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
index b1b548a21f91..e6d8fdac6d8b 100644
--- a/drivers/hv/vmbus_drv.c
+++ b/drivers/hv/vmbus_drv.c
@@ -498,6 +498,54 @@ static ssize_t device_show(struct device *dev,
}
static DEVICE_ATTR_RO(device);

+static ssize_t driver_override_store(struct device *dev,
+ struct device_attribute *attr,
+ const char *buf, size_t count)
+{
+ struct hv_device *hv_dev = device_to_hv_device(dev);
+ char *driver_override, *old, *cp;
+
+ /* We need to keep extra room for a newline */
+ if (count >= (PAGE_SIZE - 1))
+ return -EINVAL;
+
+ driver_override = kstrndup(buf, count, GFP_KERNEL);
+ if (!driver_override)
+ return -ENOMEM;
+
+ cp = strchr(driver_override, '\n');
+ if (cp)
+ *cp = '\0';
+
+ device_lock(dev);
+ old = hv_dev->driver_override;
+ if (strlen(driver_override)) {
+ hv_dev->driver_override = driver_override;
+ } else {
+ kfree(driver_override);
+ hv_dev->driver_override = NULL;
+ }
+ device_unlock(dev);
+
+ kfree(old);
+
+ return count;
+}
+
+static ssize_t driver_override_show(struct device *dev,
+ struct device_attribute *attr, char *buf)
+{
+ struct hv_device *hv_dev = device_to_hv_device(dev);
+ ssize_t len;
+
+ device_lock(dev);
+ len = snprintf(buf, PAGE_SIZE, "%s\n", hv_dev->driver_override);
+ device_unlock(dev);
+
+ return len;
+}
+static DEVICE_ATTR_RW(driver_override);
+
/* Set up per device attributes in /sys/bus/vmbus/devices/<bus device> */
static struct attribute *vmbus_dev_attrs[] = {
&dev_attr_id.attr,
@@ -528,6 +576,7 @@ static struct attribute *vmbus_dev_attrs[] = {
&dev_attr_channel_vp_mapping.attr,
&dev_attr_vendor.attr,
&dev_attr_device.attr,
+ &dev_attr_driver_override.attr,
NULL,
};
ATTRIBUTE_GROUPS(vmbus_dev);
@@ -563,17 +612,26 @@ static inline bool is_null_guid(const uuid_le *guid)
return true;
}

-/*
- * Return a matching hv_vmbus_device_id pointer.
- * If there is no match, return NULL.
- */
-static const struct hv_vmbus_device_id *hv_vmbus_get_id(struct hv_driver *drv,
- const uuid_le *guid)
+static const struct hv_vmbus_device_id *
+hv_vmbus_dev_match(const struct hv_vmbus_device_id *id, const uuid_le *guid)
+
+{
+ if (id == NULL)
+ return NULL; /* empty device table */
+
+ for (; !is_null_guid(&id->guid); id++)
+ if (!uuid_le_cmp(id->guid, *guid))
+ return id;
+
+ return NULL;
+}
+
+static const struct hv_vmbus_device_id *
+hv_vmbus_dynid_match(struct hv_driver *drv, const uuid_le *guid)
{
const struct hv_vmbus_device_id *id = NULL;
struct vmbus_dynid *dynid;

- /* Look at the dynamic ids first, before the static ones */
spin_lock(&drv->dynids.lock);
list_for_each_entry(dynid, &drv->dynids.list, node) {
if (!uuid_le_cmp(dynid->id.guid, *guid)) {
@@ -583,18 +641,37 @@ static const struct hv_vmbus_device_id *hv_vmbus_get_id(struct hv_driver *drv,
}
spin_unlock(&drv->dynids.lock);

- if (id)
- return id;
+ return id;
+}

- id = drv->id_table;
- if (id == NULL)
- return NULL; /* empty device table */
+static const struct hv_vmbus_device_id vmbus_device_null = {
+ .guid = NULL_UUID_LE,
+};

- for (; !is_null_guid(&id->guid); id++)
- if (!uuid_le_cmp(id->guid, *guid))
- return id;
+/*
+ * Return a matching hv_vmbus_device_id pointer.
+ * If there is no match, return NULL.
+ */
+static const struct hv_vmbus_device_id *hv_vmbus_get_id(struct hv_driver *drv,
+ struct hv_device *dev)
+{
+ const uuid_le *guid = &dev->dev_type;
+ const struct hv_vmbus_device_id *id;

- return NULL;
+ /* When driver_override is set, only bind to the matching driver */
+ if (dev->driver_override && strcmp(dev->driver_override, drv->name))
+ return NULL;
+
+ /* Look at the dynamic ids first, before the static ones */
+ id = hv_vmbus_dynid_match(drv, guid);
+ if (!id)
+ id = hv_vmbus_dev_match(drv->id_table, guid);
+
+ /* driver_override will always match, send a dummy id */
+ if (!id && dev->driver_override)
+ id = &vmbus_device_null;
+
+ return id;
}

/* vmbus_add_dynid - add a new device ID to this driver and re-probe devices */
@@ -643,7 +720,7 @@ static ssize_t new_id_store(struct device_driver *driver, const char *buf,
if (retval)
return retval;

- if (hv_vmbus_get_id(drv, &guid))
+ if (hv_vmbus_dynid_match(drv, &guid))
return -EEXIST;

retval = vmbus_add_dynid(drv, &guid);
@@ -708,7 +785,7 @@ static int vmbus_match(struct device *device, struct device_driver *driver)
if (is_hvsock_channel(hv_dev->channel))
return drv->hvsock;

- if (hv_vmbus_get_id(drv, &hv_dev->dev_type))
+ if (hv_vmbus_get_id(drv, hv_dev))
return 1;

return 0;
@@ -725,7 +802,7 @@ static int vmbus_probe(struct device *child_device)
struct hv_device *dev = device_to_hv_device(child_device);
const struct hv_vmbus_device_id *dev_id;

- dev_id = hv_vmbus_get_id(drv, &dev->dev_type);
+ dev_id = hv_vmbus_get_id(drv, dev);
if (drv->probe) {
ret = drv->probe(dev, dev_id);
if (ret != 0)
diff --git a/include/linux/hyperv.h b/include/linux/hyperv.h
index efda23cf32c7..2c3798bcb01c 100644
--- a/include/linux/hyperv.h
+++ b/include/linux/hyperv.h
@@ -1125,6 +1125,7 @@ struct hv_device {
u16 device_id;

struct device device;
+ char *driver_override; /* Driver name to force a match */

struct vmbus_channel *channel;
struct kset *channels_kset;
--
2.18.0
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