iommu: Add a function to find an iommu group by id

As IOMMU groups are exposed to the user space by their numbers,
the user space can use them in various kernel APIs so the kernel
might need an API to find a group by its ID.

As an example, QEMU VFIO on PPC64 platform needs it to associate
a logical bus number (LIOBN) with a specific IOMMU group in order
to support in-kernel handling of DMA map/unmap requests.

The patch adds the iommu_group_get_by_id(id) function which performs
such search.

v2: fixed reference counting.

Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Acked-by: Alex Williamson <alex.williamson@redhat.com>
Signed-off-by: Joerg Roedel <joro@8bytes.org>

diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
index b972d430d92b946eb16e98a41a2e23441b17f93e..db01af01ce0af6d60671d0ffbcf8982fd62f8367 100644 (file)
--- a/drivers/iommu/iommu.c
+++ b/drivers/iommu/iommu.c
@@ -204,6 +204,35 @@ again:
 }
 EXPORT_SYMBOL_GPL(iommu_group_alloc);
 
+struct iommu_group *iommu_group_get_by_id(int id)
+{
+       struct kobject *group_kobj;
+       struct iommu_group *group;
+       const char *name;
+
+       if (!iommu_group_kset)
+               return NULL;
+
+       name = kasprintf(GFP_KERNEL, "%d", id);
+       if (!name)
+               return NULL;
+
+       group_kobj = kset_find_obj(iommu_group_kset, name);
+       kfree(name);
+
+       if (!group_kobj)
+               return NULL;
+
+       group = container_of(group_kobj, struct iommu_group, kobj);
+       BUG_ON(group->id != id);
+
+       kobject_get(group->devices_kobj);
+       kobject_put(&group->kobj);
+
+       return group;
+}
+EXPORT_SYMBOL_GPL(iommu_group_get_by_id);
+
 /**
  * iommu_group_get_iommudata - retrieve iommu_data registered for a group
  * @group: the group

diff --git a/include/linux/iommu.h b/include/linux/iommu.h
index 6a027dc8dbfe7b46643072f36116338974457d8e..8e1b5be72b02eacdd9ac69f5904ad32d22ce99ca 100644 (file)
--- a/include/linux/iommu.h
+++ b/include/linux/iommu.h
@@ -126,6 +126,7 @@ struct iommu_ops {
 extern int bus_set_iommu(struct bus_type *bus, struct iommu_ops *ops);
 extern bool iommu_present(struct bus_type *bus);
 extern struct iommu_domain *iommu_domain_alloc(struct bus_type *bus);
+extern struct iommu_group *iommu_group_get_by_id(int id);
 extern void iommu_domain_free(struct iommu_domain *domain);
 extern int iommu_attach_device(struct iommu_domain *domain,
                               struct device *dev);