[RFC PATCH 06/13] iommufd: Expose persistent iommufd IDs in sysfs

James Gowans
2024-09-16T11:33:44Z

After kexec userspace needs the ability to re-acquire a handle to the
IOMMUFD which it was using before kexec. To provide userspace the
ability to discover persisted domains and get a handle to them, expose
all of the persisted IDs in sysfs. Each persisted ID will create a
directory like:
/sys/kernel/persisted_iommufd/<id>
In the next commit a file will be added to this directory to allow
actually restoring the IOMMUFD.
---
drivers/iommu/iommufd/serialise.c | 48 ++++++++++++++++++++++++++++++-
1 file changed, 47 insertions(+), 1 deletion(-)

diff --git a/drivers/iommu/iommufd/serialise.c b/drivers/iommu/iommufd/serialise.c
index 6b4c306dce40..7f2e7b1eda13 100644
--- a/drivers/iommu/iommufd/serialise.c
+++ b/drivers/iommu/iommufd/serialise.c
@@ -21,6 +21,9 @@
* }
* ]
*/
+
+static struct kobject *persisted_dir_kobj;
+
static int serialise_iommufd(void *fdt, struct iommufd_ctx *ictx)
{
int err = 0;
@@ -94,8 +97,51 @@ int iommufd_serialise_kho(struct notifier_block *self, unsigned long cmd,
}
}

+static ssize_t iommufd_show(struct kobject *kobj, struct kobj_attribute *attr,
+ char *buf)
+{
+ return 0;
+}
+
+static struct kobj_attribute persisted_attr =
+ __ATTR_RO_MODE(iommufd, 0440);
+
+static int deserialise_iommufds(const void *fdt, int root_off)
+{
+ int off;
+
+ /*
+ * For each persisted iommufd id, create a directory
+ * in sysfs with an iommufd file in it.
+ */
+ fdt_for_each_subnode(off, fdt, root_off) {
+ struct kobject *kobj;
+ const char *name = fdt_get_name(fdt, off, NULL);
+ int rc;
+
+ kobj = kobject_create_and_add(name, persisted_dir_kobj);
+ rc = sysfs_create_file(kobj, &persisted_attr.attr);
+ if (rc)
+ pr_warn("Unable to create sysfs file for iommufd node %s\n", name);
+ }
+ return 0;
+}
+
int __init iommufd_deserialise_kho(void)
{
- pr_info("would deserialise here\n");
+ const void *fdt = kho_get_fdt();
+ int off;
+
+ if (!fdt)
+ return 0;
+
+ /* Parent directory for persisted iommufd files. */
+ persisted_dir_kobj = kobject_create_and_add("iommufd_persisted", kernel_kobj);
+
+ off = fdt_path_offset(fdt, "/iommufd");
+ if (off <= 0)
+ return 0; /* No data in KHO */
+
+ deserialise_iommufds(fdt, fdt_subnode_offset(fdt, off, "iommufds"));
return 0;
}
--
2.34.1