IB/uverbs: Increase maximum devices supported

Some large systems may support more than IB_UVERBS_MAX_DEVICES
(currently 32).

This change allows us to support more devices in a backwards-compatible
manner.  The first IB_UVERBS_MAX_DEVICES keep the same major/minor
device numbers that they've always had.

If there are more than IB_UVERBS_MAX_DEVICES, we then dynamically
request a new major device number (new minors start at 0).

This change increases the maximum number of HCAs to 64 (from 32).

Signed-off-by: Alex Chiang <achiang@hp.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>

1 files changed, 50 insertions, 6 deletions

diff --git a/drivers/infiniband/core/uverbs_main.c b/drivers/infiniband/core/uverbs_main.c
index 8c594cde8a1d..7d42d550e87e 100644
--- a/drivers/infiniband/core/uverbs_main.c
+++ b/drivers/infiniband/core/uverbs_main.c
@@ -728,6 +728,34 @@ static ssize_t show_abi_version(struct class *class, char *buf)
 }
 static CLASS_ATTR(abi_version, S_IRUGO, show_abi_version, NULL);
 
+static dev_t overflow_maj;
+static DECLARE_BITMAP(overflow_map, IB_UVERBS_MAX_DEVICES);
+
+/*
+ * If we have more than IB_UVERBS_MAX_DEVICES, dynamically overflow by
+ * requesting a new major number and doubling the number of max devices we
+ * support. It's stupid, but simple.
+ */
+static int find_overflow_devnum(void)
+{
+        int ret;
+
+        if (!overflow_maj) {
+                ret = alloc_chrdev_region(&overflow_maj, 0, IB_UVERBS_MAX_DEVICES,
+                                          "infiniband_verbs");
+                if (ret) {
+                        printk(KERN_ERR "user_verbs: couldn't register dynamic device number\n");
+                        return ret;
+                }
+        }
+
+        ret = find_first_zero_bit(overflow_map, IB_UVERBS_MAX_DEVICES);
+        if (ret >= IB_UVERBS_MAX_DEVICES)
+                return -1;
+
+        return ret;
+}
+
 static void ib_uverbs_add_one(struct ib_device *device)
 {
         int devnum;
@@ -748,11 +776,19 @@ static void ib_uverbs_add_one(struct ib_device *device)
         devnum = find_first_zero_bit(dev_map, IB_UVERBS_MAX_DEVICES);
         if (devnum >= IB_UVERBS_MAX_DEVICES) {
                 spin_unlock(&map_lock);
-                goto err;
+                devnum = find_overflow_devnum();
+                if (devnum < 0)
+                        goto err;
+
+                spin_lock(&map_lock);
+                uverbs_dev->devnum = devnum + IB_UVERBS_MAX_DEVICES;
+                base = devnum + overflow_maj;
+                set_bit(devnum, overflow_map);
+        } else {
+                uverbs_dev->devnum = devnum;
+                base = devnum + IB_UVERBS_BASE_DEV;
+                set_bit(devnum, dev_map);
         }
-        uverbs_dev->devnum = devnum;
-        base = devnum + IB_UVERBS_BASE_DEV;
-        set_bit(devnum, dev_map);
         spin_unlock(&map_lock);
 
         uverbs_dev->ib_dev           = device;
@@ -785,7 +821,10 @@ err_class:
 
 err_cdev:
         cdev_del(&uverbs_dev->cdev);
-        clear_bit(devnum, dev_map);
+        if (uverbs_dev->devnum < IB_UVERBS_MAX_DEVICES)
+                clear_bit(devnum, dev_map);
+        else
+                clear_bit(devnum, overflow_map);
 
 err:
         kref_put(&uverbs_dev->ref, ib_uverbs_release_dev);
@@ -805,7 +844,10 @@ static void ib_uverbs_remove_one(struct ib_device *device)
         device_destroy(uverbs_class, uverbs_dev->cdev.dev);
         cdev_del(&uverbs_dev->cdev);
 
-        clear_bit(uverbs_dev->devnum, dev_map);
+        if (uverbs_dev->devnum < IB_UVERBS_MAX_DEVICES)
+                clear_bit(uverbs_dev->devnum, dev_map);
+        else
+                clear_bit(uverbs_dev->devnum - IB_UVERBS_MAX_DEVICES, overflow_map);
 
         kref_put(&uverbs_dev->ref, ib_uverbs_release_dev);
         wait_for_completion(&uverbs_dev->comp);
@@ -895,6 +937,8 @@ static void __exit ib_uverbs_cleanup(void)
         unregister_filesystem(&uverbs_event_fs);
         class_destroy(uverbs_class);
         unregister_chrdev_region(IB_UVERBS_BASE_DEV, IB_UVERBS_MAX_DEVICES);
+        if (overflow_maj)
+                unregister_chrdev_region(overflow_maj, IB_UVERBS_MAX_DEVICES);
         idr_destroy(&ib_uverbs_pd_idr);
         idr_destroy(&ib_uverbs_mr_idr);
         idr_destroy(&ib_uverbs_mw_idr);