[PATCH v3 1/1] usertools/devbind: allow changing UID/GID for VFIO

[Anatoly Burakov <anatoly.burakov@intel.com>]

Currently, when binding a device to VFIO, the UID/GID for the device will
always stay as system default (`root`). Yet, when running DPDK as non-root
user, one has to change the UID/GID of the device to match the user's
UID/GID to use the device.

This patch adds an option to `dpdk-devbind.py` to change the UID/GID of
the device when binding it to VFIO.

Signed-off-by: Anatoly Burakov <anatoly.burakov@intel.com>
---

Notes:
    v2 -> v3:
    - Replaced error printout back to hard exit
    - Reworked UID/GID validation to be at command line parsing
    - Simplified chown code
    
    v1 -> v2:
    - Replaced hard exit with an error printout

 usertools/dpdk-devbind.py | 41 ++++++++++++++++++++++++++++++++++++---
 1 file changed, 38 insertions(+), 3 deletions(-)

diff --git a/usertools/dpdk-devbind.py b/usertools/dpdk-devbind.py
index f2a2a9a12f..ed1ef0cabc 100755
--- a/usertools/dpdk-devbind.py
+++ b/usertools/dpdk-devbind.py
@@ -3,11 +3,13 @@
 # Copyright(c) 2010-2014 Intel Corporation
 #
 
-import sys
-import os
-import subprocess
 import argparse
+import grp
+import os
 import platform
+import pwd
+import subprocess
+import sys
 
 from glob import glob
 from os.path import exists, basename
@@ -108,6 +110,8 @@
 status_flag = False
 force_flag = False
 noiommu_flag = False
+vfio_uid = -1
+vfio_gid = -1
 args = []
 
 
@@ -544,6 +548,19 @@ def bind_all(dev_list, driver, force=False):
 
     for d in dev_list:
         bind_one(d, driver, force)
+        # if we're binding to vfio-pci, set the IOMMU user/group ownership if one was specified
+        if driver == "vfio-pci" and (vfio_uid != -1 or vfio_gid != -1):
+            # find IOMMU group for a particular PCI device
+            iommu_grp_base_path = os.path.join("/sys/bus/pci/devices", d, "iommu_group")
+            # extract the IOMMU group number
+            iommu_grp = os.path.basename(os.readlink(iommu_grp_base_path))
+            # find VFIO device correspondiong to this IOMMU group
+            dev_path = os.path.join("/dev/vfio", iommu_grp)
+            # set ownership
+            try:
+                os.chown(dev_path, vfio_uid, vfio_gid)
+            except OSError as err:
+                sys.exit(f"Error: failed to set IOMMU group ownership for {d}: {err}")
 
     # For kernels < 3.15 when binding devices to a generic driver
     # (i.e. one that doesn't have a PCI ID table) using new_id, some devices
@@ -697,6 +714,8 @@ def parse_args():
     global force_flag
     global noiommu_flag
     global args
+    global vfio_uid
+    global vfio_gid
 
     parser = argparse.ArgumentParser(
         description='Utility to bind and unbind devices from Linux kernel',
@@ -746,6 +765,20 @@ def parse_args():
         '--noiommu-mode',
         action='store_true',
         help="If IOMMU is not available, enable no IOMMU mode for VFIO drivers")
+    parser.add_argument(
+        "-U",
+        "--uid",
+        help="For VFIO, specify the UID to set IOMMU group ownership",
+        type=lambda u: pwd.getpwnam(u).pw_uid,
+        default=-1,
+    )
+    parser.add_argument(
+        "-G",
+        "--gid",
+        help="For VFIO, specify the GID to set IOMMU group ownership",
+        type=lambda g: grp.getgrnam(g).gr_gid,
+        default=-1,
+    )
     parser.add_argument(
         '--force',
         action='store_true',
@@ -778,6 +811,8 @@ def parse_args():
         b_flag = opt.bind
     elif opt.unbind:
         b_flag = "none"
+    vfio_uid = opt.uid
+    vfio_gid = opt.gid
     args = opt.devices
 
     if not b_flag and not status_flag:
-- 
2.43.5