From 7b752336bd26048514d55bb222531c0b0183fa9c Mon Sep 17 00:00:00 2001
From: Erik Skultety <eskultet@redhat.com>
Date: Thu, 7 Jan 2021 16:53:21 +0100
Subject: [PATCH 079/108] hostdev: mdev: Lookup mdevs by sysfs path rather than
 mdev struct
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The lookup didn't do anything apart from comparing the sysfs paths
anyway since that's what makes each mdev unique.
The most ridiculous usage of the old logic was in
virHostdevReAttachMediatedDevices where in order to drop an mdev
hostdev from the list of active devices we first had to create a new
mdev and use it in the lookup call. Why couldn't we have used the
hostdev directly? Because the hostdev and mdev structures are
incompatible.

The way mdevs are currently removed is via a write to a specific sysfs
attribute. If you do it while the machine which has the mdev assigned
is running, the write call may block (with a new enough kernel, with
older kernels it would return a write error!) until the device
is no longer in use which is when the QEMU process exits.

The interesting part here comes afterwards when we're cleaning up and
call virHostdevReAttachMediatedDevices. The domain doesn't exist
anymore, so the list of active hostdevs needs to be updated and the
respective hostdevs removed from the list, but remember we had to
create an mdev object in the memory in order to find it in the list
first which will fail because the write to sysfs had already removed
the mdev instance from the host system.
And so the next time you try to start the same domain you'll get:

"Requested operation is not valid: mediated device <path> is in use by
driver QEMU, domain <name>"

Fixes: https://gitlab.com/libvirt/libvirt/-/issues/119

Signed-off-by: Erik Skultety <eskultet@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>
(cherry picked from commit 49cb59778a4e6c2d04bb9383a9d97fbbc83f9fce)
---
 src/hypervisor/virhostdev.c | 10 ++++------
 src/util/virmdev.c          | 16 ++++++++--------
 src/util/virmdev.h          |  4 ++--
 3 files changed, 14 insertions(+), 16 deletions(-)

diff --git a/src/hypervisor/virhostdev.c b/src/hypervisor/virhostdev.c
index c88c8bee0e..4057f7b25f 100644
--- a/src/hypervisor/virhostdev.c
+++ b/src/hypervisor/virhostdev.c
@@ -1981,7 +1981,7 @@ virHostdevReAttachMediatedDevices(virHostdevManagerPtr mgr,
 
     virObjectLock(mgr->activeMediatedHostdevs);
     for (i = 0; i < nhostdevs; i++) {
-        g_autoptr(virMediatedDevice) mdev = NULL;
+        g_autofree char *sysfspath = NULL;
         virMediatedDevicePtr tmp;
         virDomainHostdevSubsysMediatedDevPtr mdevsrc;
         virDomainHostdevDefPtr hostdev = hostdevs[i];
@@ -1990,14 +1990,12 @@ virHostdevReAttachMediatedDevices(virHostdevManagerPtr mgr,
             continue;
 
         mdevsrc = &hostdev->source.subsys.u.mdev;
-
-        if (!(mdev = virMediatedDeviceNew(mdevsrc->uuidstr,
-                                          mdevsrc->model)))
-            continue;
+        sysfspath = virMediatedDeviceGetSysfsPath(mdevsrc->uuidstr);
 
         /* Remove from the list only mdevs assigned to @drv_name/@dom_name */
 
-        tmp = virMediatedDeviceListFind(mgr->activeMediatedHostdevs, mdev);
+        tmp = virMediatedDeviceListFind(mgr->activeMediatedHostdevs,
+                                        sysfspath);
 
         /* skip inactive devices */
         if (!tmp)
diff --git a/src/util/virmdev.c b/src/util/virmdev.c
index c2499c0a20..bae4a7d2c1 100644
--- a/src/util/virmdev.c
+++ b/src/util/virmdev.c
@@ -312,7 +312,7 @@ int
 virMediatedDeviceListAdd(virMediatedDeviceListPtr list,
                          virMediatedDevicePtr *dev)
 {
-    if (virMediatedDeviceListFind(list, *dev)) {
+    if (virMediatedDeviceListFind(list, (*dev)->path)) {
         virReportError(VIR_ERR_INTERNAL_ERROR,
                        _("device %s is already in use"), (*dev)->path);
         return -1;
@@ -358,7 +358,7 @@ virMediatedDevicePtr
 virMediatedDeviceListSteal(virMediatedDeviceListPtr list,
                            virMediatedDevicePtr dev)
 {
-    int idx = virMediatedDeviceListFindIndex(list, dev);
+    int idx = virMediatedDeviceListFindIndex(list, dev->path);
 
     return virMediatedDeviceListStealIndex(list, idx);
 }
@@ -374,13 +374,13 @@ virMediatedDeviceListDel(virMediatedDeviceListPtr list,
 
 int
 virMediatedDeviceListFindIndex(virMediatedDeviceListPtr list,
-                               virMediatedDevicePtr dev)
+                               const char *sysfspath)
 {
     size_t i;
 
     for (i = 0; i < list->count; i++) {
-        virMediatedDevicePtr other = list->devs[i];
-        if (STREQ(other->path, dev->path))
+        virMediatedDevicePtr dev = list->devs[i];
+        if (STREQ(sysfspath, dev->path))
             return i;
     }
     return -1;
@@ -389,11 +389,11 @@ virMediatedDeviceListFindIndex(virMediatedDeviceListPtr list,
 
 virMediatedDevicePtr
 virMediatedDeviceListFind(virMediatedDeviceListPtr list,
-                          virMediatedDevicePtr dev)
+                          const char *sysfspath)
 {
     int idx;
 
-    if ((idx = virMediatedDeviceListFindIndex(list, dev)) >= 0)
+    if ((idx = virMediatedDeviceListFindIndex(list, sysfspath)) >= 0)
         return list->devs[idx];
     else
         return NULL;
@@ -407,7 +407,7 @@ virMediatedDeviceIsUsed(virMediatedDevicePtr dev,
     const char *drvname, *domname;
     virMediatedDevicePtr tmp = NULL;
 
-    if ((tmp = virMediatedDeviceListFind(list, dev))) {
+    if ((tmp = virMediatedDeviceListFind(list, dev->path))) {
         virMediatedDeviceGetUsedBy(tmp, &drvname, &domname);
         virReportError(VIR_ERR_OPERATION_INVALID,
                        _("mediated device %s is in use by "
diff --git a/src/util/virmdev.h b/src/util/virmdev.h
index 51f7f608a2..1d97f7d44f 100644
--- a/src/util/virmdev.h
+++ b/src/util/virmdev.h
@@ -119,11 +119,11 @@ virMediatedDeviceListDel(virMediatedDeviceListPtr list,
 
 virMediatedDevicePtr
 virMediatedDeviceListFind(virMediatedDeviceListPtr list,
-                          virMediatedDevicePtr dev);
+                          const char *sysfspath);
 
 int
 virMediatedDeviceListFindIndex(virMediatedDeviceListPtr list,
-                               virMediatedDevicePtr dev);
+                               const char *sysfspath);
 
 int
 virMediatedDeviceListMarkDevices(virMediatedDeviceListPtr dst,
-- 
2.33.0

