These comments explain the difference between a virPCIDevice
instance used for lookups and an actual device instance; some
information is also provided for specific uses.
---
src/util/virhostdev.c | 38 ++++++++++++++++++++++++++++++++++++++
1 file changed, 38 insertions(+)
diff --git a/src/util/virhostdev.c b/src/util/virhostdev.c
index 10d1c1a..a431f0a 100644
--- a/src/util/virhostdev.c
+++ b/src/util/virhostdev.c
@@ -60,6 +60,27 @@ struct virHostdevIsPCINodeDeviceUsedData {
const bool usesVFIO;
};
+/* This module makes heavy use of bookkeeping lists, contained inside a
+ * virHostdevManager instance, to keep track of the devices' status. To make
+ * it easy to spot potential ownership errors when moving devices from one
+ * list to the other, variable names should comply with the following
+ * conventions when it comes to virPCIDevice and virPCIDeviceList instances:
+ *
+ * pci - a short-lived virPCIDevice whose purpose is usually just to look
+ * up the actual PCI device in one of the bookkeeping lists; basically
+ * little more than a fancy virPCIDeviceAddress
+ *
+ * pcidevs - a list containing a bunch of the above
+ *
+ * actual - a virPCIDevice instance that has either been retrieved from one
+ * of the bookkeeping lists, or is intended to be added or copied
+ * to one at some point
+ *
+ * Passing an 'actual' to a function that requires a 'pci' is fine, but the
+ * opposite is usually not true; as a rule of thumb, functions in the virpci
+ * module usually expect an 'actual'. Even with these conventions in place,
+ * adding comments to highlight ownership-related issues is recommended */
+
static int virHostdevIsPCINodeDeviceUsed(virPCIDeviceAddressPtr devAddr, void *opaque)
{
virPCIDevicePtr actual;
@@ -544,6 +565,10 @@ virHostdevPreparePCIDevices(virHostdevManagerPtr mgr,
virPCIDevicePtr pci = virPCIDeviceListGet(pcidevs, i);
if (virPCIDeviceGetManaged(pci)) {
+ /* We can't look up the actual device because it has not been
+ * created yet: virPCIDeviceDetach() will insert a copy of 'pci'
+ * into the list of inactive devices, and that copy will be the
+ * actual device going forward */
VIR_DEBUG("Detaching managed PCI device %s",
virPCIDeviceGetName(pci));
if (virPCIDeviceDetach(pci,
@@ -564,6 +589,9 @@ virHostdevPreparePCIDevices(virHostdevManagerPtr mgr,
for (i = 0; i < virPCIDeviceListCount(pcidevs); i++) {
virPCIDevicePtr pci = virPCIDeviceListGet(pcidevs, i);
+ /* We can avoid looking up the actual device here, because performing
+ * a PCI reset on a device doesn't require any information other than
+ * the address, which 'pci' already contains */
VIR_DEBUG("Resetting PCI device %s", virPCIDeviceGetName(pci));
if (virPCIDeviceReset(pci, mgr->activePCIHostdevs,
mgr->inactivePCIHostdevs) < 0)
@@ -608,6 +636,9 @@ virHostdevPreparePCIDevices(virHostdevManagerPtr mgr,
for (i = 0; i < virPCIDeviceListCount(pcidevs); i++) {
virPCIDevicePtr pci, actual;
+ /* We need to look up the actual device and set the information
+ * there because 'pci' only contain address information and will
+ * be released at the end of the function */
pci = virPCIDeviceListGet(pcidevs, i);
actual = virPCIDeviceListFind(mgr->activePCIHostdevs, pci);
@@ -775,6 +806,10 @@ virHostdevReAttachPCIDevices(virHostdevManagerPtr mgr,
virPCIDevicePtr pci = virPCIDeviceListGet(pcidevs, i);
virPCIDevicePtr actual = NULL;
+ /* We need to look up the actual device, which is the one containing
+ * information such as by which domain and driver it is used. As a
+ * side effect, by looking it up we can also tell whether it was
+ * really active in the first place */
actual = virPCIDeviceListFind(mgr->activePCIHostdevs, pci);
if (actual) {
const char *actual_drvname;
@@ -830,6 +865,9 @@ virHostdevReAttachPCIDevices(virHostdevManagerPtr mgr,
for (i = 0; i < virPCIDeviceListCount(pcidevs); i++) {
virPCIDevicePtr pci = virPCIDeviceListGet(pcidevs, i);
+ /* We can avoid looking up the actual device here, because performing
+ * a PCI reset on a device doesn't require any information other than
+ * the address, which 'pci' already contains */
VIR_DEBUG("Resetting PCI device %s", virPCIDeviceGetName(pci));
if (virPCIDeviceReset(pci, mgr->activePCIHostdevs,
mgr->inactivePCIHostdevs) < 0) {
--
2.5.0
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