virpci: introduce virPCIDeviceExists()

We're going to add logic to handle the case where a previously
existing PCI device does not longer exist in the host.

The logic was copied from virPCIDeviceNew(), which verifies if a
PCI device exists in the host, returning NULL and throwing an
error if it doesn't. The NULL is used for other errors as well
(product/vendor id read errors, dev id overflow), meaning that we
can't re-use virPCIDeviceNew() for the purpose of detecting
if the device exists.

Reviewed-by: Laine Stump <laine@redhat.com>
Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>

src/libvirt_private.syms

@@ -2924,6 +2924,7 @@ virPCIDeviceAddressIsValid;
 virPCIDeviceAddressParse;
 virPCIDeviceCopy;
 virPCIDeviceDetach;
+virPCIDeviceExists;
 virPCIDeviceFileIterate;
 virPCIDeviceFree;
 virPCIDeviceGetAddress;

src/util/virpci.c

@@ -1448,6 +1448,16 @@ virPCIDeviceAddressAsString(const virPCIDeviceAddress *addr)
     return str;
 }
 
+bool
+virPCIDeviceExists(const virPCIDeviceAddress *addr)
+{
+    g_autofree char *devName = virPCIDeviceAddressAsString(addr);
+    g_autofree char *devPath = g_strdup_printf(PCI_SYSFS "devices/%s/config",
+                                               devName);
+
+    return virFileExists(devPath);
+}
+
 virPCIDevicePtr
 virPCIDeviceNew(const virPCIDeviceAddress *address)
 {

src/util/virpci.h

@@ -206,6 +206,7 @@ int virPCIDeviceAddressGetIOMMUGroupAddresses(virPCIDeviceAddressPtr devAddr,
                                               size_t *nIommuGroupDevices);
 int virPCIDeviceAddressGetIOMMUGroupNum(virPCIDeviceAddressPtr addr);
 char *virPCIDeviceAddressGetIOMMUGroupDev(const virPCIDeviceAddress *devAddr);
+bool virPCIDeviceExists(const virPCIDeviceAddress *addr);
 char *virPCIDeviceGetIOMMUGroupDev(virPCIDevicePtr dev);
 
 int virPCIDeviceIsAssignable(virPCIDevicePtr dev,