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Re: [libvirt] [PATCH 1/2] nodedev: sysfs: Set PCI_PHYSICAL_FUNCTION flag more carefully



On 05/23/2016 07:53 AM, Andrea Bolognani wrote:
The flag was set if virPCIGetPhysicalFunction() did not return
an error; unfortunately, the 'physfn' sysfs file not being
present is not considered an error, which means that the flag
was set pretty much unconditionally.

This behavior is the result of commit c8b1a83605:

  https://www.redhat.com/archives/libvir-list/2016-May/msg01348.html

Prior to this, virPCIGetPhysicalFunction had returned the return value from virPCIGetDeviceAddressFromSysfsLink(), which would be -1 if the physfn file didn't exist. That patch discards the return value and hardcodes a "return 0".

I think that virPCIGetPhysicalFunction should be restored to its original glory (No, I didn't write it). Either that, or the other caller to virPCIGetPhysicalFunction (virPCIGetVirtualFunctionInfo) should also be fixed so that it doesn't crash due to the changed semantics of virPCIGetPhysicalFunction.

(A more correct fix may be to change the semantics of virPCIGetPhysicalFunction() to return -1 only in the case of a bonafide error (OOM, failure to parse the contents of an existing physfn file), but that would also require modifying virPCIGetDeviceAddressFromSysfsLink() to return 0/-1 rather than a virPCIDeviceAddresPtr so that we can tell the difference between "no physfn" and "there was a physfn but I encountered some other error". In other words - 1) revert commit c1faf309 (part of the same "coverity fixes" series as x8b1a83605), then 2) adjust the function to set *bdf = 0 and return 0 when the physfn file doesn't exist.)



This, in turn, caused libvirtd to crash in
virNodeDeviceDefFormat(), where the presence of the flag
is considered a reliable indicator of the fact that
pci_dev.physical_function has been filled in.

Change the code to check pci_dev.physical_function before
setting the flag.
---
  src/node_device/node_device_linux_sysfs.c | 10 ++++++++--
  1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/src/node_device/node_device_linux_sysfs.c b/src/node_device/node_device_linux_sysfs.c
index 24a6a2e..b337d2d 100644
--- a/src/node_device/node_device_linux_sysfs.c
+++ b/src/node_device/node_device_linux_sysfs.c
@@ -154,19 +154,25 @@ nodeDeviceSysfsGetPCISRIOVCaps(const char *sysfsPath,
      data->pci_dev.flags &= ~VIR_NODE_DEV_CAP_FLAG_PCI_VIRTUAL_FUNCTION;
      data->pci_dev.flags &= ~VIR_NODE_DEV_CAP_FLAG_PCI_PHYSICAL_FUNCTION;
- if (!virPCIGetPhysicalFunction(sysfsPath, &data->pci_dev.physical_function))
+    ret = virPCIGetPhysicalFunction(sysfsPath,
+                                    &data->pci_dev.physical_function);
+    if (ret < 0)
+        goto out;
+
+    if (data->pci_dev.physical_function)
          data->pci_dev.flags |= VIR_NODE_DEV_CAP_FLAG_PCI_PHYSICAL_FUNCTION;
ret = virPCIGetVirtualFunctions(sysfsPath, &data->pci_dev.virtual_functions,
                                      &data->pci_dev.num_virtual_functions,
                                      &data->pci_dev.max_virtual_functions);
      if (ret < 0)
-        return ret;
+        goto out;
if (data->pci_dev.num_virtual_functions > 0 ||
          data->pci_dev.max_virtual_functions > 0)
          data->pci_dev.flags |= VIR_NODE_DEV_CAP_FLAG_PCI_VIRTUAL_FUNCTION;
+ out:
      return ret;
  }



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