Re: [Qemu-devel] [PATCH v4 15/17] vfio/pci: Remove vfio_msix_early_setup returned value

[Auger Eric]

Hi Markus,

On 04/10/2016 15:05, Markus Armbruster wrote:
> Eric Auger <address@hidden> writes:
> 
>> The returned value is not used anymore by the caller, vfio_realize,
>> since the error now is stored in the error object. So let's remove it.
>>
>> Signed-off-by: Eric Auger <address@hidden>
>>
>> ---
>>
>> Logically we could do that job for all the functions now getting an
>> Error object passed as a parameter to avoid duplicate information
>> between the error content and the returned value. This requires to use
>> a local error object in vfio_realize. So I am not sure this is worth
>> the candle.
> 
> Matter of taste, yours is fine.
> 
> We used to recommend returing void instead of an error code when the
> function sets and error.  More parsimonious in theory, more boiler-plate
> in practice, so we accept either now.  Perhaps we should even recommend
> returning an error code, but such a recommendation needs to come with
> patches converting existing code to it.

The risk is that if a programmer returns an error value without setting
the errp he will get a sigsev on subsequent error_prepend().
> 
>> ---
>>  hw/vfio/pci.c | 20 ++++++++++----------
>>  1 file changed, 10 insertions(+), 10 deletions(-)
>>
>> diff --git a/hw/vfio/pci.c b/hw/vfio/pci.c
>> index b316e13..cea4d48 100644
>> --- a/hw/vfio/pci.c
>> +++ b/hw/vfio/pci.c
>> @@ -1290,7 +1290,7 @@ static void vfio_pci_fixup_msix_region(VFIOPCIDevice 
>> *vdev)
>>   * need to first look for where the MSI-X table lives.  So we
>>   * unfortunately split MSI-X setup across two functions.
>>   */
>> -static int vfio_msix_early_setup(VFIOPCIDevice *vdev, Error **errp)
>> +static void vfio_msix_early_setup(VFIOPCIDevice *vdev, Error **errp)
>>  {
>>      uint8_t pos;
>>      uint16_t ctrl;
>> @@ -1300,25 +1300,25 @@ static int vfio_msix_early_setup(VFIOPCIDevice 
>> *vdev, Error **errp)
>>  
>>      pos = pci_find_capability(&vdev->pdev, PCI_CAP_ID_MSIX);
>>      if (!pos) {
>> -        return 0;
>> +        return;
>>      }
>>  
>>      if (pread(fd, &ctrl, sizeof(ctrl),
>>                vdev->config_offset + pos + PCI_MSIX_FLAGS) != sizeof(ctrl)) {
>>          error_setg_errno(errp, errno, "failed to read PCI MSIX FLAGS");
>> -        return -errno;
>> +        return;
>>      }
>>  
>>      if (pread(fd, &table, sizeof(table),
>>                vdev->config_offset + pos + PCI_MSIX_TABLE) != sizeof(table)) 
>> {
>>          error_setg_errno(errp, errno, "failed to read PCI MSIX TABLE");
>> -        return -errno;
>> +        return;
>>      }
>>  
>>      if (pread(fd, &pba, sizeof(pba),
>>                vdev->config_offset + pos + PCI_MSIX_PBA) != sizeof(pba)) {
>>          error_setg_errno(errp, errno, "failed to read PCI MSIX PBA");
>> -        return -errno;
>> +        return;
>>      }
>>  
>>      ctrl = le16_to_cpu(ctrl);
>> @@ -1351,7 +1351,7 @@ static int vfio_msix_early_setup(VFIOPCIDevice *vdev, 
>> Error **errp)
>>              error_setg(errp, "hardware reports invalid configuration, "
>>                         "MSIX PBA outside of specified BAR");
>>              g_free(msix);
>> -            return -EINVAL;
>> +            return;
>>          }
>>      }
>>  
>> @@ -1360,8 +1360,6 @@ static int vfio_msix_early_setup(VFIOPCIDevice *vdev, 
>> Error **errp)
>>      vdev->msix = msix;
>>  
>>      vfio_pci_fixup_msix_region(vdev);
>> -
>> -    return 0;
>>  }
>>  
>>  static int vfio_msix_setup(VFIOPCIDevice *vdev, int pos, Error **errp)
>> @@ -2519,6 +2517,7 @@ static void vfio_realize(PCIDevice *pdev, Error **errp)
>>      VFIODevice *vbasedev_iter;
>>      VFIOGroup *group;
>>      char *tmp, group_path[PATH_MAX], *group_name;
>> +    Error *err = NULL;
>>      ssize_t len;
>>      struct stat st;
>>      int groupid;
>> @@ -2670,8 +2669,9 @@ static void vfio_realize(PCIDevice *pdev, Error **errp)
>>  
>>      vfio_pci_size_rom(vdev);
>>  
>> -    ret = vfio_msix_early_setup(vdev, errp);
>> -    if (ret) {
>> +    vfio_msix_early_setup(vdev, &err);
>> +    if (err) {
>> +        error_propagate(errp, err);
>>          goto error;
>>      }
> 
> PATCH 04 checks err, PATCH 13 flips to ret, and this one flips back.
> Have you considered dropping both flips?  Your choice.
I removed one flip at least

Thanks

Eric
>