Re: [Qemu-devel] [PATCH v2 01/12] vfio/pci: Use local error object in vfio_initfn

[Auger Eric]

Hi Markus,

On 22/09/2016 17:42, Markus Armbruster wrote:
> Eric Auger <address@hidden> writes:
> 
>> To prepare for migration to realize, let's use a local error
>> object in vfio_initfn. Also let's use the same error prefix for all
>> error messages.
>>
>> On top of the 1-1 conversion, we start using a common error prefix for
>> all error messages. We also introduce a similar warning prefix which will
>> be used later on.
>>
>> Signed-off-by: Eric Auger <address@hidden>
>> ---
>>
>> v2: creation
>> ---
>>  hw/vfio/pci.c                 | 73 
>> +++++++++++++++++++++++++------------------
>>  include/hw/vfio/vfio-common.h |  3 ++
>>  2 files changed, 46 insertions(+), 30 deletions(-)
>>
>> diff --git a/hw/vfio/pci.c b/hw/vfio/pci.c
>> index a5a620a..ca0293d 100644
>> --- a/hw/vfio/pci.c
>> +++ b/hw/vfio/pci.c
>> @@ -2493,6 +2493,7 @@ static int vfio_initfn(PCIDevice *pdev)
>>      VFIODevice *vbasedev_iter;
>>      VFIOGroup *group;
>>      char *tmp, group_path[PATH_MAX], *group_name;
>> +    Error *err = NULL;
>>      ssize_t len;
>>      struct stat st;
>>      int groupid;
>> @@ -2506,9 +2507,9 @@ static int vfio_initfn(PCIDevice *pdev)
>>      }
>>  
>>      if (stat(vdev->vbasedev.sysfsdev, &st) < 0) {
>> -        error_report("vfio: error: no such host device: %s",
>> -                     vdev->vbasedev.sysfsdev);
>> -        return -errno;
>> +        error_setg(&err, "no such host device");
> 
> Any particular reason you don't use error_setg_errno() here?
I hesitated and eventually removed into thinking it was not bringing
much value. But not strong opinion here, I will restore it.
> 
>> +        ret = -errno;
>> +        goto error;
>>      }
>>  
>>      vdev->vbasedev.name = g_strdup(basename(vdev->vbasedev.sysfsdev));
>> @@ -2520,40 +2521,44 @@ static int vfio_initfn(PCIDevice *pdev)
>>      g_free(tmp);
>>  
>>      if (len <= 0 || len >= sizeof(group_path)) {
>> -        error_report("vfio: error no iommu_group for device");
>> -        return len < 0 ? -errno : -ENAMETOOLONG;
>> +        error_setg_errno(&err, len < 0 ? errno : ENAMETOOLONG,
>> +                         "no iommu_group found");
>> +        ret = len < 0 ? -errno : -ENAMETOOLONG;
> 
> Suggest
> 
>            ret = len < 0 ? -errno : -ENAMETOOLONG;
>            error_setg_errno(&err, -ret, "no iommu_group found");
Sure. Eventually ret will disappear so we will come back to
error_setg_errno(&err, len < 0 ? errno : ENAMETOOLONG,
>> +                         "no iommu_group found");
> 
>> +        goto error;
>>      }
>>  
>>      group_path[len] = 0;
>>  
>>      group_name = basename(group_path);
>>      if (sscanf(group_name, "%d", &groupid) != 1) {
>> -        error_report("vfio: error reading %s: %m", group_path);
>> -        return -errno;
>> +        error_setg_errno(&err, errno, "failed to read %s", group_path);
>> +        ret = -errno;
>> +        goto error;
>>      }
>>  
>>      trace_vfio_initfn(vdev->vbasedev.name, groupid);
>>  
>>      group = vfio_get_group(groupid, pci_device_iommu_address_space(pdev));
>>      if (!group) {
>> -        error_report("vfio: failed to get group %d", groupid);
>> -        return -ENOENT;
>> +        error_setg(&err, "failed to get group %d", groupid);
>> +        ret = -ENOENT;
>> +        goto error;
>>      }
>>  
>>      QLIST_FOREACH(vbasedev_iter, &group->device_list, next) {
>>          if (strcmp(vbasedev_iter->name, vdev->vbasedev.name) == 0) {
>> -            error_report("vfio: error: device %s is already attached",
>> -                         vdev->vbasedev.name);
>> +            error_setg(&err, "device is already attached");
>>              vfio_put_group(group);
>> -            return -EBUSY;
>> +            ret = -EBUSY;
>> +            goto error;
>>          }
>>      }
>>  
>>      ret = vfio_get_device(group, vdev->vbasedev.name, &vdev->vbasedev);
>>      if (ret) {
>> -        error_report("vfio: failed to get device %s", vdev->vbasedev.name);
>> +        error_setg_errno(&err, -ret, "failed to get device");
>>          vfio_put_group(group);
>> -        return ret;
>> +        goto error;
>>      }
>>  
>>      ret = vfio_populate_device(vdev);
>> @@ -2567,8 +2572,8 @@ static int vfio_initfn(PCIDevice *pdev)
>>                  vdev->config_offset);
>>      if (ret < (int)MIN(pci_config_size(&vdev->pdev), vdev->config_size)) {
>>          ret = ret < 0 ? -errno : -EFAULT;
>> -        error_report("vfio: Failed to read device config space");
>> -        return ret;
>> +        error_setg_errno(&err, -ret, "failed to read device config space");
>> +        goto error;
>>      }
>>  
>>      /* vfio emulates a lot for us, but some bits need extra love */
>> @@ -2584,8 +2589,9 @@ static int vfio_initfn(PCIDevice *pdev)
>>       */
>>      if (vdev->vendor_id != PCI_ANY_ID) {
>>          if (vdev->vendor_id >= 0xffff) {
>> -            error_report("vfio: Invalid PCI vendor ID provided");
>> -            return -EINVAL;
>> +            error_setg(&err, "invalid PCI vendor ID provided");
>> +            ret = -EINVAL;
>> +            goto error;
>>          }
>>          vfio_add_emulated_word(vdev, PCI_VENDOR_ID, vdev->vendor_id, ~0);
>>          trace_vfio_pci_emulated_vendor_id(vdev->vbasedev.name, 
>> vdev->vendor_id);
>> @@ -2595,8 +2601,9 @@ static int vfio_initfn(PCIDevice *pdev)
>>  
>>      if (vdev->device_id != PCI_ANY_ID) {
>>          if (vdev->device_id > 0xffff) {
>> -            error_report("vfio: Invalid PCI device ID provided");
>> -            return -EINVAL;
>> +            error_setg(&err, "invalid PCI device ID provided");
>> +            ret = -EINVAL;
>> +            goto error;
>>          }
>>          vfio_add_emulated_word(vdev, PCI_DEVICE_ID, vdev->device_id, ~0);
>>          trace_vfio_pci_emulated_device_id(vdev->vbasedev.name, 
>> vdev->device_id);
>> @@ -2606,8 +2613,9 @@ static int vfio_initfn(PCIDevice *pdev)
>>  
>>      if (vdev->sub_vendor_id != PCI_ANY_ID) {
>>          if (vdev->sub_vendor_id > 0xffff) {
>> -            error_report("vfio: Invalid PCI subsystem vendor ID provided");
>> -            return -EINVAL;
>> +            error_setg(&err, "invalid PCI subsystem vendor ID provided");
>> +            ret = -EINVAL;
>> +            goto error;
>>          }
>>          vfio_add_emulated_word(vdev, PCI_SUBSYSTEM_VENDOR_ID,
>>                                 vdev->sub_vendor_id, ~0);
>> @@ -2617,8 +2625,9 @@ static int vfio_initfn(PCIDevice *pdev)
>>  
>>      if (vdev->sub_device_id != PCI_ANY_ID) {
>>          if (vdev->sub_device_id > 0xffff) {
>> -            error_report("vfio: Invalid PCI subsystem device ID provided");
>> -            return -EINVAL;
>> +            error_setg(&err, "invalid PCI subsystem device ID provided");
>> +            ret = -EINVAL;
>> +            goto error;
>>          }
>>          vfio_add_emulated_word(vdev, PCI_SUBSYSTEM_ID, vdev->sub_device_id, 
>> ~0);
>>          trace_vfio_pci_emulated_sub_device_id(vdev->vbasedev.name,
>> @@ -2671,8 +2680,9 @@ static int vfio_initfn(PCIDevice *pdev)
>>          struct vfio_region_info *opregion;
>>  
>>          if (vdev->pdev.qdev.hotplugged) {
>> -            error_report("Cannot support IGD OpRegion feature on hotplugged 
>> "
>> -                         "device %s", vdev->vbasedev.name);
>> +            error_setg(&err,
>> +                       "cannot support IGD OpRegion feature on hotplugged "
>> +                       "device");
>>              ret = -EINVAL;
>>              goto out_teardown;
>>          }
>> @@ -2681,16 +2691,15 @@ static int vfio_initfn(PCIDevice *pdev)
>>                          VFIO_REGION_TYPE_PCI_VENDOR_TYPE | 
>> PCI_VENDOR_ID_INTEL,
>>                          VFIO_REGION_SUBTYPE_INTEL_IGD_OPREGION, &opregion);
>>          if (ret) {
>> -            error_report("Device %s does not support requested IGD OpRegion 
>> "
>> -                         "feature", vdev->vbasedev.name);
>> +            error_setg_errno(&err, -ret,
>> +                             "does not support requested IGD OpRegion 
>> feature");
>>              goto out_teardown;
>>          }
>>  
>>          ret = vfio_pci_igd_opregion_init(vdev, opregion);
>>          g_free(opregion);
>>          if (ret) {
>> -            error_report("Device %s IGD OpRegion initialization failed",
>> -                         vdev->vbasedev.name);
>> +            error_setg_errno(&err, -ret, "IGD OpRegion initialization 
>> failed");
>>              goto out_teardown;
>>          }
>>      }
>> @@ -2726,6 +2735,10 @@ out_teardown:
>>      pci_device_set_intx_routing_notifier(&vdev->pdev, NULL);
>>      vfio_teardown_msi(vdev);
>>      vfio_bars_exit(vdev);
>> +error:
>> +    if (err) {
>> +        error_reportf_err(err, ERR_PREFIX, vdev->vbasedev.name);
>> +    }
>>      return ret;
>>  }
> 
> The value assigned to ret doesn't matter as long as it's negative, which
> makes me wonder why we bother with different values here.  Peeking
> ahead, I see you simplify this already as part of your conversion to
> realize().  Okay, that works for me.
At that stage it was a 1-1 conversion. Indeed this eventually disappears.

> 
>>  
>> diff --git a/include/hw/vfio/vfio-common.h b/include/hw/vfio/vfio-common.h
>> index 94dfae3..fd19880 100644
>> --- a/include/hw/vfio/vfio-common.h
>> +++ b/include/hw/vfio/vfio-common.h
>> @@ -30,6 +30,9 @@
>>  #include <linux/vfio.h>
>>  #endif
>>  
>> +#define ERR_PREFIX "vfio error: %s: "
>> +#define WARN_PREFIX "vfio warning: %s: "
>> +
>>  /*#define DEBUG_VFIO*/
>>  #ifdef DEBUG_VFIO
>>  #define DPRINTF(fmt, ...) \
> 
> We already discussed error message prefixes and errno strings.  I got my
> taste, you got yours.  Since this is your code, yours wins :)
> 

Here is a sample output. Using qmp interactively you easily get to know
which device BDF produced the error. Also qemu prints the -device option
which lead to the error.

(QEMU) device_add driver=vfio-pci host=0000:01:10.0 bus=head.2 addr=0x14
{"error": {"class": "GenericError", "desc": "vfio error: 0000:01:10.0:
error opening /dev/vfio/6: No such file or directory"}}

qemu-system-aarch64: -device vfio-pci,host=0000:01:10.0: vfio error:
0000:01:10.0: error opening /dev/vfio/6: No such file or directory

However in case of more complex usage (qmp scripts?), might be helpful
to get the BDF directly in the error output?

Thanks

Eric