return value for "if (!dev->is_physfn)"

Looking at drivers/pci/iov.c I see at least 3 different return values for if (!dev->is_physfn).

sriov_enable() and pci_enable_sriov()
[...]

	if (!dev->is_physfn)
		return -ENODEV;
pci_num_vf() and pci_vfs_assigned()
[...]
	if (!dev->is_physfn)
		return 0;
pci_sriov_set_totalvfs() and pci_sriov_get_totalvfs()
[...]
	if (!dev->is_physfn)
		return -EINVAL;

I'd like to make this consistently return one of the above. Question is, which one should it be? I'd lean towards -ENODEV, other opinions?

Stefan

Quoted 16 lines · Stefan Assmann

Looking at drivers/pci/iov.c I see at least 3 different return values for if (!dev->is_physfn).

sriov_enable() and pci_enable_sriov()
[...]

	if (!dev->is_physfn)
		return -ENODEV;
pci_num_vf() and pci_vfs_assigned()
[...]
	if (!dev->is_physfn)
		return 0;
pci_sriov_set_totalvfs() and pci_sriov_get_totalvfs()
[...]
	if (!dev->is_physfn)
		return -EINVAL;

Quoted 4 lines

I'd like to make this consistently return one of the above. Question is, which one should it be? I'd lean towards -ENODEV, other opinions?

Stefan

It all depends on how the results are meant to be interpreted.

In the case of pci_num_vf and pci_vfs_assigned the return of 0 is preferred since there are no VFs if the device is not a physical function. I really think pci_sriov_get_totalvfs should probably just return 0 as well since it is simply supposed to return the total number of VFs supported on the device and 0 would be valid in this case. Also that way the behavior is consistent if CONFIG_PCI_IOV is enabled or disabled in the kernel.

As for the rest my preference is ENOSYS rather than EINVAL or ENODEV. The issue is that the SR-IOV functionality is not implemented for the device or in the OS when we return the error so it would make sense to return that as an error code in these cases.

Thanks,

Alex

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Quoted 25 lines · Alexander Duyck

Quoted 16 lines · Stefan Assmann

Looking at drivers/pci/iov.c I see at least 3 different return values for if (!dev->is_physfn).

sriov_enable() and pci_enable_sriov()
[...]

    if (!dev->is_physfn)
        return -ENODEV;
pci_num_vf() and pci_vfs_assigned()
[...]
    if (!dev->is_physfn)
        return 0;
pci_sriov_set_totalvfs() and pci_sriov_get_totalvfs()
[...]
    if (!dev->is_physfn)
        return -EINVAL;

Quoted 5 lines

I'd like to make this consistently return one of the above. Question is,
which one should it be? I'd lean towards -ENODEV, other opinions?

Stefan

It all depends on how the results are meant to be interpreted.

Quoted 8 lines

In the case of pci_num_vf and pci_vfs_assigned the return of 0 is preferred since there are no VFs if the device is not a physical function. I really think pci_sriov_get_totalvfs should probably just return 0 as well since it is simply supposed to return the total number of VFs supported on the device and 0 would be valid in this case. Also that way the behavior is consistent if CONFIG_PCI_IOV is enabled or disabled in the kernel.

+1. returning enosys hangs the caller (echo/cat of sysfs) IIRC.

Quoted 9 lines

As for the rest my preference is ENOSYS rather than EINVAL or ENODEV. The issue is that the SR-IOV functionality is not implemented for the device or in the OS when we return the error so it would make sense to return that as an error code in these cases.

Thanks,

Alex

Quoted 34 lines · Don Dutile

Quoted 25 lines · Alexander Duyck

Quoted 16 lines · Stefan Assmann

Looking at drivers/pci/iov.c I see at least 3 different return values for if (!dev->is_physfn).

sriov_enable() and pci_enable_sriov()
[...]

     if (!dev->is_physfn)
         return -ENODEV;
pci_num_vf() and pci_vfs_assigned()
[...]
     if (!dev->is_physfn)
         return 0;
pci_sriov_set_totalvfs() and pci_sriov_get_totalvfs()
[...]
     if (!dev->is_physfn)
         return -EINVAL;

Quoted 5 lines

I'd like to make this consistently return one of the above. Question is,
which one should it be? I'd lean towards -ENODEV, other opinions?

Stefan

It all depends on how the results are meant to be interpreted.

Quoted 8 lines

In the case of pci_num_vf and pci_vfs_assigned the return of 0 is preferred since there are no VFs if the device is not a physical function. I really think pci_sriov_get_totalvfs should probably just return 0 as well since it is simply supposed to return the total number of VFs supported on the device and 0 would be valid in this case. Also that way the behavior is consistent if CONFIG_PCI_IOV is enabled or disabled in the kernel.

Quoted 11 lines

+1. returning enosys hangs the caller (echo/cat of sysfs) IIRC.

Quoted 9 lines

As for the rest my preference is ENOSYS rather than EINVAL or ENODEV. The issue is that the SR-IOV functionality is not implemented for the device or in the OS when we return the error so it would make sense to return that as an error code in these cases.

Thanks,

Alex

I am pretty sure it is safe to return ENOSYS since that is the return value used if you try to write to sriov_numvfs but do not have sriov_configure defined. That was one of the things that gave me the idea since it points to incomplete support for SR-IOV and returns a message along the lines of "echo: write error: Function not implemented" when trying to update those values.

Thanks,

Alex