Re: [Qemu-devel] [PATCH 1/7] s390x/pci: factor out endianess conversion

[Cornelia Huck <cohuck@redhat.com>]

On Tue,  7 Nov 2017 18:24:33 +0100
Pierre Morel <pmorel@linux.vnet.ibm.com> wrote:

> There are two places where the same endianness conversion
> is done.
> Let's factor this out into a static function.
> 
> Signed-off-by: Pierre Morel <pmorel@linux.vnet.ibm.com>
> Reviewed-by: Yi Min Zhao <zyimin@linux.vnet.ibm.com>
> ---
>  hw/s390x/s390-pci-inst.c | 58 ++++++++++++++++++++++++++----------------------
>  1 file changed, 32 insertions(+), 26 deletions(-)
> 
> diff --git a/hw/s390x/s390-pci-inst.c b/hw/s390x/s390-pci-inst.c
> index 8e088f3..8fcb02d 100644
> --- a/hw/s390x/s390-pci-inst.c
> +++ b/hw/s390x/s390-pci-inst.c
> @@ -314,6 +314,35 @@ out:
>      return 0;
>  }
>  
> +/**
> + * This function swaps the data at ptr according from one
> + * endianness to the other.
> + * valid data in the uint64_t data field.

I'm not sure what that line is supposed to mean?

> + * @ptr: a pointer to a uint64_t data field
> + * @len: the length of the valid data, must be 1,2,4 or 8
> + */
> +static int zpci_endian_swap(uint64_t *ptr, uint8_t len)
> +{
> +    uint64_t data = *ptr;
> +    switch (len) {
> +    case 1:
> +        break;
> +    case 2:
> +        data = bswap16(data);
> +        break;
> +    case 4:
> +        data = bswap32(data);
> +        break;
> +    case 8:
> +        data = bswap64(data);
> +        break;
> +    default:
> +        return -EINVAL;
> +    }
> +    *ptr = data;
> +    return 0;
> +}
> +

I was expecting more code to use a similar pattern, but it seems
surprisingly uncommon.