Re: [PATCH v3 3/3] vfio/pci: Continue to refactor vfio_pci_core_do_io_rw

Ramesh Thomas
2024-05-17T11:41:54Z

On 4/25/2024 9:56 AM, Gerd Bayer wrote:
> Convert if-elseif-chain into switch-case.
> Separate out and generalize the code from the if-clauses so the result
> can be used in the switch statement.
>
> Signed-off-by: Gerd Bayer <gbayer@linux.ibm.com>
> ---
> drivers/vfio/pci/vfio_pci_rdwr.c | 30 ++++++++++++++++++++++++------
> 1 file changed, 24 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/vfio/pci/vfio_pci_rdwr.c b/drivers/vfio/pci/vfio_pci_rdwr.c
> index 8ed06edaee23..634c00b03c71 100644
> --- a/drivers/vfio/pci/vfio_pci_rdwr.c
> +++ b/drivers/vfio/pci/vfio_pci_rdwr.c
> @@ -131,6 +131,20 @@ VFIO_IORDWR(32)
> VFIO_IORDWR(64)
> #endif
>
> +static int fill_size(size_t fillable, loff_t off)
> +{
> + unsigned int fill_size;
> +#if defined(ioread64) && defined(iowrite64)
> + for (fill_size = 8; fill_size >= 0; fill_size /= 2) {
> +#else
> + for (fill_size = 4; fill_size >= 0; fill_size /= 2) {

0 anyway reaches default case, so loop condition can be "fill_size > 0"
or at the start of function return 0 or -1 if fillable <= 0

> +#endif /* defined(ioread64) && defined(iowrite64) */
> + if (fillable >= fill_size && !(off % fill_size))
> + return fill_size;
> + }
> + return -1;
> +}
> +
> /*
> * Read or write from an __iomem region (MMIO or I/O port) with an excluded
> * range which is inaccessible. The excluded range drops writes and fills
> @@ -155,34 +169,38 @@ ssize_t vfio_pci_core_do_io_rw(struct vfio_pci_core_device *vdev, bool test_mem,
> else
> fillable = 0;
>
> + switch (fill_size(fillable, off)) {
> #if defined(ioread64) && defined(iowrite64)
> - if (fillable >= 8 && !(off % 8)) {
> + case 8:
> ret = vfio_pci_core_iordwr64(vdev, iswrite, test_mem,
> io, buf, off, &filled);
> if (ret)
> return ret;
This check and returning is common for all cases except default. Maybe
ret can be initialized to 0 before the switch block and do the check and
return after the switch block.

> + break;
>
> - } else
> #endif /* defined(ioread64) && defined(iowrite64) */
> - if (fillable >= 4 && !(off % 4)) {
> + case 4:
> ret = vfio_pci_core_iordwr32(vdev, iswrite, test_mem,
> io, buf, off, &filled);
> if (ret)
> return ret;
> + break;
>
> - } else if (fillable >= 2 && !(off % 2)) {
> + case 2:
> ret = vfio_pci_core_iordwr16(vdev, iswrite, test_mem,
> io, buf, off, &filled);
> if (ret)
> return ret;
> + break;
>
> - } else if (fillable) {
> + case 1:
> ret = vfio_pci_core_iordwr8(vdev, iswrite, test_mem,
> io, buf, off, &filled);
> if (ret)
> return ret;
> + break;
>
> - } else {
> + default:
> /* Fill reads with -1, drop writes */
> filled = min(count, (size_t)(x_end - off));
> if (!iswrite) {