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

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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@xxxxxxxxxxxxx>
---
  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) {





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