static ssize_t vfio_config_do_rw()

in pci/vfio_pci_config.c [1805:1886]

• 62 lines of code
• 19 McCabe index (conditional complexity)

static ssize_t vfio_config_do_rw(struct vfio_pci_core_device *vdev, char __user *buf,
				 size_t count, loff_t *ppos, bool iswrite)
{
	struct pci_dev *pdev = vdev->pdev;
	struct perm_bits *perm;
	__le32 val = 0;
	int cap_start = 0, offset;
	u8 cap_id;
	ssize_t ret;

	if (*ppos < 0 || *ppos >= pdev->cfg_size ||
	    *ppos + count > pdev->cfg_size)
		return -EFAULT;

	/*
	 * Chop accesses into aligned chunks containing no more than a
	 * single capability.  Caller increments to the next chunk.
	 */
	count = min(count, vfio_pci_cap_remaining_dword(vdev, *ppos));
	if (count >= 4 && !(*ppos % 4))
		count = 4;
	else if (count >= 2 && !(*ppos % 2))
		count = 2;
	else
		count = 1;

	ret = count;

	cap_id = vdev->pci_config_map[*ppos];

	if (cap_id == PCI_CAP_ID_INVALID) {
		perm = &unassigned_perms;
		cap_start = *ppos;
	} else if (cap_id == PCI_CAP_ID_INVALID_VIRT) {
		perm = &virt_perms;
		cap_start = *ppos;
	} else {
		if (*ppos >= PCI_CFG_SPACE_SIZE) {
			WARN_ON(cap_id > PCI_EXT_CAP_ID_MAX);

			perm = &ecap_perms[cap_id];
			cap_start = vfio_find_cap_start(vdev, *ppos);
		} else {
			WARN_ON(cap_id > PCI_CAP_ID_MAX);

			perm = &cap_perms[cap_id];

			if (cap_id == PCI_CAP_ID_MSI)
				perm = vdev->msi_perm;

			if (cap_id > PCI_CAP_ID_BASIC)
				cap_start = vfio_find_cap_start(vdev, *ppos);
		}
	}

	WARN_ON(!cap_start && cap_id != PCI_CAP_ID_BASIC);
	WARN_ON(cap_start > *ppos);

	offset = *ppos - cap_start;

	if (iswrite) {
		if (!perm->writefn)
			return ret;

		if (copy_from_user(&val, buf, count))
			return -EFAULT;

		ret = perm->writefn(vdev, *ppos, count, perm, offset, val);
	} else {
		if (perm->readfn) {
			ret = perm->readfn(vdev, *ppos, count,
					   perm, offset, &val);
			if (ret < 0)
				return ret;
		}

		if (copy_to_user(buf, &val, count))
			return -EFAULT;
	}

	return ret;
}