diff mbox series

[kvmtool,3/4] vfio: rework vfio_irq_set payload setting

Message ID 20190503171544.260901-4-andre.przywara@arm.com (mailing list archive)
State New, archived
Headers show
Series kvmtool: clang/GCC9 fixes | expand

Commit Message

Andre Przywara May 3, 2019, 5:15 p.m. UTC 
struct vfio_irq_set from the kernel headers contains a variable sized
array to hold a payload. The vfio_irq_eventfd struct puts the "fd"
member right after this, hoping it to automatically fit in the payload slot.
But having a variable sized type not at the end of a struct is a GNU C
extension, so clang will refuse to compile this.

Solve this by somewhat doing the compiler's job and place the payload
manually at the end of the structure.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
---
 vfio/pci.c | 21 +++++++++++++--------
 1 file changed, 13 insertions(+), 8 deletions(-)

Comments

Jean-Philippe Brucker May 29, 2019, 2:50 p.m. UTC | #1 
On 03/05/2019 18:15, Andre Przywara wrote:
> struct vfio_irq_set from the kernel headers contains a variable sized
> array to hold a payload. The vfio_irq_eventfd struct puts the "fd"
> member right after this, hoping it to automatically fit in the payload slot.
> But having a variable sized type not at the end of a struct is a GNU C
> extension, so clang will refuse to compile this.
> 
> Solve this by somewhat doing the compiler's job and place the payload
> manually at the end of the structure.
> 
> Signed-off-by: Andre Przywara <andre.przywara@arm.com>

It's odd that clang still warns about it even when passing -std=gnuXX.
The resulting code doesn't look particularly nice, but it would be good
to have the other patches upstream and this one is harmless, so:

Reviewed-by: Jean-Philippe Brucker <jean-philippe.brucker@arm.com>

> ---
>  vfio/pci.c | 21 +++++++++++++--------
>  1 file changed, 13 insertions(+), 8 deletions(-)
> 
> diff --git a/vfio/pci.c b/vfio/pci.c
> index a4086326..76e24c15 100644
> --- a/vfio/pci.c
> +++ b/vfio/pci.c
> @@ -9,11 +9,16 @@
>  #include <sys/time.h>
>  
>  /* Wrapper around UAPI vfio_irq_set */
> -struct vfio_irq_eventfd {
> +union vfio_irq_eventfd {
>  	struct vfio_irq_set	irq;
> -	int			fd;
> +	u8 buffer[sizeof(struct vfio_irq_set) + sizeof(int)];
>  };
>  
> +static void set_vfio_irq_eventd_payload(union vfio_irq_eventfd *evfd, int fd)
> +{
> +	memcpy(&evfd->irq.data, &fd, sizeof(fd));
> +}
> +
>  #define msi_is_enabled(state)		((state) & VFIO_PCI_MSI_STATE_ENABLED)
>  #define msi_is_masked(state)		((state) & VFIO_PCI_MSI_STATE_MASKED)
>  #define msi_is_empty(state)		((state) & VFIO_PCI_MSI_STATE_EMPTY)
> @@ -38,7 +43,7 @@ static int vfio_pci_enable_msis(struct kvm *kvm, struct vfio_device *vdev,
>  	int *eventfds;
>  	struct vfio_pci_device *pdev = &vdev->pci;
>  	struct vfio_pci_msi_common *msis = msix ? &pdev->msix : &pdev->msi;
> -	struct vfio_irq_eventfd single = {
> +	union vfio_irq_eventfd single = {
>  		.irq = {
>  			.argsz	= sizeof(single),
>  			.flags	= VFIO_IRQ_SET_DATA_EVENTFD |
> @@ -117,7 +122,7 @@ static int vfio_pci_enable_msis(struct kvm *kvm, struct vfio_device *vdev,
>  			continue;
>  
>  		single.irq.start = i;
> -		single.fd = fd;
> +		set_vfio_irq_eventd_payload(&single, fd);
>  
>  		ret = ioctl(vdev->fd, VFIO_DEVICE_SET_IRQS, &single);
>  		if (ret < 0) {
> @@ -1021,8 +1026,8 @@ static int vfio_pci_enable_intx(struct kvm *kvm, struct vfio_device *vdev)
>  {
>  	int ret;
>  	int trigger_fd, unmask_fd;
> -	struct vfio_irq_eventfd	trigger;
> -	struct vfio_irq_eventfd	unmask;
> +	union vfio_irq_eventfd	trigger;
> +	union vfio_irq_eventfd	unmask;
>  	struct vfio_pci_device *pdev = &vdev->pci;
>  	int gsi = pdev->intx_gsi;
>  
> @@ -1058,7 +1063,7 @@ static int vfio_pci_enable_intx(struct kvm *kvm, struct vfio_device *vdev)
>  		.start	= 0,
>  		.count	= 1,
>  	};
> -	trigger.fd = trigger_fd;
> +	set_vfio_irq_eventd_payload(&trigger, trigger_fd);
>  
>  	ret = ioctl(vdev->fd, VFIO_DEVICE_SET_IRQS, &trigger);
>  	if (ret < 0) {
> @@ -1073,7 +1078,7 @@ static int vfio_pci_enable_intx(struct kvm *kvm, struct vfio_device *vdev)
>  		.start	= 0,
>  		.count	= 1,
>  	};
> -	unmask.fd = unmask_fd;
> +	set_vfio_irq_eventd_payload(&unmask, unmask_fd);
>  
>  	ret = ioctl(vdev->fd, VFIO_DEVICE_SET_IRQS, &unmask);
>  	if (ret < 0) {
>
diff mbox series

Patch

diff --git a/vfio/pci.c b/vfio/pci.c
index a4086326..76e24c15 100644
--- a/vfio/pci.c
+++ b/vfio/pci.c
@@ -9,11 +9,16 @@ 
 #include <sys/time.h>
 
 /* Wrapper around UAPI vfio_irq_set */
-struct vfio_irq_eventfd {
+union vfio_irq_eventfd {
 	struct vfio_irq_set	irq;
-	int			fd;
+	u8 buffer[sizeof(struct vfio_irq_set) + sizeof(int)];
 };
 
+static void set_vfio_irq_eventd_payload(union vfio_irq_eventfd *evfd, int fd)
+{
+	memcpy(&evfd->irq.data, &fd, sizeof(fd));
+}
+
 #define msi_is_enabled(state)		((state) & VFIO_PCI_MSI_STATE_ENABLED)
 #define msi_is_masked(state)		((state) & VFIO_PCI_MSI_STATE_MASKED)
 #define msi_is_empty(state)		((state) & VFIO_PCI_MSI_STATE_EMPTY)
@@ -38,7 +43,7 @@  static int vfio_pci_enable_msis(struct kvm *kvm, struct vfio_device *vdev,
 	int *eventfds;
 	struct vfio_pci_device *pdev = &vdev->pci;
 	struct vfio_pci_msi_common *msis = msix ? &pdev->msix : &pdev->msi;
-	struct vfio_irq_eventfd single = {
+	union vfio_irq_eventfd single = {
 		.irq = {
 			.argsz	= sizeof(single),
 			.flags	= VFIO_IRQ_SET_DATA_EVENTFD |
@@ -117,7 +122,7 @@  static int vfio_pci_enable_msis(struct kvm *kvm, struct vfio_device *vdev,
 			continue;
 
 		single.irq.start = i;
-		single.fd = fd;
+		set_vfio_irq_eventd_payload(&single, fd);
 
 		ret = ioctl(vdev->fd, VFIO_DEVICE_SET_IRQS, &single);
 		if (ret < 0) {
@@ -1021,8 +1026,8 @@  static int vfio_pci_enable_intx(struct kvm *kvm, struct vfio_device *vdev)
 {
 	int ret;
 	int trigger_fd, unmask_fd;
-	struct vfio_irq_eventfd	trigger;
-	struct vfio_irq_eventfd	unmask;
+	union vfio_irq_eventfd	trigger;
+	union vfio_irq_eventfd	unmask;
 	struct vfio_pci_device *pdev = &vdev->pci;
 	int gsi = pdev->intx_gsi;
 
@@ -1058,7 +1063,7 @@  static int vfio_pci_enable_intx(struct kvm *kvm, struct vfio_device *vdev)
 		.start	= 0,
 		.count	= 1,
 	};
-	trigger.fd = trigger_fd;
+	set_vfio_irq_eventd_payload(&trigger, trigger_fd);
 
 	ret = ioctl(vdev->fd, VFIO_DEVICE_SET_IRQS, &trigger);
 	if (ret < 0) {
@@ -1073,7 +1078,7 @@  static int vfio_pci_enable_intx(struct kvm *kvm, struct vfio_device *vdev)
 		.start	= 0,
 		.count	= 1,
 	};
-	unmask.fd = unmask_fd;
+	set_vfio_irq_eventd_payload(&unmask, unmask_fd);
 
 	ret = ioctl(vdev->fd, VFIO_DEVICE_SET_IRQS, &unmask);
 	if (ret < 0) {