[v3,19/40] ivshmem: Clean up MSI-X conditions

There are three predicates related to MSI-X:

* ivshmem_has_feature(s, IVSHMEM_MSI) is true unless the non-MSI-X
  variant of the device is selected with msi=off.

* msix_present() is true when the device has the PCI capability MSI-X.
  It's initially false, and becomes true during successful realize of
  the MSI-X variant of the device.  Thus, it's the same as
  ivshmem_has_feature(s, IVSHMEM_MSI) for realized devices.

* msix_enabled() is true when msix_present() is true and guest software
  has enabled MSI-X.

Code that differs between the non-MSI-X and the MSI-X variant of the
device needs to be guarded by ivshmem_has_feature(s, IVSHMEM_MSI) or
by msix_present(), except the latter works only for realized devices.

Code that depends on whether MSI-X is in use needs to be guarded with
msix_enabled().

Code review led me to two minor messes:

* ivshmem_vector_notify() calls msix_notify() even when
  !msix_enabled(), unlike most other MSI-X-capable devices.  As far as
  I can tell, msix_notify() does nothing when !msix_enabled().  Add
  the guard anyway.

* Most callers of ivshmem_use_msix() guard it with
  ivshmem_has_feature(s, IVSHMEM_MSI).  Not necessary, because
  ivshmem_use_msix() does nothing when !msix_present().  That's
  ivshmem's only use of msix_present(), though.  Guard it
  consistently, and drop the now redundant msix_present() check.
  While there, rename ivshmem_use_msix() to ivshmem_msix_vector_use().

Signed-off-by: Markus Armbruster <armbru@redhat.com>
---
 hw/misc/ivshmem.c | 22 ++++++++++------------
 1 file changed, 10 insertions(+), 12 deletions(-)

On Tue, Mar 15, 2016 at 7:34 PM, Markus Armbruster <armbru@redhat.com> wrote:
> There are three predicates related to MSI-X:
>
> * ivshmem_has_feature(s, IVSHMEM_MSI) is true unless the non-MSI-X
>   variant of the device is selected with msi=off.
>
> * msix_present() is true when the device has the PCI capability MSI-X.
>   It's initially false, and becomes true during successful realize of
>   the MSI-X variant of the device.  Thus, it's the same as
>   ivshmem_has_feature(s, IVSHMEM_MSI) for realized devices.
>
> * msix_enabled() is true when msix_present() is true and guest software
>   has enabled MSI-X.
>
> Code that differs between the non-MSI-X and the MSI-X variant of the
> device needs to be guarded by ivshmem_has_feature(s, IVSHMEM_MSI) or
> by msix_present(), except the latter works only for realized devices.
>
> Code that depends on whether MSI-X is in use needs to be guarded with
> msix_enabled().
>
> Code review led me to two minor messes:
>
> * ivshmem_vector_notify() calls msix_notify() even when
>   !msix_enabled(), unlike most other MSI-X-capable devices.  As far as
>   I can tell, msix_notify() does nothing when !msix_enabled().  Add
>   the guard anyway.
>
> * Most callers of ivshmem_use_msix() guard it with
>   ivshmem_has_feature(s, IVSHMEM_MSI).  Not necessary, because
>   ivshmem_use_msix() does nothing when !msix_present().  That's
>   ivshmem's only use of msix_present(), though.  Guard it
>   consistently, and drop the now redundant msix_present() check.
>   While there, rename ivshmem_use_msix() to ivshmem_msix_vector_use().
>
> Signed-off-by: Markus Armbruster <armbru@redhat.com>

Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>


> ---
>  hw/misc/ivshmem.c | 22 ++++++++++------------
>  1 file changed, 10 insertions(+), 12 deletions(-)
>
> diff --git a/hw/misc/ivshmem.c b/hw/misc/ivshmem.c
> index 1debce3..abcb1c1 100644
> --- a/hw/misc/ivshmem.c
> +++ b/hw/misc/ivshmem.c
> @@ -274,7 +274,9 @@ static void ivshmem_vector_notify(void *opaque)
>
>      IVSHMEM_DPRINTF("interrupt on vector %p %d\n", pdev, vector);
>      if (ivshmem_has_feature(s, IVSHMEM_MSI)) {
> -        msix_notify(pdev, vector);
> +        if (msix_enabled(pdev)) {
> +            msix_notify(pdev, vector);
> +        }
>      } else {
>          ivshmem_IntrStatus_write(s, 1);
>      }
> @@ -713,16 +715,11 @@ static void ivshmem_check_version(void *opaque, const uint8_t * buf, int size)
>  /* Select the MSI-X vectors used by device.
>   * ivshmem maps events to vectors statically, so
>   * we just enable all vectors on init and after reset. */
> -static void ivshmem_use_msix(IVShmemState * s)
> +static void ivshmem_msix_vector_use(IVShmemState *s)
>  {
>      PCIDevice *d = PCI_DEVICE(s);
>      int i;
>
> -    IVSHMEM_DPRINTF("%s, msix present: %d\n", __func__, msix_present(d));
> -    if (!msix_present(d)) {
> -        return;
> -    }
> -
>      for (i = 0; i < s->vectors; i++) {
>          msix_vector_use(d, i);
>      }
> @@ -734,7 +731,9 @@ static void ivshmem_reset(DeviceState *d)
>
>      s->intrstatus = 0;
>      s->intrmask = 0;
> -    ivshmem_use_msix(s);
> +    if (ivshmem_has_feature(s, IVSHMEM_MSI)) {
> +        ivshmem_msix_vector_use(s);
> +    }
>  }
>
>  static int ivshmem_setup_interrupts(IVShmemState *s)
> @@ -748,7 +747,7 @@ static int ivshmem_setup_interrupts(IVShmemState *s)
>          }
>
>          IVSHMEM_DPRINTF("msix initialized (%d vectors)\n", s->vectors);
> -        ivshmem_use_msix(s);
> +        ivshmem_msix_vector_use(s);
>      }
>
>      return 0;
> @@ -1040,9 +1039,8 @@ static int ivshmem_post_load(void *opaque, int version_id)
>      IVShmemState *s = opaque;
>
>      if (ivshmem_has_feature(s, IVSHMEM_MSI)) {
> -        ivshmem_use_msix(s);
> +        ivshmem_msix_vector_use(s);
>      }
> -
>      return 0;
>  }
>
> @@ -1070,7 +1068,7 @@ static int ivshmem_load_old(QEMUFile *f, void *opaque, int version_id)
>
>      if (ivshmem_has_feature(s, IVSHMEM_MSI)) {
>          msix_load(pdev, f);
> -        ivshmem_use_msix(s);
> +        ivshmem_msix_vector_use(s);
>      } else {
>          s->intrstatus = qemu_get_be32(f);
>          s->intrmask = qemu_get_be32(f);
> --
> 2.4.3
>
>