Re: [Xen-devel] [PATCH] xen/vm_event: fix rc check for uninitialized ring

[Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>]

On 5/24/19 4:15 PM, Juergen Gross wrote:
> vm_event_claim_slot() returns -EOPNOTSUPP for an uninitialized ring
> since commit 15e4dd5e866b43bbc ("common/vm_event: Initialize vm_event
> lists on domain creation"), but the callers test for -ENOSYS.
>
> Correct the callers.
>
> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
> ---
>   xen/arch/x86/mm/p2m.c | 2 +-
>   xen/common/monitor.c  | 2 +-
>   xen/common/vm_event.c | 2 +-
>   3 files changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/xen/arch/x86/mm/p2m.c b/xen/arch/x86/mm/p2m.c
> index 57c5eeda91..8a9a1153a8 100644
> --- a/xen/arch/x86/mm/p2m.c
> +++ b/xen/arch/x86/mm/p2m.c
> @@ -1705,7 +1705,7 @@ void p2m_mem_paging_populate(struct domain *d, unsigned 
> long gfn_l)
>   
>       /* We're paging. There should be a ring */
>       int rc = vm_event_claim_slot(d, d->vm_event_paging);
> -    if ( rc == -ENOSYS )
> +    if ( rc == -EOPNOTSUPP )
>       {
>           gdprintk(XENLOG_ERR, "Domain %hu paging gfn %lx yet no ring "
>                                "in place\n", d->domain_id, gfn_l);
> diff --git a/xen/common/monitor.c b/xen/common/monitor.c
> index cb5f37fdb2..d5c9ff1cbf 100644
> --- a/xen/common/monitor.c
> +++ b/xen/common/monitor.c
> @@ -98,7 +98,7 @@ int monitor_traps(struct vcpu *v, bool sync, 
> vm_event_request_t *req)
>       {
>       case 0:
>           break;
> -    case -ENOSYS:
> +    case -EOPNOTSUPP:
>           /*
>            * If there was no ring to handle the event, then
>            * simply continue executing normally.
> diff --git a/xen/common/vm_event.c b/xen/common/vm_event.c
> index 6e68be47bc..7b4ebced16 100644
> --- a/xen/common/vm_event.c
> +++ b/xen/common/vm_event.c
> @@ -513,7 +513,7 @@ bool vm_event_check_ring(struct vm_event_domain *ved)
>    * this function will always return 0 for a guest.  For a non-guest, we check
>    * for space and return -EBUSY if the ring is not available.
>    *
> - * Return codes: -ENOSYS: the ring is not yet configured
> + * Return codes: -EOPNOTSUPP: the ring is not yet configured
>    *               -EBUSY: the ring is busy
>    *               0: a spot has been reserved
>    *
But vm_event_grab_slot() (which ends up being what vm_event_wait_slot() 
returns), still returns -ENOSYS:
463 static int vm_event_grab_slot(struct vm_event_domain *ved, int foreign)
464 {
465     unsigned int avail_req;
466
467     if ( !ved->ring_page )
468         return -ENOSYS;

Although we can't get to that part if vm_event_check_ring() returns 
false, we should probably return -EOPNOTSUPP from there as well. In 
fact, I wonder if any of the -ENOSYS returns in vm_event.c should not be 
replaced with return -EOPNOTSUPPs.
Anyway, the change does clearly improve the code even without settling 
the above questions, so:
Acked-by: Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>


Thanks,
Razvan

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