Re: [PATCH 1 of 3] Remove use of bit fields in kvm trace structure

[Hollis Blanchard <hollisb@us.ibm.com>]

Slightly unconventional coding style, but Acked-by: Hollis Blanchard
<hollisb@us.ibm.com>

Eric, as I mentioned previously, bitfields cannot be used in portable
binary formats.

Avi, would you apply please?

-- 
Hollis Blanchard
IBM Linux Technology Center

On Thu, 2008-06-19 at 23:19 -0500, Jerone Young wrote:
> 2 files changed, 21 insertions(+), 11 deletions(-)
> include/linux/kvm.h  |   10 +++++++---
> virt/kvm/kvm_trace.c |   22 ++++++++++++++--------
> 
> 
> This patch fixes kvmtrace use on big endian systems. When using bit fields the compiler will lay data out in the wrong order expected when laid down into a file. This fixes it by using one variable instead of using bit fields.
> 
> Signed-off-by: Jerone Young <jyoung5@us.ibm.com>
> 
> diff --git a/include/linux/kvm.h b/include/linux/kvm.h
> --- a/include/linux/kvm.h
> +++ b/include/linux/kvm.h
> @@ -311,9 +311,13 @@ struct kvm_s390_interrupt {
> 
>  /* This structure represents a single trace buffer record. */
>  struct kvm_trace_rec {
> -	__u32 event:28;
> -	__u32 extra_u32:3;
> -	__u32 cycle_in:1;
> +	/* variable rec_val
> + 	 * is split into:
> + 	 * bits 0 - 27  -> event id
> + 	 * bits 28 -30  -> number of extra data args of size u32
> + 	 * bits 31      -> binary indicator for if tsc is in record
> + 	 */
> +	__u32 rec_val;
>  	__u32 pid;
>  	__u32 vcpu_id;
>  	union {
> diff --git a/virt/kvm/kvm_trace.c b/virt/kvm/kvm_trace.c
> --- a/virt/kvm/kvm_trace.c
> +++ b/virt/kvm/kvm_trace.c
> @@ -54,12 +54,15 @@ static void kvm_add_trace(void *probe_pr
>  	struct kvm_trace *kt = kvm_trace;
>  	struct kvm_trace_rec rec;
>  	struct kvm_vcpu *vcpu;
> -	int    i, extra, size;
> +	int    i, size;
> +	u32 extra;
> 
>  	if (unlikely(kt->trace_state != KVM_TRACE_STATE_RUNNING))
>  		return;
> +	
> +	/* set event id */	
> +	rec.rec_val	= 0x0fffffff & va_arg(*args, u32);
> 
> -	rec.event	= va_arg(*args, u32);
>  	vcpu		= va_arg(*args, struct kvm_vcpu *);
>  	rec.pid		= current->tgid;
>  	rec.vcpu_id	= vcpu->vcpu_id;
> @@ -67,21 +70,24 @@ static void kvm_add_trace(void *probe_pr
>  	extra   	= va_arg(*args, u32);
>  	WARN_ON(!(extra <= KVM_TRC_EXTRA_MAX));
>  	extra 		= min_t(u32, extra, KVM_TRC_EXTRA_MAX);
> -	rec.extra_u32   = extra;
> 
> -	rec.cycle_in 	= p->cycle_in;
> +	/* set inidicator for tcs record */
> +	rec.rec_val 	|= 0x80000000 & (p->cycle_in << 31);
> +	
> +	/* set extra data num */
> +	rec.rec_val     |= 0x70000000 & (extra << 28);
> 
> -	if (rec.cycle_in) {
> +	if (p->cycle_in) {
>  		rec.u.cycle.cycle_u64 = get_cycles();
> 
> -		for (i = 0; i < rec.extra_u32; i++)
> +		for (i = 0; i < extra; i++)
>  			rec.u.cycle.extra_u32[i] = va_arg(*args, u32);
>  	} else {
> -		for (i = 0; i < rec.extra_u32; i++)
> +		for (i = 0; i < extra; i++)
>  			rec.u.nocycle.extra_u32[i] = va_arg(*args, u32);
>  	}
> 
> -	size = calc_rec_size(rec.cycle_in, rec.extra_u32 * sizeof(u32));
> +	size = calc_rec_size(p->cycle_in, extra * sizeof(u32));
>  	relay_write(kt->rchan, &rec, size);
>  }
> 
> --
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