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Date: Tue, 29 Nov 2011 12:56:03 +0000
Message-ID: <CAJSP0QVvmusMJMAaptg22TfYvu+6YMSdrH+yi_L012oUieeZ4w@mail.gmail.com>
From: Stefan Hajnoczi <stefanha@gmail.com>
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Subject: Re: [Qemu-devel] RFC: Design Doc for a new trace format (to support
 variable number/size of args per event) simpletrace-v2
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To: Markus Armbruster <armbru@redhat.com>
Cc: Harsh Bora <harsh@linux.vnet.ibm.com>, qemu-devel@nongnu.org, "Aneesh Kumar K. V" <aneesh.kumar@linux.vnet.ibm.com>

On Tue, Nov 29, 2011 at 12:35 PM, Markus Armbruster <armbru@redhat.com> wro=
te:
> Stefan Hajnoczi <stefanha@gmail.com> writes:
>
> [...]
>> So forget I said "self-describing" :). =A0I think the only changes from
>> the v1 format we need are:
>>
>> 1. New magic number to mark v2 format.
>>
>> 2. Trace records are no longer fixed-length, they include a size field:
>>
>> typedef struct {
>> =A0 =A0 uint32_t length; /* in bytes */
>> =A0 =A0 uint32_t reserved; /* unused */
>> =A0 =A0 uint64_t event;
>> =A0 =A0 uint64_t timestamp_ns;
>> =A0 =A0 uint8_t arguments[];
>> } TraceRecord;
>>
>> 3. Strings are serialized like this:
>>
>> uint16_t length;
>> char chars[length];
>
> 16 bit length? =A0Sure you want that?

You're right, it's more future-proof to use a larger type.  Since I
said uint32_t length in TraceRecord, uint32_t here would work well.

Stefan