Eric Blake writes:
> On 08/05/2016 10:59 AM, Lluís Vilanova wrote:
>> Signed-off-by: Lluís Vilanova <vilan...@ac.upc.edu>
>> ---
>> docs/hypertrace.txt | 141
>> +++++++++++++++++++++++++++++++++++++++++++++++++++
>> docs/tracing.txt | 3 +
>> 2 files changed, 144 insertions(+)
>> create mode 100644 docs/hypertrace.txt
>>
>> diff --git a/docs/hypertrace.txt b/docs/hypertrace.txt
>> new file mode 100644
>> index 0000000..4a31bcd
>> --- /dev/null
>> +++ b/docs/hypertrace.txt
>> @@ -0,0 +1,141 @@
>> += Hypertrace channel =
> No explicit copyright means that this document inherits the project
> default of GPLv2+. If that's not what you intended (or to be clear that
> it IS what you intended), you may want to add a copyright and license blurb.
Oh, I just followed what's on other docs. I can add a copyright notice on top.
>> +
>> +The hypertrace channel allows guest code to emit events in QEMU (the host)
>> using
>> +its tracing infrastructure (see "docs/trace.txt"). This works in both
>> 'system'
>> +and 'user' modes. That is, hypertrace is to tracing, what hypercalls are to
>> +system calls.
>> +
>> +You can use this to emit an event on both guest and QEMU (host) traces to
>> easily
>> +synchronize or correlate them. You could also modify you guest's tracing
>> system
>> +to emit all events through the hypertrace channel, providing a unified and
>> fully
>> +synchronized trace log. Another use case is timing the performance of guest
>> code
>> +when optimizing TCG (QEMU traces have a timestamp).
> Do you need to state that this channel should only be opened up to
> trusted guests, as otherwise it represents a security hole that a guest
> can cause a host denial of service by emitting events as fast as possible?
Mmmm, for user-mode ({linux,bsd}-user), that is not a problem, since there is a
single application running. In the softmmu case, it is already "protected" by
the OS filesystem permissions, which won't give you write access to a device by
default (unless you're root). I can certainly clarify that if that's what you
meant.
>> +3. Create a guest application using "qemu-hypertrace.h":
>> +
>> + cat > /tmp/my-hypertrace.c <<EOF
> I'd suggest <<\EOF here, to make it obvious that we don't want any $foo
> parameter expansion in the heredoc.
Got it.
>> + #include <stdio.h>
>> + #include <errno.h>
>> + #include <stdlib.h>
>> + #include <string.h>
>> + #include <qemu-hypertrace.h>
>> +
>> +
>> + int main(int argc, char **argv)
>> + {
>> + char *base = NULL;
>> + if (argc > 1) {
>> + base = argv[1];
>> + }
>> +
>> + /* In 'user' mode this path must be the same we will use to start
>> QEMU. */
>> + if (qemu_hypertrace_init(base) != 0) {
>> + fprintf(stderr, "error: qemu_hypertrace_init: %s\n",
>> strerror(errno));
> Worth using perror() in this example code?
Yes, thanks.
> Overall looks reasonable.
Thanks,
Lluis
