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Re: [Qemu-devel] [PATCH 1/6] hypertrace: Add documentation
From: |
Eric Blake |
Subject: |
Re: [Qemu-devel] [PATCH 1/6] hypertrace: Add documentation |
Date: |
Fri, 5 Aug 2016 11:17:17 -0600 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.3.0 |
On 08/05/2016 10:59 AM, Lluís Vilanova wrote:
> Signed-off-by: Lluís Vilanova <address@hidden>
> ---
> 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.
> +
> +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?
> +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.
> + #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?
Overall looks reasonable.
--
Eric Blake eblake redhat com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
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