Re: [PATCH v3 2/2] trace-cmd: Trace timesync to find pids that map vCPUs

[Tzvetomir Stoyanov <tz.stoyanov@gmail.com>]

On Fri, May 14, 2021 at 3:33 AM Steven Rostedt <rostedt@goodmis.org> wrote:
>
> From: "Steven Rostedt (VMware)" <rostedt@goodmis.org>
>
> If qemu is not found, then there's no mapping between the vCPUs of the
> guest and the threads that run them. As the time sync has the agent run on
> all the guest's CPUs, trace it, looking for all kvm_entry, which state
> which vCPU the host thread is entering on the guest, and then use that to
> create the mapping for the data files.
>
> Only parse for qemu if no CID is given on the command line.
>
> Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
> ---
> Changes since v1:
>  - Skipped v2 (added to v3 of this patch series)
>  - Used some of the new APIs of libtracefs 1.2
>  - Call read_qemu_guests is CID is not supplied on the command line.
>
>  tracecmd/include/trace-local.h |   2 +
>  tracecmd/trace-record.c        | 202 ++++++++++++++++++++++++++++++++-
>  2 files changed, 203 insertions(+), 1 deletion(-)
>
> diff --git a/tracecmd/include/trace-local.h b/tracecmd/include/trace-local.h
> index b3997d00..4c5669c9 100644
> --- a/tracecmd/include/trace-local.h
> +++ b/tracecmd/include/trace-local.h
> @@ -298,11 +298,13 @@ void update_first_instance(struct buffer_instance *instance, int topt);
>  void show_instance_file(struct buffer_instance *instance, const char *name);
>
>  struct trace_guest {
> +       struct tracefs_instance *instance;
>         char *name;
>         int cid;
>         int pid;
>         int cpu_max;
>         int *cpu_pid;
> +       int *task_pids;
>  };
>  struct trace_guest *trace_get_guest(unsigned int cid, const char *name);
>  bool trace_have_guests_pid(void);
> diff --git a/tracecmd/trace-record.c b/tracecmd/trace-record.c
> index 5dd8be4a..5219d60b 100644
> --- a/tracecmd/trace-record.c
> +++ b/tracecmd/trace-record.c
> @@ -3230,6 +3230,38 @@ static int do_accept(int sd)
>         return -1;
>  }
>
> +/* Find all the tasks associated with the guest pid */
> +static void find_tasks(struct trace_guest *guest)
> +{
> +       struct dirent *dent;
> +       char *path;
> +       DIR *dir;
> +       int ret;
> +       int tasks = 0;
> +
> +       ret = asprintf(&path, "/proc/%d/task", guest->pid);
> +       if (ret < 0)
> +               return;
> +
> +       dir = opendir(path);
> +       free(path);
> +       if (!dir)
> +               return;
> +
> +       while ((dent = readdir(dir))) {
> +               int *pids;
> +               if (!(dent->d_type == DT_DIR && is_digits(dent->d_name)))
> +                       continue;
> +               pids = realloc(guest->task_pids, sizeof(int) * (tasks + 2));
> +               if (!pids)
> +                       break;
> +               pids[tasks++] = strtol(dent->d_name, NULL, 0);
> +               pids[tasks] = -1;
> +               guest->task_pids = pids;
> +       }
> +       closedir(dir);
> +}
> +
>  static char *parse_guest_name(char *gname, int *cid, int *port)
>  {
>         struct trace_guest *guest;
> @@ -3250,10 +3282,18 @@ static char *parse_guest_name(char *gname, int *cid, int *port)
>         } else if (is_digits(gname))
>                 *cid = atoi(gname);
>
> -       read_qemu_guests();
> +       if (*cid < 0)
> +               read_qemu_guests();
> +
> +       if (*cid < 0)
> +               return NULL;

This check is not needed. If cid is not part of the string, let
read_qemu_guests() to try discover the VMs, instead of returning NULL.

[ ... ]


-- 
Tzvetomir (Ceco) Stoyanov
VMware Open Source Technology Center