Re: [PATCH v19 03/15] trace-cmd: Find and store pids of tasks, which run virtual CPUs of given VM

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

On Thu, Feb 27, 2020 at 6:13 AM Steven Rostedt <rostedt@goodmis.org> wrote:
>
> On Fri, 31 Jan 2020 14:10:59 +0200
> "Tzvetomir Stoyanov (VMware)" <tz.stoyanov@gmail.com> wrote:
>
> > From: Tzvetomir Stoyanov <tstoyanov@vmware.com>
> >
> > In order to match host and guest events, a mapping between guest VCPU
> > and the host task, running this VCPU is needed. Extended existing
> > struct guest to hold such mapping and added logic in read_qemu_guests()
> > function to initialize it. Implemented a new internal API,
> > get_guest_vcpu_pid(), to retrieve VCPU-task mapping for given VM.
> >
> > Signed-off-by: Tzvetomir Stoyanov <tstoyanov@vmware.com>
> > ---
> >  tracecmd/include/trace-local.h |  2 ++
> >  tracecmd/trace-record.c        | 54 ++++++++++++++++++++++++++++++++++
> >  2 files changed, 56 insertions(+)
> >
> > diff --git a/tracecmd/include/trace-local.h b/tracecmd/include/trace-local.h
> > index 29f2779..a5cf064 100644
> > --- a/tracecmd/include/trace-local.h
> > +++ b/tracecmd/include/trace-local.h
> > @@ -247,6 +247,8 @@ void update_first_instance(struct buffer_instance *instance, int topt);
> >
> >  void show_instance_file(struct buffer_instance *instance, const char *name);
> >
> > +int get_guest_vcpu_pid(unsigned int guest_cid, unsigned int guest_vcpu);
> > +
> >  /* moved from trace-cmd.h */
> >  void tracecmd_create_top_instance(char *name);
> >  void tracecmd_remove_instances(void);
> > diff --git a/tracecmd/trace-record.c b/tracecmd/trace-record.c
> > index 28fe31b..b479e91 100644
> > --- a/tracecmd/trace-record.c
> > +++ b/tracecmd/trace-record.c
> > @@ -3031,10 +3031,12 @@ static bool is_digits(const char *s)
> >       return true;
> >  }
> >
> > +#define VCPUS_MAX 256
> >  struct guest {
> >       char *name;
> >       int cid;
> >       int pid;
> > +     int cpu_pid[VCPUS_MAX];
>
> Although this is probably fine for the near future, I don't like
> arbitrary limits that don't have to do with max sizes of the storage
> unit (like max int).
>
> Why is the cpu_pid a static array and not one that is allocated? We
> could use realloc, couldn't we, in the loading of it?
>

I did it to simplify the PoC implementation and never changed it to be
a dynamic array,
I'll reimplement it now.
Thanks Steven!

> -- Steve
>
> >  };
> >
> >  static struct guest *guests;
> > @@ -3052,6 +3054,43 @@ static char *get_qemu_guest_name(char *arg)
> >       return arg;
> >  }
> >
> > +static void read_qemu_guests_pids(char *guest_task, struct guest *guest)
> > +{
> > +     struct dirent *entry;
> > +     char path[PATH_MAX];
> > +     char *buf = NULL;
> > +     size_t n = 0;
> > +     int vcpu;
> > +     DIR *dir;
> > +     FILE *f;
> > +
> > +     snprintf(path, sizeof(path), "/proc/%s/task", guest_task);
> > +     dir = opendir(path);
> > +     if (!dir)
> > +             return;
> > +
> > +     while ((entry = readdir(dir))) {
> > +             if (!(entry->d_type == DT_DIR && is_digits(entry->d_name)))
> > +                     continue;
> > +
> > +             snprintf(path, sizeof(path), "/proc/%s/task/%s/comm",
> > +                      guest_task, entry->d_name);
> > +             f = fopen(path, "r");
> > +             if (!f)
> > +                     continue;
> > +
> > +             if (getline(&buf, &n, f) >= 0 &&
> > +                 strncmp(buf, "CPU ", 4) == 0) {
> > +                     vcpu = atoi(buf + 4);
> > +                     if (vcpu >= 0 && vcpu < VCPUS_MAX)
> > +                             guest->cpu_pid[vcpu] = atoi(entry->d_name);
> > +             }
> > +
> > +             fclose(f);
> > +     }
> > +     free(buf);
> > +}
> > +
> >  static void read_qemu_guests(void)
> >  {
> >       static bool initialized;
> > @@ -3115,6 +3154,8 @@ static void read_qemu_guests(void)
> >               if (!is_qemu)
> >                       goto next;
> >
> > +             read_qemu_guests_pids(entry->d_name, &guest);
> > +
> >               guests = realloc(guests, (guests_len + 1) * sizeof(*guests));
> >               if (!guests)
> >                       die("Can not allocate guest buffer");
> > @@ -3160,6 +3201,19 @@ static char *parse_guest_name(char *guest, int *cid, int *port)
> >       return guest;
> >  }
> >
> > +int get_guest_vcpu_pid(unsigned int guest_cid, unsigned int guest_vcpu)
> > +{
> > +     int i;
> > +
> > +     if (!guests || guest_vcpu >= VCPUS_MAX)
> > +             return -1;
> > +
> > +     for (i = 0; i < guests_len; i++)
> > +             if (guest_cid == guests[i].cid)
> > +                     return guests[i].cpu_pid[guest_vcpu];
> > +     return -1;
> > +}
> > +
> >  static void set_prio(int prio)
> >  {
> >       struct sched_param sp;
>


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