Re: [PATCH v2] plugins/syscall: Added a table-like summary output

["Alex Bennée" <alex.bennee@linaro.org>]

Mahmoud Mandour <ma.mandourr@gmail.com> writes:

> Added a table-like output which contains the total number of calls
> for each used syscall along with the number of errors that occurred.
>
> Per-call tracing is still available through supplying the argument
> ``print`` to the plugin.
>
> Signed-off-by: Mahmoud Mandour <ma.mandourr@gmail.com>
> ---
> v1: https://lists.gnu.org/archive/html/qemu-devel/2021-04/msg02623.html
> v1 -> v2: Removed debugging code in the on-return from syscall callback 
>           that was silently existent.
>
>  tests/plugin/syscall.c | 91 +++++++++++++++++++++++++++++++++++++++---
>  1 file changed, 85 insertions(+), 6 deletions(-)
>
> diff --git a/tests/plugin/syscall.c b/tests/plugin/syscall.c
> index 53ee2ab6c4..b66a930635 100644
> --- a/tests/plugin/syscall.c
> +++ b/tests/plugin/syscall.c
> @@ -16,32 +16,111 @@
>  
>  QEMU_PLUGIN_EXPORT int qemu_plugin_version = QEMU_PLUGIN_VERSION;
>  
> +typedef struct {
> +    int64_t calls;
> +    int64_t errors;
> +} SyscallStats;
> +
> +static GHashTable *syscalls_statistics;
> +
> +static bool percall_print;
> +
>  static void vcpu_syscall(qemu_plugin_id_t id, unsigned int vcpu_index,
>                           int64_t num, uint64_t a1, uint64_t a2,
>                           uint64_t a3, uint64_t a4, uint64_t a5,
>                           uint64_t a6, uint64_t a7, uint64_t a8)
>  {
> -    g_autofree gchar *out = g_strdup_printf("syscall #%" PRIi64 "\n", num);
> -    qemu_plugin_outs(out);
> +    if (!percall_print) {

I think you could eliminate the percall_print global and just invert the
test and have if (syscall_statisitics)

> +        SyscallStats *syscall_entry;
> +
> +        syscall_entry =
> +            (SyscallStats *) g_hash_table_lookup(syscalls_statistics,
> +                                                  GINT_TO_POINTER(num));
> +
> +        if (!syscall_entry) {
> +            syscall_entry = g_new(SyscallStats, 1);
> +            syscall_entry->calls = 1;
> +            syscall_entry->errors = 0;
> +
> +            g_hash_table_insert(syscalls_statistics, GINT_TO_POINTER(num),
> +                                (gpointer) syscall_entry);

You you wrap up the entry creation into a helper it would make the code
less cluttered here, e.g.:

     syscall_entry = get_or_create_entry();
     syscall_entry->calls++;

> +        } else {
> +            syscall_entry->calls++;
> +        }
> +    } else {
> +        g_autofree gchar *out = g_strdup_printf("syscall #%" PRIi64 "\n", num);
> +        qemu_plugin_outs(out);
> +    }
>  }
>  
>  static void vcpu_syscall_ret(qemu_plugin_id_t id, unsigned int vcpu_idx,
>                               int64_t num, int64_t ret)
> +{
> +    if (!percall_print) {
> +        SyscallStats *syscall_entry;
> +
> +        syscall_entry =
> +            (SyscallStats *) g_hash_table_lookup(syscalls_statistics,
> +                                                  GINT_TO_POINTER(num));
> +        if (ret < 0) {
> +            syscall_entry->errors++;
> +        }
> +    } else {
> +        g_autofree gchar *out;
> +        out = g_strdup_printf("syscall #%" PRIi64 " returned -> %" PRIi64 "\n",
> +                num, ret);
> +        qemu_plugin_outs(out);
> +    }

ditto.

> +}
> +
> +/* ************************************************************************* */
> +
> +void print_entry(gpointer key, gpointer val, gpointer user_data)
>  {
>      g_autofree gchar *out;
> -    out = g_strdup_printf("syscall #%" PRIi64 " returned -> %" PRIi64 "\n",
> -            num, ret);
> +    int64_t syscall_num = (int64_t) key;
> +    SyscallStats *syscall_entry = (SyscallStats *) val;
> +    out = g_strdup_printf(
> +        "%-13" PRIi64 "%-6" PRIi64 " %" PRIi64 "\n",
> +        syscall_num, syscall_entry->calls, syscall_entry->errors);
>      qemu_plugin_outs(out);
>  }
>  
> -/* ************************************************************************* */
> +static void plugin_exit(qemu_plugin_id_t id, void *p)
> +{
> +    if (!percall_print) {
> +        qemu_plugin_outs("syscall no.  calls  errors\n");
> +        g_hash_table_foreach(syscalls_statistics, &print_entry,
> NULL);

Sorting the hash list by calls would be a nice improvement - see howvec
for an example of how to use g_hash_table_get_values/g_list_sort.

For cleanliness you should also clean-up the syscall_statisitics hash
table and deallocation although in practice it doesn't really matter as
use space is about to exit anyway.

> +    }
> +}
>  
> -static void plugin_exit(qemu_plugin_id_t id, void *p) {}
> +void free_entry(gpointer entry)
> +{
> +    g_free(entry);
> +}
>  
>  QEMU_PLUGIN_EXPORT int qemu_plugin_install(qemu_plugin_id_t id,
>                                             const qemu_info_t *info,
>                                             int argc, char **argv)
>  {
> +    int i;
> +
> +    for (i = 0; i < argc; i++) {
> +        char *opt = argv[i];
> +        if (g_strcmp0(opt, "print") == 0) {
> +            percall_print = true;

So this would be a local now and or even:

  if (argc == 0) {
      syscalls_statistics = g_hash_table_new_full(g_direct_hash, g_direct_equal,  NULL, &free_entry);
  } else {
      for (i = 0; i < argc; i++) {
          ...

> +        } else {
> +            fprintf(stderr, "unsupported argument: %s\n", opt);
> +            return -1;
> +        }
> +    }
> +
> +    if (!percall_print) {
> +        syscalls_statistics =
> +            g_hash_table_new_full(g_direct_hash, g_direct_equal,
> +                    NULL, &free_entry);

For a simple non-nested structure you might even get away with a plain g_hash_table_new()

> +    }
> +
>      qemu_plugin_register_vcpu_syscall_cb(id, vcpu_syscall);
>      qemu_plugin_register_vcpu_syscall_ret_cb(id, vcpu_syscall_ret);
>      qemu_plugin_register_atexit_cb(id, plugin_exit, NULL);


-- 
Alex Bennée