[Libguestfs] [PATCH nbdkit v2 3/3] filters: stats: Add flush stats

[Nir Soffer]

flush is usually called once but it can take significant time, so we
need to include it.

Here is an example run with this change:

$ ./nbdkit --foreground \
    --unix /tmp/nbd.sock \
    --exportname '' \
    --filter stats \
    file file=/var/tmp/dst.img \
    statsfile=/dev/stderr \
    --run 'qemu-img convert -p -n -f raw -O raw -T none /var/tmp/fedora-30.img nbd:unix:/tmp/nbd.sock'
    (100.00/100%)
total: 2299 ops, 2.172 s, 6442450944 bytes, 6.000 GiB, 2829.295 MiB/s
write: 1271 ops, 0.356 s, 1219244032 bytes, 1.136 GiB, 3269.711 MiB/s
zero: 1027 ops, 0.012 s, 5223206912 bytes, 4.864 GiB, 431052.118 MiB/s
extents: 1 ops, 0.000 s, 2147483136 bytes, 2.000 GiB, 107789447.985 MiB/s
flush: 2 ops, 1.156 s
---
 filters/stats/stats.c | 36 ++++++++++++++++++++++++++++++------
 1 file changed, 30 insertions(+), 6 deletions(-)

diff --git a/filters/stats/stats.c b/filters/stats/stats.c
index 2c92c65..1d0f242 100644
--- a/filters/stats/stats.c
+++ b/filters/stats/stats.c
@@ -73,6 +73,7 @@ static stat trim_st    = { "trim" };
 static stat zero_st    = { "zero" };
 static stat extents_st = { "extents" };
 static stat cache_st   = { "cache" };
+static stat flush_st   = { "flush" };
 
 static inline double
 calc_rate (uint64_t bytes, int64_t usecs)
@@ -83,14 +84,20 @@ calc_rate (uint64_t bytes, int64_t usecs)
 static inline void
 print_stat (const stat *st)
 {
-  if (st->ops > 0)
-    fprintf (fp, "%s: %" PRIu64 " ops, %.3f s, %" PRIu64 " bytes, %.3f GiB, %.3f MiB/s\n",
+  if (st->ops > 0) {
+    fprintf (fp, "%s: %" PRIu64 " ops, %.3f s",
              st->name,
              st->ops,
-             st->usecs / USEC,
-             st->bytes,
-             st->bytes / GiB,
-             calc_rate (st->bytes, st->usecs));
+             st->usecs / USEC);
+
+    if (st->bytes > 0)
+      fprintf (fp, ", %" PRIu64 " bytes, %.3f GiB, %.3f MiB/s",
+               st->bytes,
+               st->bytes / GiB,
+               calc_rate (st->bytes, st->usecs));
+
+    fprintf (fp, "\n");
+  }
 }
 
 static inline void
@@ -117,6 +124,7 @@ print_stats (int64_t usecs)
   print_stat (&zero_st);
   print_stat (&extents_st);
   print_stat (&cache_st);
+  print_stat (&flush_st);
 
   fflush (fp);
 }
@@ -263,6 +271,21 @@ stats_trim (struct nbdkit_next_ops *next_ops, void *nxdata,
   return r;
 }
 
+/* Flush. */
+static int
+stats_flush (struct nbdkit_next_ops *next_ops, void *nxdata,
+             void *handle, uint32_t flags,
+             int *err)
+{
+  struct timeval start;
+  int r;
+
+  gettimeofday (&start, NULL);
+  r = next_ops->flush (nxdata, flags, err);
+  if (r == 0) record_stat (&flush_st, 0, &start);
+  return r;
+}
+
 /* Zero. */
 static int
 stats_zero (struct nbdkit_next_ops *next_ops, void *nxdata,
@@ -325,6 +348,7 @@ static struct nbdkit_filter filter = {
   .pread             = stats_pread,
   .pwrite            = stats_pwrite,
   .trim              = stats_trim,
+  .flush             = stats_flush,
   .zero              = stats_zero,
   .extents           = stats_extents,
   .cache             = stats_cache,
-- 
2.21.0