[Libguestfs] [nbdkit PATCH 2/3] tests: Add coverage of zero in language bindings

[Eric Blake]

The existing test of language bindings was not covering any
use of NBD_CMD_WRITE_ZEROES, making it harder to test changes
to the plugin's zero callback.  Recent Linux kernels are now
smart enough to turn fallocate(2) with FALLOC_FL_ZERO_RANGE
into a SCSI WRITE SAME request, which qemu in turn converts
into an NBD_CMD_WRITE_ZEROES.  Since libguestfs does not
directly have an API for this, we have to use the backdoor
of guestfs_debug and fallocate(1).  But inspecting logs such
as tests/test-python.log, this change DOES prove that we
got a client request for write zeroes, and that the fallback
to pwrite due to test.py lacking a zero callback works.

Signed-off-by: Eric Blake <eblake at redhat.com>
---
 tests/test-lang-plugins.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/tests/test-lang-plugins.c b/tests/test-lang-plugins.c
index b695aaf..17e757b 100644
--- a/tests/test-lang-plugins.c
+++ b/tests/test-lang-plugins.c
@@ -122,6 +122,13 @@ main (int argc, char *argv[])
     exit (EXIT_FAILURE);
 #endif

+  /* Run fallocate(1) on the device to test zero path. */
+  if (guestfs_umount (g, "/") == 01)
+    exit (EXIT_FAILURE);
+  const char *cmd[] = { "fallocate", "-nzl", "64k", "/dev/sda", NULL };
+  char *s = guestfs_debug (g, "sh", (char **) cmd);
+  free (s);
+
   if (guestfs_shutdown (g) == -1)
     exit (EXIT_FAILURE);

-- 
2.14.3