[Libguestfs] [PATCH nbdkit 2/4] fua: Add fuamode=pass.

[Richard W.M. Jones]

Passes FUA and flush requests unchanged.  A convenient way to turn the
filter into a no-op without rewriting the whole nbdkit command line.
---
 filters/fua/nbdkit-fua-filter.pod |  5 +++++
 filters/fua/fua.c                 | 12 +++++++++++-
 tests/test-fua.sh                 | 21 ++++++++++++++++++---
 3 files changed, 34 insertions(+), 4 deletions(-)

diff --git a/filters/fua/nbdkit-fua-filter.pod b/filters/fua/nbdkit-fua-filter.pod
index 6e8f87e2..3d20b56a 100644
--- a/filters/fua/nbdkit-fua-filter.pod
+++ b/filters/fua/nbdkit-fua-filter.pod
@@ -48,6 +48,11 @@ client did not request it.  In turn client flush requests become
 no-ops.  It refuses to load if the plugin's C<.can_fua> callback
 returns C<NBDKIT_FUA_NONE>.
 
+=item B<fuamode=pass>
+
+Pass through FUA and flush requests unchanged.  Turns the filter into
+a no-op.
+
 =back
 
 =head1 EXAMPLES
diff --git a/filters/fua/fua.c b/filters/fua/fua.c
index cee05eed..6bc62a02 100644
--- a/filters/fua/fua.c
+++ b/filters/fua/fua.c
@@ -46,6 +46,7 @@ static enum FuaMode {
   EMULATE,
   NATIVE,
   FORCE,
+  PASS,
 } fuamode;
 
 static int
@@ -61,6 +62,8 @@ fua_config (nbdkit_next_config *next, void *nxdata,
       fuamode = NATIVE;
     else if (strcmp (value, "force") == 0)
       fuamode = FORCE;
+    else if (strcmp (value, "pass") == 0)
+      fuamode = PASS;
     else {
       nbdkit_error ("unknown fuamode '%s'", value);
       return -1;
@@ -71,7 +74,8 @@ fua_config (nbdkit_next_config *next, void *nxdata,
 }
 
 #define fua_config_help \
-  "fuamode=<MODE>       One of 'none' (default), 'emulate', 'native', 'force'.\n" \
+  "fuamode=<MODE>       One of 'none' (default), 'emulate', 'native',\n" \
+  "                       'force', 'pass'."
 
 /* Check that desired mode is supported by plugin. */
 static int
@@ -86,6 +90,7 @@ fua_prepare (struct nbdkit_next_ops *next_ops, void *nxdata, void *handle,
 
   switch (fuamode) {
   case NONE:
+  case PASS:
     break;
   case EMULATE:
     r = next_ops->can_flush (nxdata);
@@ -132,6 +137,8 @@ fua_can_fua (struct nbdkit_next_ops *next_ops, void *nxdata, void *handle)
   case NATIVE:
   case FORCE:
     return NBDKIT_FUA_NATIVE;
+  case PASS:
+    return next_ops->can_fua (nxdata);
   }
   abort ();
 }
@@ -155,6 +162,7 @@ fua_pwrite (struct nbdkit_next_ops *next_ops, void *nxdata,
     }
     break;
   case NATIVE:
+  case PASS:
     break;
   case FORCE:
     flags |= NBDKIT_FLAG_FUA;
@@ -194,6 +202,7 @@ fua_trim (struct nbdkit_next_ops *next_ops, void *nxdata,
     }
     break;
   case NATIVE:
+  case PASS:
     break;
   case FORCE:
     flags |= NBDKIT_FLAG_FUA;
@@ -224,6 +233,7 @@ fua_zero (struct nbdkit_next_ops *next_ops, void *nxdata,
     }
     break;
   case NATIVE:
+  case PASS:
     break;
   case FORCE:
     flags |= NBDKIT_FLAG_FUA;
diff --git a/tests/test-fua.sh b/tests/test-fua.sh
index 1c869e96..5fb5e929 100755
--- a/tests/test-fua.sh
+++ b/tests/test-fua.sh
@@ -39,7 +39,8 @@ files="fua.img
        fua1.log fua1.pid
        fua2.log fua2.pid
        fua3.log fua3.pid
-       fua4.log fua4.pid"
+       fua4.log fua4.pid
+       fua5.log fua5.pid"
 rm -f $files
 
 # Prep images, and check that qemu-io understands the actions we plan on
@@ -63,16 +64,19 @@ cleanup ()
     cat fua3.log || :
     echo "Log 4 file contents:"
     cat fua4.log || :
+    echo "Log 5 file contents:"
+    cat fua5.log || :
     rm -f $files
     rm -rf $sockdir
 }
 cleanup_fn cleanup
 
-# Run four parallel nbdkit; to compare the logs and see what changes.
+# Run parallel nbdkit; to compare the logs and see what changes.
 # 1: fuamode=none (default): client should send flush instead
 # 2: fuamode=emulate: log shows that blocksize optimizes fua to flush
 # 3: fuamode=native: log shows that blocksize preserves fua
 # 4: fuamode=force: log shows that fua is always enabled
+# 5: fuamode=pass: fua flag and flush unchanged
 start_nbdkit -P fua1.pid -U $sockdir/fua1.sock \
              --filter=log --filter=fua \
              file logfile=fua1.log fua.img
@@ -85,10 +89,13 @@ start_nbdkit -P fua3.pid -U $sockdir/fua3.sock \
 start_nbdkit -P fua4.pid -U $sockdir/fua4.sock \
              --filter=fua --filter=log \
              file logfile=fua4.log fua.img fuamode=force
+start_nbdkit -P fua5.pid -U $sockdir/fua5.sock \
+             --filter=fua --filter=log \
+             file logfile=fua5.log fua.img fuamode=pass
 
 # Perform a flush, write, and zero, first without then with FUA
 for f in '' -f; do
-    for i in {1..4}; do
+    for i in {1..5}; do
 	qemu-io -f raw -t none -c flush -c "w $f 0 64k" -c "w -z $f 64k 64k" \
 		 "nbd+unix://?socket=$sockdir/fua$i.sock"
     done
@@ -124,3 +131,11 @@ if grep 'Flush' fua4.log; then
     echo "filter should have elided flush"
     exit 1
 fi
+
+# Test 5: Flush should be passed through.
+# There should also be one set of fua=0 and a second set of fua=1.
+grep 'Flush' fua5.log
+grep 'connection=1 Write.*fua=0' fua5.log
+grep 'connection=2 Write.*fua=1' fua5.log
+grep 'connection=1 Zero.*fua=0' fua5.log
+grep 'connection=2 Zero.*fua=1' fua5.log
-- 
2.25.0