[Libguestfs] [PATCH libnbd 7/7] api: Remove the valid_flag from all callbacks.

Richard W.M. Jones rjones at redhat.com
Mon Aug 12 16:08:51 UTC 2019


The freeing feature can now be done by associating a free callback
with a closure's user_data, so having the valid_flag is no longer
necessary and it can be completely removed.

This mostly reverts commit 2d9b98e96772e282d51dafac07f16387dadc8afa.
---
 TODO                                |   2 -
 docs/libnbd.pod                     |  64 ++--------------
 examples/glib-main-loop.c           |  14 +---
 examples/strict-structured-reads.c  |  63 +++++++---------
 generator/generator                 |  84 +++++++++------------
 generator/states-reply-simple.c     |   3 +-
 generator/states-reply-structured.c |  45 ++++--------
 generator/states-reply.c            |   3 +-
 generator/states.c                  |   3 +-
 interop/dirty-bitmap.c              |   5 +-
 interop/structured-read.c           |   5 +-
 lib/aio.c                           |  11 ---
 lib/debug.c                         |   7 +-
 lib/handle.c                        |   4 +-
 tests/closure-lifetimes.c           | 109 +++++++++++++++++-----------
 tests/meta-base-allocation.c        |   7 +-
 tests/oldstyle.c                    |   5 +-
 tests/server-death.c                |   5 +-
 18 files changed, 165 insertions(+), 274 deletions(-)

diff --git a/TODO b/TODO
index 8e067c0..03fda1f 100644
--- a/TODO
+++ b/TODO
@@ -26,8 +26,6 @@ Improve function trace output so that:
 Suggested API improvements:
   general:
   - synchronous APIs that have a timeout or can be cancelled
-  - separate free_callback corresponding to every Closure
-    (instead of using valid_flag)
 
   connecting:
   - nbd_connect_tcp: allow control over whether IPv4 or IPv6 is desired
diff --git a/docs/libnbd.pod b/docs/libnbd.pod
index 51b1a03..0068b84 100644
--- a/docs/libnbd.pod
+++ b/docs/libnbd.pod
@@ -608,59 +608,6 @@ as the second parameter to the callback.  The opaque pointer is only
 used from the C API, since in other languages you can use closures to
 achieve the same outcome.
 
-=head2 Callback lifetimes
-
-All callbacks have an C<unsigned valid_flag> parameter which is used
-to help with the lifetime of the callback.  C<valid_flag> contains the
-I<logical or> of:
-
-=over 4
-
-=item C<LIBNBD_CALLBACK_VALID>
-
-The callback parameters are valid and this is a normal callback.
-
-=item C<LIBNBD_CALLBACK_FREE>
-
-This is the last time the library will call this function.  Any data
-associated with the callback can be freed.
-
-=item other bits
-
-Other bits in C<valid_flag> should be ignored.
-
-=back
-
-For example C<nbd_set_debug_callback> sets up a callback which you
-could define like this:
-
- int my_debug_fn (unsigned valid_flag, void *user_data,
-                  const char *context, const char *msg)
- {
-   if (valid_flag & LIBNBD_CALLBACK_VALID) {
-     printf ("context = %s, msg = %s\n", context, msg);
-   }
-   if (valid_flag & LIBNBD_CALLBACK_FREE) {
-     /* If you need to free something, for example: */
-     free (user_data);
-   }
-   return 0;
- }
-
-If you don't care about the freeing feature then it is also correct to
-write this:
-
- int my_debug_fn (unsigned valid_flag, void *user_data,
-                  const char *context, const char *msg)
- {
-   if (!(valid_flag & LIBNBD_CALLBACK_VALID)) return 0;
-
-   // Rest of callback as normal.
- }
-
-The valid flag is only present in the C API.  It is not needed when
-using garbage-collected programming languages.
-
 =head2 Callbacks and locking
 
 The callbacks are invoked at a point where the libnbd lock is held; as
@@ -673,10 +620,10 @@ All of the low-level commands have a completion callback variant that
 registers a callback function used right before the command is marked
 complete.
 
-When C<valid_flag> includes C<LIBNBD_CALLBACK_VALID>, and the
-completion callback returns C<1>, the command is automatically retired
-(there is no need to call C<nbd_aio_command_completed>); for any other
-return value, the command still needs to be retired.
+When the completion callback returns C<1>, the command is
+automatically retired (there is no need to call
+C<nbd_aio_command_completed>); for any other return value, the command
+still needs to be retired.
 
 =head2 Callbacks with C<int *error> parameter
 
@@ -688,8 +635,7 @@ all of the completion callbacks, include a parameter C<error>
 containing the value of any error detected so far; if the callback
 function fails, it should assign back into C<error> and return C<-1>
 to change the resulting error of the overall command.  Assignments
-into C<error> are ignored for any other return value or when
-C<valid_flag> did not contain C<LIBNBD_CALLBACK_VALID>; similarly,
+into C<error> are ignored for any other return value; similarly,
 assigning C<0> into C<error> does not have an effect.
 
 =head1 SEE ALSO
diff --git a/examples/glib-main-loop.c b/examples/glib-main-loop.c
index 05a59e3..216eb5e 100644
--- a/examples/glib-main-loop.c
+++ b/examples/glib-main-loop.c
@@ -268,9 +268,9 @@ static GMainLoop *loop;
 
 static void connected (struct NBDSource *source);
 static gboolean read_data (gpointer user_data);
-static int finished_read (unsigned valid_flag, void *vp, int *error);
+static int finished_read (void *vp, int *error);
 static gboolean write_data (gpointer user_data);
-static int finished_write (unsigned valid_flag, void *vp, int *error);
+static int finished_write (void *vp, int *error);
 
 int
 main (int argc, char *argv[])
@@ -394,13 +394,10 @@ read_data (gpointer user_data)
 
 /* This callback is called from libnbd when any read command finishes. */
 static int
-finished_read (unsigned valid_flag, void *vp, int *error)
+finished_read (void *vp, int *error)
 {
   struct buffer *buffer = vp;
 
-  if (!(valid_flag & LIBNBD_CALLBACK_VALID))
-    return 0;
-
   if (gssrc == NULL)
     return 0;
 
@@ -442,13 +439,10 @@ write_data (gpointer user_data)
 
 /* This callback is called from libnbd when any write command finishes. */
 static int
-finished_write (unsigned valid_flag, void *vp, int *error)
+finished_write (void *vp, int *error)
 {
   struct buffer *buffer = vp;
 
-  if (!(valid_flag & LIBNBD_CALLBACK_VALID))
-    return 0;
-
   if (gsdest == NULL)
     return 0;
 
diff --git a/examples/strict-structured-reads.c b/examples/strict-structured-reads.c
index b3880b7..701b216 100644
--- a/examples/strict-structured-reads.c
+++ b/examples/strict-structured-reads.c
@@ -51,16 +51,13 @@ static int64_t total_bytes;
 static int total_success;
 
 static int
-read_chunk (unsigned valid_flag, void *opaque,
+read_chunk (void *opaque,
             const void *bufv, size_t count, uint64_t offset,
             unsigned status, int *error)
 {
   struct data *data = opaque;
   struct range *r, **prev;
 
-  if (!(valid_flag & LIBNBD_CALLBACK_VALID))
-    return 0;
-
   /* libnbd guarantees this: */
   assert (offset >= data->offset);
   assert (offset + count <= data->offset + data->count);
@@ -131,46 +128,41 @@ read_chunk (unsigned valid_flag, void *opaque,
 }
 
 static int
-read_verify (unsigned valid_flag, void *opaque, int *error)
+read_verify (void *opaque, int *error)
 {
   int ret = 0;
 
-  if (valid_flag & LIBNBD_CALLBACK_VALID) {
-    struct data *data = opaque;
+  struct data *data = opaque;
 
-    ret = -1;
-    total_reads++;
-    total_chunks += data->chunks;
-    if (*error)
-      goto cleanup;
-    assert (data->chunks > 0);
-    if (data->flags & LIBNBD_CMD_FLAG_DF) {
-      total_df_reads++;
-      if (data->chunks > 1) {
-        fprintf (stderr, "buggy server: too many chunks for DF flag\n");
-        *error = EPROTO;
-        goto cleanup;
-      }
-    }
-    if (data->remaining && !*error) {
-      fprintf (stderr, "buggy server: not enough chunks on success\n");
+  ret = -1;
+  total_reads++;
+  total_chunks += data->chunks;
+  if (*error)
+    goto cleanup;
+  assert (data->chunks > 0);
+  if (data->flags & LIBNBD_CMD_FLAG_DF) {
+    total_df_reads++;
+    if (data->chunks > 1) {
+      fprintf (stderr, "buggy server: too many chunks for DF flag\n");
       *error = EPROTO;
       goto cleanup;
     }
-    total_bytes += data->count;
-    total_success++;
-    ret = 0;
-
-  cleanup:
-    while (data->remaining) {
-      struct range *r = data->remaining;
-      data->remaining = r->next;
-      free (r);
-    }
   }
+  if (data->remaining && !*error) {
+    fprintf (stderr, "buggy server: not enough chunks on success\n");
+    *error = EPROTO;
+    goto cleanup;
+  }
+  total_bytes += data->count;
+  total_success++;
+  ret = 0;
 
-  if (valid_flag & LIBNBD_CALLBACK_FREE)
-    free (opaque);
+ cleanup:
+  while (data->remaining) {
+    struct range *r = data->remaining;
+    data->remaining = r->next;
+    free (r);
+  }
 
   return ret;
 }
@@ -235,6 +227,7 @@ main (int argc, char *argv[])
     *r = (struct range) { .first = offset, .last = offset + maxsize, };
     *d = (struct data) { .offset = offset, .count = maxsize, .flags = flags,
                          .remaining = r, };
+    /* XXX *d and *r are both leaked. */
     if (nbd_aio_pread_structured_callback (nbd, buf, sizeof buf, offset,
                                            read_chunk, d, read_verify, d,
                                            flags) == -1) {
diff --git a/generator/generator b/generator/generator
index a0322ee..0187c02 100755
--- a/generator/generator
+++ b/generator/generator
@@ -3190,7 +3190,7 @@ module C : sig
   val generate_docs_libnbd_api_pod : unit -> unit
   val print_arg_list : ?handle:bool -> ?types:bool ->
                        arg list -> optarg list -> unit
-  val print_cbarg_list : ?valid_flag:bool -> ?types:bool -> cbarg list -> unit
+  val print_cbarg_list : ?types:bool -> cbarg list -> unit
   val errcode_of_ret : ret -> string option
   val type_of_ret : ret -> string
 end = struct
@@ -3430,13 +3430,8 @@ let print_extern name args optargs ret =
   print_call name args optargs ret;
   pr ";\n"
 
-let print_cbarg_list ?(valid_flag = true) ?(types = true) cbargs =
+let print_cbarg_list ?(types = true) cbargs =
   pr "(";
-  if valid_flag then (
-    if types then pr "unsigned ";
-    pr "valid_flag";
-    pr ", ";
-  );
   if types then pr "void *";
   pr "user_data";
 
@@ -3567,9 +3562,6 @@ let generate_include_libnbd_h () =
       pr "#define %-40s %d\n" n i
   ) constants;
   pr "\n";
-  pr "#define LIBNBD_CALLBACK_VALID 1\n";
-  pr "#define LIBNBD_CALLBACK_FREE  2\n";
-  pr "\n";
   pr "extern struct nbd_handle *nbd_create (void);\n";
   pr "#define LIBNBD_HAVE_NBD_CREATE 1\n";
   pr "\n";
@@ -4226,26 +4218,25 @@ let print_python_binding name { args; optargs; ret; may_set_error } =
        pr "{\n";
        pr "  int ret = 0;\n";
        pr "\n";
-       pr "  if (valid_flag & LIBNBD_CALLBACK_VALID) {\n";
-       pr "    PyGILState_STATE py_save = PyGILState_UNLOCKED;\n";
-       pr "    PyObject *py_args, *py_ret;\n";
+       pr "  PyGILState_STATE py_save = PyGILState_UNLOCKED;\n";
+       pr "  PyObject *py_args, *py_ret;\n";
        List.iter (
          function
          | CBArrayAndLen (UInt32 n, len) ->
-            pr "    PyObject *py_%s = PyList_New (%s);\n" n len;
-            pr "    for (size_t i = 0; i < %s; ++i)\n" len;
-            pr "      PyList_SET_ITEM (py_%s, i, PyLong_FromUnsignedLong (%s[i]));\n" n n
+            pr "  PyObject *py_%s = PyList_New (%s);\n" n len;
+            pr "  for (size_t i = 0; i < %s; ++i)\n" len;
+            pr "    PyList_SET_ITEM (py_%s, i, PyLong_FromUnsignedLong (%s[i]));\n" n n
          | CBBytesIn _
          | CBInt _
          | CBInt64 _ -> ()
          | CBMutable (Int n) ->
-            pr "    PyObject *py_%s_modname = PyUnicode_FromString (\"ctypes\");\n" n;
-            pr "    if (!py_%s_modname) { PyErr_PrintEx (0); return -1; }\n" n;
-            pr "    PyObject *py_%s_mod = PyImport_Import (py_%s_modname);\n" n n;
-            pr "    Py_DECREF (py_%s_modname);\n" n;
-            pr "    if (!py_%s_mod) { PyErr_PrintEx (0); return -1; }\n" n;
-            pr "    PyObject *py_%s = PyObject_CallMethod (py_%s_mod, \"c_int\", \"i\", *%s);\n" n n n;
-            pr "    if (!py_%s) { PyErr_PrintEx (0); return -1; }\n" n;
+            pr "  PyObject *py_%s_modname = PyUnicode_FromString (\"ctypes\");\n" n;
+            pr "  if (!py_%s_modname) { PyErr_PrintEx (0); return -1; }\n" n;
+            pr "  PyObject *py_%s_mod = PyImport_Import (py_%s_modname);\n" n n;
+            pr "  Py_DECREF (py_%s_modname);\n" n;
+            pr "  if (!py_%s_mod) { PyErr_PrintEx (0); return -1; }\n" n;
+            pr "  PyObject *py_%s = PyObject_CallMethod (py_%s_mod, \"c_int\", \"i\", *%s);\n" n n n;
+            pr "  if (!py_%s) { PyErr_PrintEx (0); return -1; }\n" n;
          | CBString _
          | CBUInt _
          | CBUInt64 _ -> ()
@@ -4253,7 +4244,7 @@ let print_python_binding name { args; optargs; ret; may_set_error } =
        ) cbargs;
        pr "\n";
 
-       pr "    py_args = Py_BuildValue (\"(\"";
+       pr "  py_args = Py_BuildValue (\"(\"";
        List.iter (
          function
          | CBArrayAndLen (UInt32 n, len) -> pr " \"O\""
@@ -4278,42 +4269,41 @@ let print_python_binding name { args; optargs; ret; may_set_error } =
          | CBArrayAndLen _ | CBMutable _ -> assert false
        ) cbargs;
        pr ");\n";
-       pr "    Py_INCREF (py_args);\n";
+       pr "  Py_INCREF (py_args);\n";
        pr "\n";
-       pr "    if (PyEval_ThreadsInitialized ())\n";
-       pr "      py_save = PyGILState_Ensure ();\n";
+       pr "  if (PyEval_ThreadsInitialized ())\n";
+       pr "    py_save = PyGILState_Ensure ();\n";
        pr "\n";
-       pr "    py_ret = PyObject_CallObject ((PyObject *)user_data, py_args);\n";
+       pr "  py_ret = PyObject_CallObject ((PyObject *)user_data, py_args);\n";
        pr "\n";
-       pr "    if (PyEval_ThreadsInitialized ())\n";
-       pr "      PyGILState_Release (py_save);\n";
+       pr "  if (PyEval_ThreadsInitialized ())\n";
+       pr "    PyGILState_Release (py_save);\n";
        pr "\n";
-       pr "    Py_DECREF (py_args);\n";
+       pr "  Py_DECREF (py_args);\n";
        pr "\n";
-       pr "    if (py_ret != NULL) {\n";
-       pr "      Py_DECREF (py_ret); /* return value is discarded */\n";
-       pr "    }\n";
-       pr "    else {\n";
-       pr "      ret = -1;\n";
-       pr "      PyErr_PrintEx (0); /* print exception */\n";
-       pr "    };\n";
+       pr "  if (py_ret != NULL) {\n";
+       pr "    Py_DECREF (py_ret); /* return value is discarded */\n";
+       pr "  }\n";
+       pr "  else {\n";
+       pr "    ret = -1;\n";
+       pr "    PyErr_PrintEx (0); /* print exception */\n";
+       pr "  };\n";
        pr "\n";
        List.iter (
          function
          | CBArrayAndLen (UInt32 n, _) ->
-            pr "    Py_DECREF (py_%s);\n" n
+            pr "  Py_DECREF (py_%s);\n" n
          | CBMutable (Int n) ->
-            pr "    PyObject *py_%s_ret = PyObject_GetAttrString (py_%s, \"value\");\n" n n;
-            pr "    *%s = PyLong_AsLong (py_%s_ret);\n" n n;
-            pr "    Py_DECREF (py_%s_ret);\n" n;
-            pr "    Py_DECREF (py_%s);\n" n
+            pr "  PyObject *py_%s_ret = PyObject_GetAttrString (py_%s, \"value\");\n" n n;
+            pr "  *%s = PyLong_AsLong (py_%s_ret);\n" n n;
+            pr "  Py_DECREF (py_%s_ret);\n" n;
+            pr "  Py_DECREF (py_%s);\n" n
          | CBBytesIn _
          | CBInt _ | CBInt64 _
          | CBString _
          | CBUInt _ | CBUInt64 _ -> ()
          | CBArrayAndLen _ | CBMutable _ -> assert false
        ) cbargs;
-       pr "  }\n";
        pr "\n";
        pr "  return ret;\n";
        pr "}\n";
@@ -5159,7 +5149,7 @@ let print_ocaml_binding (name, { args; optargs; ret }) =
        pr "/* Wrapper for %s callback of %s. */\n" cbname name;
        pr "static int\n";
        pr "%s_%s_wrapper_locked " name cbname;
-       C.print_cbarg_list ~valid_flag:false cbargs;
+       C.print_cbarg_list cbargs;
        pr "\n";
        pr "{\n";
        pr "  CAMLparam0 ();\n";
@@ -5239,13 +5229,11 @@ let print_ocaml_binding (name, { args; optargs; ret }) =
        pr "{\n";
        pr "  int ret = 0;\n";
        pr "\n";
-       pr "  if (valid_flag & LIBNBD_CALLBACK_VALID) {\n";
        pr "  caml_leave_blocking_section ();\n";
        pr "  ret = %s_%s_wrapper_locked " name cbname;
-       C.print_cbarg_list ~valid_flag:false ~types:false cbargs;
+       C.print_cbarg_list ~types:false cbargs;
        pr ";\n";
        pr "  caml_enter_blocking_section ();\n";
-       pr "  }\n";
        pr "\n";
        pr "  return ret;\n";
        pr "}\n";
diff --git a/generator/states-reply-simple.c b/generator/states-reply-simple.c
index 9684bc4..11354e5 100644
--- a/generator/states-reply-simple.c
+++ b/generator/states-reply-simple.c
@@ -64,8 +64,7 @@
       int error = 0;
 
       assert (cmd->error == 0);
-      if (cmd->cb.fn.chunk (LIBNBD_CALLBACK_VALID|LIBNBD_CALLBACK_FREE,
-                            cmd->cb.fn_user_data,
+      if (cmd->cb.fn.chunk (cmd->cb.fn_user_data,
                             cmd->data, cmd->count,
                             cmd->offset, LIBNBD_READ_DATA, &error) == -1)
         cmd->error = error ? error : EPROTO;
diff --git a/generator/states-reply-structured.c b/generator/states-reply-structured.c
index b016cd7..846cc35 100644
--- a/generator/states-reply-structured.c
+++ b/generator/states-reply-structured.c
@@ -18,17 +18,6 @@
 
 /* State machine for parsing structured replies from the server. */
 
-static unsigned
-valid_flags (struct nbd_handle *h)
-{
-  unsigned valid = LIBNBD_CALLBACK_VALID;
-  uint16_t flags = be16toh (h->sbuf.sr.structured_reply.flags);
-
-  if (flags & NBD_REPLY_FLAG_DONE)
-    valid |= LIBNBD_CALLBACK_FREE;
-  return valid;
-}
-
 /*----- End of prologue. -----*/
 
 /* STATE MACHINE */ {
@@ -306,18 +295,18 @@ valid_flags (struct nbd_handle *h)
       }
       if (cmd->type == NBD_CMD_READ && cmd->cb.fn.chunk) {
         int scratch = error;
-        unsigned valid = valid_flags (h);
+        uint16_t flags = be16toh (h->sbuf.sr.structured_reply.flags);
 
         /* Different from successful reads: inform the callback about the
          * current error rather than any earlier one. If the callback fails
          * without setting errno, then use the server's error below.
          */
-        if (cmd->cb.fn.chunk (valid, cmd->cb.fn_user_data,
+        if (cmd->cb.fn.chunk (cmd->cb.fn_user_data,
                               cmd->data + (offset - cmd->offset),
                               0, offset, LIBNBD_READ_ERROR, &scratch) == -1)
           if (cmd->error == 0)
             cmd->error = scratch;
-        if (valid & LIBNBD_CALLBACK_FREE) {
+        if (flags & NBD_REPLY_FLAG_DONE) {
           cmd->cb.fn.chunk = NULL; /* because we've freed it */
           nbd_internal_free_callback (h, cmd->cb.fn_user_data);
         }
@@ -402,15 +391,15 @@ valid_flags (struct nbd_handle *h)
     assert (cmd); /* guaranteed by CHECK */
     if (cmd->cb.fn.chunk) {
       int error = cmd->error;
-      unsigned valid = valid_flags (h);
+      uint16_t flags = be16toh (h->sbuf.sr.structured_reply.flags);
 
-      if (cmd->cb.fn.chunk (valid, cmd->cb.fn_user_data,
+      if (cmd->cb.fn.chunk (cmd->cb.fn_user_data,
                             cmd->data + (offset - cmd->offset),
                             length - sizeof offset, offset,
                            LIBNBD_READ_DATA, &error) == -1)
         if (cmd->error == 0)
           cmd->error = error ? error : EPROTO;
-      if (valid & LIBNBD_CALLBACK_FREE) {
+      if (flags & NBD_REPLY_FLAG_DONE) {
         cmd->cb.fn.chunk = NULL; /* because we've freed it */
         nbd_internal_free_callback (h, cmd->cb.fn_user_data);
       }
@@ -469,15 +458,15 @@ valid_flags (struct nbd_handle *h)
     memset (cmd->data + offset, 0, length);
     if (cmd->cb.fn.chunk) {
       int error = cmd->error;
-      unsigned valid = valid_flags (h);
+      uint16_t flags = be16toh (h->sbuf.sr.structured_reply.flags);
 
-      if (cmd->cb.fn.chunk (valid, cmd->cb.fn_user_data,
+      if (cmd->cb.fn.chunk (cmd->cb.fn_user_data,
                             cmd->data + offset, length,
                             cmd->offset + offset,
                             LIBNBD_READ_HOLE, &error) == -1)
         if (cmd->error == 0)
           cmd->error = error ? error : EPROTO;
-      if (valid & LIBNBD_CALLBACK_FREE) {
+      if (flags & NBD_REPLY_FLAG_DONE) {
         cmd->cb.fn.chunk = NULL; /* because we've freed it */
         nbd_internal_free_callback (h, cmd->cb.fn_user_data);
       }
@@ -526,14 +515,14 @@ valid_flags (struct nbd_handle *h)
     if (meta_context) {
       /* Call the caller's extent function. */
       int error = cmd->error;
-      unsigned valid = valid_flags (h);
+      uint16_t flags = be16toh (h->sbuf.sr.structured_reply.flags);
 
-      if (cmd->cb.fn.extent (valid, cmd->cb.fn_user_data,
+      if (cmd->cb.fn.extent (cmd->cb.fn_user_data,
                              meta_context->name, cmd->offset,
                              &h->bs_entries[1], (length-4) / 4, &error) == -1)
         if (cmd->error == 0)
           cmd->error = error ? error : EPROTO;
-      if (valid & LIBNBD_CALLBACK_FREE) {
+      if (flags & NBD_REPLY_FLAG_DONE) {
         cmd->cb.fn.extent = NULL; /* because we've freed it */
         nbd_internal_free_callback (h, cmd->cb.fn_user_data);
       }
@@ -553,16 +542,10 @@ valid_flags (struct nbd_handle *h)
 
   flags = be16toh (h->sbuf.sr.structured_reply.flags);
   if (flags & NBD_REPLY_FLAG_DONE) {
-    if (cmd->type == NBD_CMD_BLOCK_STATUS && cmd->cb.fn.extent) {
-      cmd->cb.fn.extent (LIBNBD_CALLBACK_FREE, cmd->cb.fn_user_data,
-                         NULL, 0, NULL, 0, NULL);
+    if (cmd->type == NBD_CMD_BLOCK_STATUS && cmd->cb.fn.extent)
       nbd_internal_free_callback (h, cmd->cb.fn_user_data);
-    }
-    if (cmd->type == NBD_CMD_READ && cmd->cb.fn.chunk) {
-      cmd->cb.fn.chunk (LIBNBD_CALLBACK_FREE, cmd->cb.fn_user_data,
-                        NULL, 0, 0, 0, NULL);
+    if (cmd->type == NBD_CMD_READ && cmd->cb.fn.chunk)
       nbd_internal_free_callback (h, cmd->cb.fn_user_data);
-    }
     cmd->cb.fn.chunk = NULL;
     SET_NEXT_STATE (%^FINISH_COMMAND);
   }
diff --git a/generator/states-reply.c b/generator/states-reply.c
index d5cba1a..1e0e92c 100644
--- a/generator/states-reply.c
+++ b/generator/states-reply.c
@@ -173,8 +173,7 @@ save_reply_state (struct nbd_handle *h)
     int r;
 
     assert (cmd->type != NBD_CMD_DISC);
-    r = cmd->cb.completion (LIBNBD_CALLBACK_VALID|LIBNBD_CALLBACK_FREE,
-                            cmd->cb.user_data, &error);
+    r = cmd->cb.completion (cmd->cb.user_data, &error);
     nbd_internal_free_callback (h, cmd->cb.user_data);
     cmd->cb.completion = NULL; /* because we've freed it */
     switch (r) {
diff --git a/generator/states.c b/generator/states.c
index 313d2c9..4d3a93c 100644
--- a/generator/states.c
+++ b/generator/states.c
@@ -126,8 +126,7 @@ void abort_commands (struct nbd_handle *h,
       int r;
 
       assert (cmd->type != NBD_CMD_DISC);
-      r = cmd->cb.completion (LIBNBD_CALLBACK_VALID|LIBNBD_CALLBACK_FREE,
-                              cmd->cb.user_data, &error);
+      r = cmd->cb.completion (cmd->cb.user_data, &error);
       nbd_internal_free_callback (h, cmd->cb.user_data);
       cmd->cb.completion = NULL; /* because we've freed it */
       switch (r) {
diff --git a/interop/dirty-bitmap.c b/interop/dirty-bitmap.c
index aca0564..fbd6f29 100644
--- a/interop/dirty-bitmap.c
+++ b/interop/dirty-bitmap.c
@@ -42,14 +42,11 @@ struct data {
 };
 
 static int
-cb (unsigned valid_flag, void *opaque, const char *metacontext, uint64_t offset,
+cb (void *opaque, const char *metacontext, uint64_t offset,
     uint32_t *entries, size_t len, int *error)
 {
   struct data *data = opaque;
 
-  if (!(valid_flag & LIBNBD_CALLBACK_VALID))
-    return 0;
-
   /* libnbd does not actually verify that a server is fully compliant
    * to the spec; the asserts marked [qemu-nbd] are thus dependent on
    * the fact that qemu-nbd is compliant.
diff --git a/interop/structured-read.c b/interop/structured-read.c
index 0b189d1..3e62b05 100644
--- a/interop/structured-read.c
+++ b/interop/structured-read.c
@@ -48,16 +48,13 @@ struct data {
 };
 
 static int
-read_cb (unsigned valid_flag, void *opaque,
+read_cb (void *opaque,
          const void *bufv, size_t count, uint64_t offset,
          unsigned status, int *error)
 {
   struct data *data = opaque;
   const char *buf = bufv;
 
-  if (!(valid_flag & LIBNBD_CALLBACK_VALID))
-    return 0;
-
   /* The NBD spec allows chunks to be reordered; we are relying on the
    * fact that qemu-nbd does not do so.
    */
diff --git a/lib/aio.c b/lib/aio.c
index 8aa4547..4cc61cb 100644
--- a/lib/aio.c
+++ b/lib/aio.c
@@ -32,17 +32,6 @@ void
 nbd_internal_retire_and_free_command (struct nbd_handle *h,
                                       struct command *cmd)
 {
-  /* Free the callbacks. */
-  if (cmd->type == NBD_CMD_BLOCK_STATUS && cmd->cb.fn.extent)
-    cmd->cb.fn.extent (LIBNBD_CALLBACK_FREE, cmd->cb.fn_user_data,
-                       NULL, 0, NULL, 0, NULL);
-  if (cmd->type == NBD_CMD_READ && cmd->cb.fn.chunk)
-    cmd->cb.fn.chunk (LIBNBD_CALLBACK_FREE, cmd->cb.fn_user_data,
-                      NULL, 0, 0, 0, NULL);
-  if (cmd->cb.completion)
-    cmd->cb.completion (LIBNBD_CALLBACK_FREE, cmd->cb.user_data,
-                        NULL);
-
   /* Free the closures if there's an associated free callback. */
   nbd_internal_free_callback (h, cmd->cb.fn_user_data);
   nbd_internal_free_callback (h, cmd->cb.user_data);
diff --git a/lib/debug.c b/lib/debug.c
index 34d4184..bd0c465 100644
--- a/lib/debug.c
+++ b/lib/debug.c
@@ -42,11 +42,8 @@ int
 nbd_unlocked_set_debug_callback (struct nbd_handle *h,
                                  nbd_debug_callback debug_callback, void *data)
 {
-  if (h->debug_callback) {
-    /* ignore return value */
-    h->debug_callback (LIBNBD_CALLBACK_FREE, h->debug_data, NULL, NULL);
+  if (h->debug_callback)
     nbd_internal_free_callback (h, h->debug_data);
-  }
   h->debug_callback = debug_callback;
   h->debug_data = data;
   return 0;
@@ -80,7 +77,7 @@ nbd_internal_debug (struct nbd_handle *h, const char *fs, ...)
 
   if (h->debug_callback)
     /* ignore return value */
-    h->debug_callback (LIBNBD_CALLBACK_VALID, h->debug_data, context, msg);
+    h->debug_callback (h->debug_data, context, msg);
   else
     fprintf (stderr, "libnbd: debug: %s: %s: %s\n",
              h->hname, context ? : "unknown", msg);
diff --git a/lib/handle.c b/lib/handle.c
index 5a47bd8..4c59622 100644
--- a/lib/handle.c
+++ b/lib/handle.c
@@ -113,10 +113,8 @@ nbd_close (struct nbd_handle *h)
     return;
 
   /* Free user callbacks first. */
-  if (h->debug_callback) {
-    h->debug_callback (LIBNBD_CALLBACK_FREE, h->debug_data, NULL, NULL);
+  if (h->debug_callback)
     nbd_internal_free_callback (h, h->debug_data);
-  }
   h->debug_callback = NULL;
 
   free (h->bs_entries);
diff --git a/tests/closure-lifetimes.c b/tests/closure-lifetimes.c
index d8ea3f7..c1815b0 100644
--- a/tests/closure-lifetimes.c
+++ b/tests/closure-lifetimes.c
@@ -38,50 +38,59 @@ static char *nbdkit_delay[] =
     "delay-read=10",
     NULL };
 
-static unsigned debug_fn_valid;
-static unsigned debug_fn_free;
-static unsigned read_cb_valid;
-static unsigned read_cb_free;
-static unsigned completion_cb_valid;
-static unsigned completion_cb_free;
+static unsigned debug_fn_called;
+static unsigned debug_fn_freed;
+static unsigned read_cb_called;
+static unsigned read_cb_freed;
+static unsigned completion_cb_called;
+static unsigned completion_cb_freed;
 
 static int
-debug_fn (unsigned valid_flag, void *opaque,
+debug_fn (void *opaque,
           const char *context, const char *msg)
 {
-  if (valid_flag & LIBNBD_CALLBACK_VALID)
-    debug_fn_valid++;
-  if (valid_flag & LIBNBD_CALLBACK_FREE)
-    debug_fn_free++;
+  debug_fn_called++;
   return 0;
 }
 
+static void
+debug_fn_free (void *ptr, void *opaque)
+{
+  debug_fn_freed++;
+}
+
 static int
-read_cb (unsigned valid_flag, void *opaque,
+read_cb (void *opaque,
          const void *subbuf, size_t count,
          uint64_t offset, unsigned status, int *error)
 {
-  assert (read_cb_free == 0);
+  assert (read_cb_freed == 0);
 
-  if (valid_flag & LIBNBD_CALLBACK_VALID)
-    read_cb_valid++;
-  if (valid_flag & LIBNBD_CALLBACK_FREE)
-    read_cb_free++;
+  read_cb_called++;
   return 0;
 }
 
+static void
+read_cb_free (void *ptr, void *opaque)
+{
+  read_cb_freed++;
+}
+
 static int
-completion_cb (unsigned valid_flag, void *opaque, int *error)
+completion_cb (void *opaque, int *error)
 {
-  assert (completion_cb_free == 0);
+  assert (completion_cb_freed == 0);
 
-  if (valid_flag & LIBNBD_CALLBACK_VALID)
-    completion_cb_valid++;
-  if (valid_flag & LIBNBD_CALLBACK_FREE)
-    completion_cb_free++;
+  completion_cb_called++;
   return 0;
 }
 
+static void
+completion_cb_free (void *ptr, void *opaque)
+{
+  completion_cb_freed++;
+}
+
 #define NBD_ERROR                                               \
   do {                                                          \
     fprintf (stderr, "%s: %s\n", argv[0], nbd_get_error ());    \
@@ -101,35 +110,44 @@ main (int argc, char *argv[])
   nbd = nbd_create ();
   if (nbd == NULL) NBD_ERROR;
 
-  nbd_set_debug_callback (nbd, debug_fn, NULL);
-  assert (debug_fn_free == 0);
+  if (nbd_add_free_callback (nbd, &debug_fn, debug_fn_free, NULL) == -1)
+    NBD_ERROR;
+  nbd_set_debug_callback (nbd, debug_fn, &debug_fn);
+  assert (debug_fn_freed == 0);
 
-  nbd_set_debug_callback (nbd, debug_fn, NULL);
-  assert (debug_fn_free == 1);
+  if (nbd_add_free_callback (nbd, &debug_fn, debug_fn_free, NULL) == -1)
+    NBD_ERROR;
+  nbd_set_debug_callback (nbd, debug_fn, &debug_fn);
+  assert (debug_fn_freed == 1);
 
-  debug_fn_free = 0;
+  debug_fn_freed = 0;
   nbd_close (nbd);
-  assert (debug_fn_free == 1);
+  assert (debug_fn_freed == 1);
 
   /* Test command callbacks are freed when the command is retired. */
   nbd = nbd_create ();
   if (nbd == NULL) NBD_ERROR;
   if (nbd_connect_command (nbd, nbdkit) == -1) NBD_ERROR;
 
+  if (nbd_add_free_callback (nbd, &read_cb, read_cb_free, NULL) == -1)
+    NBD_ERROR;
+  if (nbd_add_free_callback (nbd, &completion_cb, completion_cb_free, NULL)
+      == -1)
+    NBD_ERROR;
   cookie = nbd_aio_pread_structured_callback (nbd, buf, sizeof buf, 0,
-                                              read_cb, NULL,
-                                              completion_cb, NULL, 0);
+                                              read_cb, &read_cb,
+                                              completion_cb, &completion_cb, 0);
   if (cookie == -1) NBD_ERROR;
-  assert (read_cb_free == 0);
-  assert (completion_cb_free == 0);
+  assert (read_cb_freed == 0);
+  assert (completion_cb_freed == 0);
   while (!nbd_aio_command_completed (nbd, cookie)) {
     if (nbd_poll (nbd, -1) == -1) NBD_ERROR;
   }
 
-  assert (read_cb_valid == 1);
-  assert (completion_cb_valid == 1);
-  assert (read_cb_free == 1);
-  assert (completion_cb_free == 1);
+  assert (read_cb_called == 1);
+  assert (completion_cb_called == 1);
+  assert (read_cb_freed == 1);
+  assert (completion_cb_freed == 1);
 
   nbd_kill_command (nbd, 0);
   nbd_close (nbd);
@@ -137,21 +155,26 @@ main (int argc, char *argv[])
   /* Test command callbacks are freed if the handle is closed without
    * running the commands.
    */
-  read_cb_valid = read_cb_free =
-    completion_cb_valid = completion_cb_free = 0;
+  read_cb_called = read_cb_freed =
+    completion_cb_called = completion_cb_freed = 0;
   nbd = nbd_create ();
   if (nbd == NULL) NBD_ERROR;
   if (nbd_connect_command (nbd, nbdkit_delay) == -1) NBD_ERROR;
 
+  if (nbd_add_free_callback (nbd, &read_cb, read_cb_free, NULL) == -1)
+    NBD_ERROR;
+  if (nbd_add_free_callback (nbd, &completion_cb, completion_cb_free, NULL)
+      == -1)
+    NBD_ERROR;
   cookie = nbd_aio_pread_structured_callback (nbd, buf, sizeof buf, 0,
-                                              read_cb, NULL,
-                                              completion_cb, NULL, 0);
+                                              read_cb, &read_cb,
+                                              completion_cb, &completion_cb, 0);
   if (cookie == -1) NBD_ERROR;
   nbd_kill_command (nbd, 0);
   nbd_close (nbd);
 
-  assert (read_cb_free == 1);
-  assert (completion_cb_free == 1);
+  assert (read_cb_freed == 1);
+  assert (completion_cb_freed == 1);
 
   exit (EXIT_SUCCESS);
 }
diff --git a/tests/meta-base-allocation.c b/tests/meta-base-allocation.c
index c36a77f..0219ce9 100644
--- a/tests/meta-base-allocation.c
+++ b/tests/meta-base-allocation.c
@@ -30,7 +30,7 @@
 
 #include <libnbd.h>
 
-static int check_extent (unsigned valid_flag, void *data,
+static int check_extent (void *data,
                          const char *metacontext,
                          uint64_t offset,
                          uint32_t *entries, size_t nr_entries, int *error);
@@ -129,7 +129,7 @@ main (int argc, char *argv[])
 }
 
 static int
-check_extent (unsigned valid_flag, void *data,
+check_extent (void *data,
               const char *metacontext,
               uint64_t offset,
               uint32_t *entries, size_t nr_entries, int *error)
@@ -137,9 +137,6 @@ check_extent (unsigned valid_flag, void *data,
   size_t i;
   int id;
 
-  if (!(valid_flag & LIBNBD_CALLBACK_VALID))
-    return 0;
-
   id = * (int *)data;
 
   printf ("extent: id=%d, metacontext=%s, offset=%" PRIu64 ", "
diff --git a/tests/oldstyle.c b/tests/oldstyle.c
index afbda61..1382d06 100644
--- a/tests/oldstyle.c
+++ b/tests/oldstyle.c
@@ -37,15 +37,12 @@ static char wbuf[512] = { 1, 2, 3, 4 }, rbuf[512];
 static const char *progname;
 
 static int
-pread_cb (unsigned valid_flag, void *data,
+pread_cb (void *data,
           const void *buf, size_t count, uint64_t offset,
           unsigned status, int *error)
 {
   int *calls;
 
-  if (!(valid_flag & LIBNBD_CALLBACK_VALID))
-    return 0;
-
   calls = data;
   ++*calls;
 
diff --git a/tests/server-death.c b/tests/server-death.c
index 7854527..256b45a 100644
--- a/tests/server-death.c
+++ b/tests/server-death.c
@@ -33,11 +33,8 @@ static bool trim_retired;
 static const char *progname;
 
 static int
-callback (unsigned valid_flag, void *ignored, int *error)
+callback (void *ignored, int *error)
 {
-  if (!(valid_flag & LIBNBD_CALLBACK_VALID))
-    return 0;
-
   if (*error != ENOTCONN) {
     fprintf (stderr, "%s: unexpected error in trim callback: %s\n",
              progname, strerror (*error));
-- 
2.22.0




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