block: Add no_coroutine_fn and coroutine_mixed_fn marker

Add more annotations to functions, describing valid and invalid
calls from coroutine to non-coroutine context.

When applied to a function, no_coroutine_fn advertises that it should
not be called from coroutine_fn functions.  This can be because the
function blocks or, in the case of generated_co_wrapper, to enforce
that coroutine_fn functions directly call the coroutine_fn that backs
the generated_co_wrapper.

coroutine_mixed_fn instead is for function that can be called in
both coroutine and non-coroutine context, but will suspend when
called in coroutine context.  Annotating them is a first step
towards enforcing that non-annotated functions are absolutely
not going to suspend.

These can be used for example with the vrc tool:

    # find functions that *really* cannot be called from no_coroutine_fn
    (vrc) load --loader clang libblock.fa.p/meson-generated_.._block_block-gen.c.o
    (vrc) paths [no_coroutine_fn,!coroutine_mixed_fn]
    bdrv_remove_persistent_dirty_bitmap
    bdrv_create
    bdrv_can_store_new_dirty_bitmap

    # find how coroutine_fns end up calling a mixed function
    (vrc) load --loader clang --force libblock.fa.p/*.c.o
    (vrc) paths [coroutine_fn] [!no_coroutine_fn]* [coroutine_mixed_fn]
    ...
    bdrv_pread <- vhdx_log_write <- vhdx_log_write_and_flush <- vhdx_co_writev
    ...

Signed-off-by: Alberto Faria <afaria@redhat.com>
[Rebase, add coroutine_mixed_fn. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20221216110758.559947-3-pbonzini@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

1 files changed, 7 insertions, 4 deletions

diff --git a/include/block/block-common.h b/include/block/block-common.h
index 4168681..469300f 100644
--- a/include/block/block-common.h
+++ b/include/block/block-common.h
@@ -45,11 +45,14 @@
  * - co_wrapper_mixed_bdrv_rdlock are co_wrapper_mixed functions but
  *   automatically take and release the graph rdlock when creating a new
  *   coroutine.
+ *
+ * These functions should not be called from a coroutine_fn; instead,
+ * call the wrapped function directly.
  */
-#define co_wrapper
-#define co_wrapper_mixed
-#define co_wrapper_bdrv_rdlock
-#define co_wrapper_mixed_bdrv_rdlock
+#define co_wrapper                     no_coroutine_fn
+#define co_wrapper_mixed               no_coroutine_fn coroutine_mixed_fn
+#define co_wrapper_bdrv_rdlock         no_coroutine_fn
+#define co_wrapper_mixed_bdrv_rdlock   no_coroutine_fn coroutine_mixed_fn
 
 #include "block/blockjob.h"