Re: [Libguestfs] [PATCH libnbd 2/9] generator: Generalize OFlags.

Eric Blake
2019-08-10T17:22:44Z

On 8/10/19 8:02 AM, Richard W.M. Jones wrote:
> In a future commit we want to add (non-optional) Flags arg.  As a step
> to doing this, generalize OFlags so it's not tied to just
> NBD_CMD_FLAG_*.
>
> This does not change the C API.
>
> It does introduce a small change to the OCaml API -- putting related
> flags into a submodule, basically renaming them.  Note we don't
> provide guarantees for non-C APIs.

And even if we decide to provide guarantees for non-C, we're not at 1.0
yet ;)


> @@ -1387,7 +1403,7 @@ Returns the size in bytes of the NBD export."
>    "pread", {
>      default_call with
>      args = [ BytesOut ("buf", "count"); UInt64
"offset" ];
> -    optargs = [ OFlags "flags" ];
> +    optargs = [ OFlags ("flags", cmd_flags) ];

Do we want to use this as a chance to document which flags a given API
supports?  For example, pread supports DF but not FUA, REQ_ONE, or
MAY_TRIM.  Then again, there's still a dynamic element - the API
supports the DF flag for compilation, but the server must also support
it (nbd_can_df) before you can use it.  So any further restrictions we
decide to encode in the generator rather (or in addition) to
restrictions in lib/rw.c can be a later patch.

> +++ b/ocaml/tests/test_405_pread_structured.ml
> @@ -54,11 +54,13 @@ let () >    NBD.pread_structured nbd buf 0_L (f 42);
>    assert (buf = expected);
>
> -  NBD.pread_structured nbd buf 0_L (f 42) ~flags:[NBD.cmd_flag_df];
> +  let flags = let open NBD.CMD_FLAG in [DF] in
> +
> +  NBD.pread_structured nbd buf 0_L (f 42) ~flags;

blank line here...


> +++ b/ocaml/tests/test_410_pwrite.ml
> @@ -33,7 +33,8 @@ let () >    let nbd = NBD.create () in
>    NBD.connect_command nbd ["nbdkit"; "-s";
"--exit-with-parent"; "-v";
>                             "file"; datafile];
> -  NBD.pwrite nbd buf1 0_L ~flags:[NBD.cmd_flag_fua];
> +  let flags = let open NBD.CMD_FLAG in [FUA] in
> +  NBD.pwrite nbd buf1 0_L ~flags;

...but not here. It doesn't affect the code, but the consistency may be
worth it.

This and patch 1 look fine to me.

--
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org