Re: [PATCH-for-5.1 v3 02/24] scripts/coccinelle: Script to simplify DeviceClass error propagation

[Markus Armbruster]

Philippe Mathieu-Daudé <address@hidden> writes:

> When a device uses an Error* with data not modified before realize(),
> this call can be moved to init(). Add a Coccinelle patch to find such
> uses.
>
> Signed-off-by: Philippe Mathieu-Daudé <address@hidden>
> ---
>  ...implify-init-realize-error_propagate.cocci | 69 +++++++++++++++++++
>  MAINTAINERS                                   |  1 +
>  2 files changed, 70 insertions(+)
>  create mode 100644 
> scripts/coccinelle/simplify-init-realize-error_propagate.cocci
>
> diff --git a/scripts/coccinelle/simplify-init-realize-error_propagate.cocci 
> b/scripts/coccinelle/simplify-init-realize-error_propagate.cocci
> new file mode 100644
> index 0000000000..2e3ec4d98a
> --- /dev/null
> +++ b/scripts/coccinelle/simplify-init-realize-error_propagate.cocci
> @@ -0,0 +1,69 @@
> +// Find error-propagation calls that don't need to be in 
> DeviceClass::realize()
> +// because they don't use information user can change before calling 
> realize(),
> +// so they can be moved to DeviceClass:initfn() where error propagation is 
> not
> +// needed.
> +//
> +// Copyright: (C) 2020 Philippe Mathieu-Daudé
> +// This work is licensed under the terms of the GNU GPLv2 or later.
> +//
> +// spatch \
> +//  --macro-file scripts/cocci-macro-file.h \
> +//  --sp-file \
> +//    scripts/coccinelle/simplify-init-realize-error_propagate.cocci \
> +//  --timeout 60
> +//
> +// Inspired by https://www.mail-archive.com/address@hidden/msg692500.html
> +
> +
> +@ match_class_init @
> +TypeInfo info;
> +identifier class_initfn;
> +@@
> +    info.class_init = class_initfn;
> +
> +
> +@ match_instance_init @
> +TypeInfo info;
> +identifier instance_initfn;
> +@@
> +    info.instance_init = instance_initfn;
> +
> +
> +@ match_realize @
> +identifier match_class_init.class_initfn;
> +DeviceClass *dc;
> +identifier realizefn;
> +@@
> +void class_initfn(...)
> +{
> +    ...
> +    dc->realize = realizefn;
> +    ...
> +}

I'm afraid this misses realize() methods of DeviceClass subclasses.
Consider PCI device "i6300esb" (picked just because it's simple).

pci_device_class_init() sets DeviceClass method realize() to
pci_qdev_realize().  pci_qdev_realize() does the work common to all PCI
devices, and calls PCIDeviceClass method realize() for the work specific
to the PCI device at hand.

i6300esb_class_init() sets PCIDeviceClass method realize() to
i6300esb_realize().

Your first rule should match i6300esb_info alright, and thus identify
i6300esb_class_init() as a class_init() method.

But your third rule can't match i6300esb_class_init()'s

    k->realize = i6300esb_realize;

because @k is a PCIDeviceClass, not a DeviceClass.

I think it also misses cases that have a realize(), but no
instance_init().

Finding only some instances of an anti-pattern can still be useful.  But
you should explain the script's limitations then, both in the script and
the commit message.

> +
> +
> +@ propagate_in_realize @
> +identifier match_realize.realizefn;
> +identifier err;
> +identifier errp;
> +identifier func_with_errp =~ "(?!object_property_set_link)";

What are you trying to accomplish with this lookahead assertion?

> +symbol error_abort, error_fatal;
> +position pos;
> +@@
> +void realizefn@pos(..., Error **errp)
> +{
> +    ...
> +    Error *err = NULL;

Why is this line required for a match?

> +    <+...
> +    func_with_errp(..., \(&error_abort\|&error_fatal\));
> +    ...+>
> +}
> +
> +
> +@ script:python @
> +initfn << match_instance_init.instance_initfn;
> +realizefn << match_realize.realizefn;
> +p << propagate_in_realize.pos;
> +@@
> +print('>>> possible moves from {}() to {}() in {}:{}'
> +      .format(initfn, realizefn, p[0].file, p[0].line))
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 642c8e0b6b..6203543ec0 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -2058,6 +2058,7 @@ F: scripts/coccinelle/err-bad-newline.cocci
>  F: scripts/coccinelle/error-use-after-free.cocci
>  F: scripts/coccinelle/error_propagate_null.cocci
>  F: scripts/coccinelle/remove_local_err.cocci
> +F: scripts/coccinelle/simplify-init-realize-error_propagate.cocci
>  F: scripts/coccinelle/use-error_fatal.cocci
>  
>  GDB stub