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

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

On 4/14/20 2:24 PM, Markus Armbruster wrote:
> Philippe Mathieu-Daudé <f4bug@amsat.org> 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 <f4bug@amsat.org>
>> ---
>>   ...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/qemu-devel@nongnu.org/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.

OK.

> 
>> +
>> +
>> +@ 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?

"match all func_with_errp() except object_property_set_link()"?

> 
>> +symbol error_abort, error_fatal;
>> +position pos;
>> +@@
>> +void realizefn@pos(..., Error **errp)
>> +{
>> +    ...
>> +    Error *err = NULL;
> 
> Why is this line required for a match?

Hmmm maybe I was expecting a local_err... else a left-over from previous 
intents :)

> 
>> +    <+...
>> +    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
>