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From: "Philippe Mathieu-Daudé" <philmd@redhat.com>
To: Alexander Graf <agraf@csgraf.de>,
	Richard Henderson <richard.henderson@linaro.org>,
	Peter Maydell <peter.maydell@linaro.org>,
	Markus Armbruster <armbru@redhat.com>
Cc: Eduardo Habkost <ehabkost@redhat.com>,
	QEMU Developers <qemu-devel@nongnu.org>,
	Cameron Esfahani <dirty@apple.com>,
	Roman Bolshakov <r.bolshakov@yadro.com>,
	qemu-arm <qemu-arm@nongnu.org>, Frank Yang <lfy@google.com>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Peter Collingbourne <pcc@google.com>
Subject: Re: [PATCH v8 16/19] hvf: arm: Implement PSCI handling
Date: Mon, 13 Sep 2021 12:30:30 +0200	[thread overview]
Message-ID: <db51fd0c-42c0-19c0-2049-bb56e88c4b51@redhat.com> (raw)
In-Reply-To: <6fe284da-6989-f837-adda-1aa722f0d345@csgraf.de>

+Markus

On 9/13/21 12:06 PM, Alexander Graf wrote:
> On 12.09.21 23:40, Richard Henderson wrote:
>> On 9/12/21 2:37 PM, Alexander Graf wrote:
>>>
>>> On 12.09.21 23:20, Richard Henderson wrote:
>>>> On 9/12/21 1:36 PM, Alexander Graf wrote:
>>>>>> I think the callsites would be clearer if you made the function
>>>>>> return true for "PSCI call handled", false for "not recognised,
>>>>>> give the guest an UNDEF". Code like
>>>>>>            if (hvf_handle_psci_call(cpu)) {
>>>>>>                stuff;
>>>>>>            }
>>>>>>
>>>>>> looks like the 'stuff' is for the "psci call handled" case,
>>>>>> which at the moment it isn't.
>>>>>
>>>>>
>>>>> This function merely follows standard C semantics along the lines
>>>>> of "0
>>>>> means success, !0 is error". Isn't that what you would usually expect?
>>>>
>>>> No, not really.  I expect stuff that returns error codes to return
>>>> negative integers on failure.  I expect stuff that returns a boolean
>>>> success/failure to return true on success.
>>>
>>>
>>> Fair, I'll change it to return -1 then. Thanks!
>>
>> Not quite the point I was making.  If the only two return values are
>> -1/0, then bool false/true is in fact more appropriate.
> 
> 
> If the whole code base adheres to it, maybe. The big problem with using
> true/false as return values for functions that don't make it very
> explicit (have an is in their name or use gerund for example). QEMU uses
> a lot of 0 == success internally.
> 
> If you now add bools to the a code base that already uses int returns a
> lot, you always need to look up what a function actually returns if the
> caller treats it as bool (if, ?, assert, etc), making code review and
> reasoning about code flows extremely hard. I've had one too many
> occasions where I called an innocently looking API and put the assert()
> the wrong way around for example.
> 
> I don't think we can solve this problem here, but IMHO the only sensible
> way to get to good readability would be to have functions that return
> success/failure return a libc defined struct that indicates the error.
> Then check for success explicitly on every caller site. Overloading bool
> or int for success/failure return is just bad :).

IIUC what we are trying to do lately is, if caller only expects
success/failure then return boolean, with error information in
Error* for eventual propagation. Only return libc errno if the
caller has to handle failures differently.



  reply	other threads:[~2021-09-13 10:34 UTC|newest]

Thread overview: 66+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-19 20:22 [PATCH v8 00/19] hvf: Implement Apple Silicon Support Alexander Graf
2021-05-19 20:22 ` [PATCH v8 01/19] hvf: Move assert_hvf_ok() into common directory Alexander Graf
2021-05-27 10:00   ` Sergio Lopez
2021-05-19 20:22 ` [PATCH v8 02/19] hvf: Move vcpu thread functions " Alexander Graf
2021-05-27 10:01   ` Sergio Lopez
2021-05-19 20:22 ` [PATCH v8 03/19] hvf: Move cpu " Alexander Graf
2021-05-27 10:02   ` Sergio Lopez
2021-05-19 20:22 ` [PATCH v8 04/19] hvf: Move hvf internal definitions into common header Alexander Graf
2021-05-27 10:04   ` Sergio Lopez
2021-05-19 20:22 ` [PATCH v8 05/19] hvf: Make hvf_set_phys_mem() static Alexander Graf
2021-05-27 10:06   ` Sergio Lopez
2021-05-19 20:22 ` [PATCH v8 06/19] hvf: Remove use of hv_uvaddr_t and hv_gpaddr_t Alexander Graf
2021-05-27 10:07   ` Sergio Lopez
2021-05-19 20:22 ` [PATCH v8 07/19] hvf: Split out common code on vcpu init and destroy Alexander Graf
2021-05-27 10:09   ` Sergio Lopez
2021-05-19 20:22 ` [PATCH v8 08/19] hvf: Use cpu_synchronize_state() Alexander Graf
2021-05-27 10:15   ` Sergio Lopez
2021-05-19 20:22 ` [PATCH v8 09/19] hvf: Make synchronize functions static Alexander Graf
2021-05-27 10:15   ` Sergio Lopez
2021-05-19 20:22 ` [PATCH v8 10/19] hvf: Remove hvf-accel-ops.h Alexander Graf
2021-05-27 10:16   ` Sergio Lopez
2021-05-19 20:22 ` [PATCH v8 11/19] hvf: Introduce hvf vcpu struct Alexander Graf
2021-05-27 10:18   ` Sergio Lopez
2021-05-19 20:22 ` [PATCH v8 12/19] hvf: Simplify post reset/init/loadvm hooks Alexander Graf
2021-05-27 10:20   ` Sergio Lopez
2021-05-19 20:22 ` [PATCH v8 13/19] hvf: Add Apple Silicon support Alexander Graf
2021-05-27 10:55   ` Sergio Lopez
2021-06-15 10:21   ` Peter Maydell
2021-06-27 20:40     ` Alexander Graf
2021-05-19 20:22 ` [PATCH v8 14/19] arm/hvf: Add a WFI handler Alexander Graf
2021-05-27 10:53   ` Sergio Lopez
2021-06-15 10:38   ` Peter Maydell
2021-05-19 20:22 ` [PATCH v8 15/19] hvf: arm: Implement -cpu host Alexander Graf
2021-05-27 11:18   ` Sergio Lopez
2021-06-15 10:56   ` Peter Maydell
2021-09-12 20:23     ` Alexander Graf
2021-09-13  8:28       ` Peter Maydell
2021-09-13 10:46         ` Alexander Graf
2021-09-13 10:52           ` Peter Maydell
2021-09-13 11:46             ` Alexander Graf
2021-09-13 11:48               ` Peter Maydell
2021-09-13 11:55                 ` Alexander Graf
2021-05-19 20:22 ` [PATCH v8 16/19] hvf: arm: Implement PSCI handling Alexander Graf
2021-05-27 11:20   ` Sergio Lopez
2021-06-15 12:54   ` Peter Maydell
2021-09-12 20:36     ` Alexander Graf
2021-09-12 21:20       ` Richard Henderson
2021-09-12 21:37         ` Alexander Graf
2021-09-12 21:40           ` Richard Henderson
2021-09-13 10:06             ` Alexander Graf
2021-09-13 10:30               ` Philippe Mathieu-Daudé [this message]
2021-05-19 20:22 ` [PATCH v8 17/19] arm: Add Hypervisor.framework build target Alexander Graf
2021-05-27 11:20   ` Sergio Lopez
2021-06-15 10:59   ` Peter Maydell
2021-05-19 20:22 ` [PATCH v8 18/19] arm: Enable Windows 10 trusted SMCCC boot call Alexander Graf
2021-05-27 11:21   ` Sergio Lopez
2021-06-15 11:02   ` Peter Maydell
2021-06-27 21:12     ` Alexander Graf
2021-05-19 20:22 ` [PATCH v8 19/19] hvf: arm: Handle Windows 10 SMC call Alexander Graf
2021-05-27 11:22   ` Sergio Lopez
2021-06-15  9:31   ` Peter Maydell
2021-06-27 21:07     ` Alexander Graf
2021-05-19 20:45 ` [PATCH v8 00/19] hvf: Implement Apple Silicon Support no-reply
2021-06-03 13:43 ` Peter Maydell
2021-06-03 13:53   ` Alexander Graf
2021-06-15 12:54   ` Peter Maydell

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