linux-kernel - Re: [PATCH v11 33/46] KVM: selftests: Hyper-V PV IPI selftest

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Message-ID: <874jvxcnyp.fsf@ovpn-192-65.brq.redhat.com>
Date:   Fri, 21 Oct 2022 15:20:46 +0200
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     kvm@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Michael Kelley <mikelley@...rosoft.com>,
        Siddharth Chandrasekaran <sidcha@...zon.de>,
        Yuan Yao <yuan.yao@...ux.intel.com>,
        Maxim Levitsky <mlevitsk@...hat.com>,
        linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v11 33/46] KVM: selftests: Hyper-V PV IPI selftest

Sean Christopherson <seanjc@...gle.com> writes:

> On Tue, Oct 04, 2022, Vitaly Kuznetsov wrote:

...

>> +
>> +	r = pthread_cancel(thread);
>> +	TEST_ASSERT(r == 0,
>
> !r is generally preferred over "r == 0"
>
>> +		    "pthread_cancel on vcpu_id=%d failed with errno=%d",
>> +		    vcpu->id, r);
>
> Do you happen to know if errno is preserved?  I.e. if TEST_ASSERT()'s print of
> errno will capture the right errno?  If so, this and the pthread_join() assert
> can be:
>
> 	TEST_ASSERT(!r, pthread_cancel() failed on vcpu_id=%d, vcpu->id);
>

The example from 'man 3 pthread_cancel' makes me think errno is not
set. 'man 3 errno' confirms that:

"
       Note  that the POSIX threads APIs do not set errno on error.
Instead, on failure they return an error number as the function result.
These error numbers have the same meanings as the error numbers returned
in errno by other APIs.
"

but nothing stops us from doing something like

#include <errno.h>
...

errno = pthread_cancel(thread);
TEST_ASSERT(!errno, pthread_cancel() failed on vcpu_id=%d, vcpu->id);

I believe.

-- 
Vitaly