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Re: [PATCH v5 1/2] kvm: replace fprintf with error_report()/printf() in


From: Ani Sinha
Subject: Re: [PATCH v5 1/2] kvm: replace fprintf with error_report()/printf() in kvm_init()
Date: Wed, 28 Aug 2024 18:10:24 +0530


> On 28 Aug 2024, at 4:53 PM, Markus Armbruster <armbru@redhat.com> wrote:
> 
> Ani Sinha <anisinha@redhat.com> writes:
> 
>> error_report() is more appropriate for error situations. Replace fprintf with
>> error_report() and error_printf() as appropriate. Cosmetic. No functional
>> change.
> 
> Uh, I missed this last time around: the change is more than just
> cosmetics!  The error messages change, e.g. from
> 
>    $ qemu-system-x86_64 -nodefaults -S -display none --accel kvm
>    qemu-system-x86_64: --accel kvm: Could not access KVM kernel module: 
> Permission denied
>    qemu-system-x86_64: --accel kvm: failed to initialize kvm: Permission 
> denied
> 
> to
> 
>    $ qemu-system-x86_64 -nodefaults -S -display none --accel kvm
>    Could not access KVM kernel module: Permission denied
>    qemu-system-x86_64: --accel kvm: failed to initialize kvm: Permission 
> denied

You got this backwards. This is what I have:

Before:
$ ./qemu-system-x86_64 --accel kvm
Could not access KVM kernel module: No such file or directory
qemu-system-x86_64: --accel kvm: failed to initialize kvm: No such file or 
directory

Now:
$ ./qemu-system-x86_64 --accel kvm
qemu-system-x86_64: --accel kvm: Could not access KVM kernel module: No such 
file or directory
qemu-system-x86_64: --accel kvm: failed to initialize kvm: No such file or 
directory


> 
> Note: the second message is from kvm_init()'s caller.  Reporting the
> same error twice is wrong, but not this patch's problem.
> 
> Moreover, the patch tweaks an error message at [*].
> 
> Suggest something like
> 
>  Replace fprintf() with error_report() and error_printf() where
>  appropriate.  Error messages improve, e.g. from
> 
>      Could not access KVM kernel module: Permission denied
> 
>  to
> 
>      qemu-system-x86_64: --accel kvm: Could not access KVM kernel module: 
> Permission denied

Yes this seems correct.

> 
>> CC: qemu-trivial@nongnu.org
>> CC: zhao1.liu@intel.com
>> CC: armbru@redhat.com
>> Reviewed-by: Zhao Liu <zhao1.liu@intel.com>
>> Signed-off-by: Ani Sinha <anisinha@redhat.com>
>> ---
>> accel/kvm/kvm-all.c | 40 ++++++++++++++++++----------------------
>> 1 file changed, 18 insertions(+), 22 deletions(-)
>> 
>> changelog:
>> v2: fix a bug.
>> v3: replace one instance of error_report() with error_printf(). added tags.
>> v4: changes suggested by Markus.
>> v5: more changes from Markus's comments on v4.
>> 
>> diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
>> index 75d11a07b2..fcc157f0e6 100644
>> --- a/accel/kvm/kvm-all.c
>> +++ b/accel/kvm/kvm-all.c
>> @@ -2427,7 +2427,7 @@ static int kvm_init(MachineState *ms)
>>     QLIST_INIT(&s->kvm_parked_vcpus);
>>     s->fd = qemu_open_old(s->device ?: "/dev/kvm", O_RDWR);
>>     if (s->fd == -1) {
>> -        fprintf(stderr, "Could not access KVM kernel module: %m\n");
>> +        error_report("Could not access KVM kernel module: %m");
>>         ret = -errno;
>>         goto err;
>>     }
>> @@ -2437,13 +2437,13 @@ static int kvm_init(MachineState *ms)
>>         if (ret >= 0) {
>>             ret = -EINVAL;
>>         }
>> -        fprintf(stderr, "kvm version too old\n");
>> +        error_report("kvm version too old");
>>         goto err;
>>     }
>> 
>>     if (ret > KVM_API_VERSION) {
>>         ret = -EINVAL;
>> -        fprintf(stderr, "kvm version not supported\n");
>> +        error_report("kvm version not supported");
>>         goto err;
>>     }
>> 
>> @@ -2488,26 +2488,22 @@ static int kvm_init(MachineState *ms)
>>     } while (ret == -EINTR);
>> 
>>     if (ret < 0) {
>> -        fprintf(stderr, "ioctl(KVM_CREATE_VM) failed: %d %s\n", -ret,
>> -                strerror(-ret));
>> +        error_report("ioctl(KVM_CREATE_VM) failed: %s", strerror(-ret));
> 
> [*] This is where you change an error message.
> 
>> 
>> #ifdef TARGET_S390X
>>         if (ret == -EINVAL) {
>> -            fprintf(stderr,
>> -                    "Host kernel setup problem detected. Please verify:\n");
>> -            fprintf(stderr, "- for kernels supporting the switch_amode or"
>> -                    " user_mode parameters, whether\n");
>> -            fprintf(stderr,
>> -                    "  user space is running in primary address space\n");
>> -            fprintf(stderr,
>> -                    "- for kernels supporting the vm.allocate_pgste sysctl, 
>> "
>> -                    "whether it is enabled\n");
>> +            error_printf("Host kernel setup problem detected."
>> +                         " Please verify:\n");
>> +            error_printf("- for kernels supporting the"
>> +                        " switch_amode or user_mode parameters, whether");
>> +            error_printf(" user space is running in primary address 
>> space\n");
>> +            error_printf("- for kernels supporting the vm.allocate_pgste"
>> +                         " sysctl, whether it is enabled\n");
>>         }
>> #elif defined(TARGET_PPC)
>>         if (ret == -EINVAL) {
>> -            fprintf(stderr,
>> -                    "PPC KVM module is not loaded. Try modprobe kvm_%s.\n",
>> -                    (type == 2) ? "pr" : "hv");
>> +            error_printf("PPC KVM module is not loaded. Try modprobe 
>> kvm_%s.\n",
>> +                         (type == 2) ? "pr" : "hv");
>>         }
>> #endif
>>         goto err;
>> @@ -2526,9 +2522,9 @@ static int kvm_init(MachineState *ms)
>>                         nc->name, nc->num, soft_vcpus_limit);
>> 
>>             if (nc->num > hard_vcpus_limit) {
>> -                fprintf(stderr, "Number of %s cpus requested (%d) exceeds "
>> -                        "the maximum cpus supported by KVM (%d)\n",
>> -                        nc->name, nc->num, hard_vcpus_limit);
>> +                error_report("Number of %s cpus requested (%d) exceeds "
>> +                             "the maximum cpus supported by KVM (%d)",
>> +                             nc->name, nc->num, hard_vcpus_limit);
>>                 exit(1);
>>             }
>>         }
>> @@ -2542,8 +2538,8 @@ static int kvm_init(MachineState *ms)
>>     }
>>     if (missing_cap) {
>>         ret = -EINVAL;
>> -        fprintf(stderr, "kvm does not support %s\n%s",
>> -                missing_cap->name, upgrade_note);
>> +        error_report("kvm does not support %s", missing_cap->name);
>> +        error_printf("%s", upgrade_note);
>>         goto err;
>>     }
> 
> With the commit message corrected:
> Reviewed-by: Markus Armbruster <armbru@redhat.com>





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