Re: [Qemu-block] [RFC PATCH v2 13/18] oslib-posix: Ignore fcntl("/dev/null", F_SETFL, O_NONBLOCK) failure

[Philippe Mathieu-Daudé]

On 2/5/19 2:22 PM, Peter Maydell wrote:
> On Tue, 29 Jan 2019 at 17:59, Philippe Mathieu-Daudé <address@hidden> wrote:
>>
>> Previous to OpenBSD 6.3 [1], fcntl(F_SETFL) is not permitted on
>> memory devices.
>> Trying this call sets errno to ENODEV ("not a memory device"):
>>
>>   19 ENODEV Operation not supported by device.
>>     An attempt was made to apply an inappropriate function to a device,
>>     for example, trying to read a write-only device such as a printer.
>>
>> Do not assert fcntl failures in this specific case (errno set to ENODEV)
>> on OpenBSD. This fixes:
>>
>>   $ lm32-softmmu/qemu-system-lm32
>>   assertion "f != -1" failed: file "util/oslib-posix.c", line 247, function 
>> "qemu_set_nonblock"
>>   Abort trap (core dumped)
>>
>> [1] The fix seems https://github.com/openbsd/src/commit/c2a35b387f9d3c
>>   "fcntl(F_SETFL) invokes the FIONBIO and FIOASYNC ioctls internally, so
>>   the memory devices (/dev/null, /dev/zero, etc) need to permit them."
>>
>> Signed-off-by: Philippe Mathieu-Daudé <address@hidden>
>> ---
>>  util/oslib-posix.c | 10 ++++++++++
>>  1 file changed, 10 insertions(+)
>>
>> diff --git a/util/oslib-posix.c b/util/oslib-posix.c
>> index 4ce1ba9ca4..2f0f27e6d9 100644
>> --- a/util/oslib-posix.c
>> +++ b/util/oslib-posix.c
>> @@ -244,7 +244,17 @@ void qemu_set_nonblock(int fd)
>>      f = fcntl(fd, F_GETFL);
>>      assert(f != -1);
>>      f = fcntl(fd, F_SETFL, f | O_NONBLOCK);
>> +#ifdef __OpenBSD__
>> +    if (f == -1) {
>> +        /*
>> +         * Previous to OpenBSD 6.3, fcntl(F_SETFL) is not permitted on
>> +         * memory devices and sets errno to ENODEV.
>> +         */
>> +        assert(errno == ENODEV);
>> +    }
>> +#else
>>      assert(f != -1);
>> +#endif
> 
> You might also add "It's OK if we fail to set O_NONBLOCK on devices
> like /dev/null, because they will never block anyway."

OK!

> Reviewed-by: Peter Maydell <address@hidden>

Thanks for reviewing this series :)

> 
> thanks
> -- PMM
>