[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [Qemu-block] [RFC PATCH v2 13/18] oslib-posix: Ignore fcntl("/dev/nu
From: |
Philippe Mathieu-Daudé |
Subject: |
Re: [Qemu-block] [RFC PATCH v2 13/18] oslib-posix: Ignore fcntl("/dev/null", F_SETFL, O_NONBLOCK) failure |
Date: |
Tue, 5 Feb 2019 14:43:39 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.4.0 |
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
>