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[88.187.86.199]) by smtp.gmail.com with ESMTPSA id af79cd13be357-7c958ea0b9bsm829861985a.91.2025.04.30.01.40.37 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 30 Apr 2025 01:40:38 -0700 (PDT) Message-ID: Date: Wed, 30 Apr 2025 10:40:36 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] tests/qtest/libqos: Avoid double swapping when using modern virtio To: Thomas Huth , Fabiano Rosas , qemu-devel@nongnu.org Cc: Laurent Vivier , Paolo Bonzini , Pierrick Bouvier References: <20250430073343.526867-1-thuth@redhat.com> Content-Language: en-US From: =?UTF-8?Q?Philippe_Mathieu-Daud=C3=A9?= In-Reply-To: <20250430073343.526867-1-thuth@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=2607:f8b0:4864:20::732; envelope-from=philmd@linaro.org; helo=mail-qk1-x732.google.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On 30/4/25 09:33, Thomas Huth wrote: > From: Thomas Huth > > The logic in the qvirtio_read/write function is rather a headache, > involving byte-swapping when the target is big endian, just to > maybe involve another byte-swapping in the qtest_read/write > function immediately afterwards (on the QEMU side). Let's do it in > a more obvious way here: For virtio 1.0, we know that the values have > to be little endian, so let's read/write the bytes in that well known > order here. Thanks for looking at this! > > Signed-off-by: Thomas Huth > --- > This also decreases our usage of qtest_big_endian() which might (or > might not) get helpful for the universal binary one day... > > tests/qtest/libqos/virtio.c | 61 ++++++++++++++++++++++++++----------- > 1 file changed, 44 insertions(+), 17 deletions(-) > > diff --git a/tests/qtest/libqos/virtio.c b/tests/qtest/libqos/virtio.c > index 2e7979652fd..078adf3c8dc 100644 > --- a/tests/qtest/libqos/virtio.c > +++ b/tests/qtest/libqos/virtio.c > @@ -25,49 +25,76 @@ > */ > static uint16_t qvirtio_readw(QVirtioDevice *d, QTestState *qts, uint64_t addr) > { > - uint16_t val = qtest_readw(qts, addr); > + uint8_t buf[2]; > > - if (d->features & (1ull << VIRTIO_F_VERSION_1) && qtest_big_endian(qts)) { > - val = bswap16(val); > + if (d->features & (1ull << VIRTIO_F_VERSION_1)) { > + qtest_memread(qts, addr, buf, sizeof(buf)); > + return (buf[1] << 8) | buf[0]; > + } else { > + return qtest_readw(qts, addr); > } > - return val; > } What about using cpu_to_le() API? -- >8 -- static uint16_t qvirtio_readw(QVirtioDevice *d, QTestState *qts, uint64_t addr) { - uint16_t val = qtest_readw(qts, addr); + uint16_t val; - if (d->features & (1ull << VIRTIO_F_VERSION_1) && qtest_big_endian(qts)) { - val = bswap16(val); + if (d->features & (1ull << VIRTIO_F_VERSION_1)) { + qtest_memread(qts, addr, &val, sizeof(val)); + cpu_to_le16s(&val); + } else { + val = qtest_readw(qts, addr); } + return val; } ---