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[101.51.194.201]) by smtp.gmail.com with ESMTPSA id k12sm5347866pjm.52.2021.09.10.05.14.10 for (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 10 Sep 2021 05:14:12 -0700 (PDT) From: Andreas Bauer X-Google-Original-From: Andreas Bauer Date: Fri, 10 Sep 2021 19:14:07 +0700 To: linux-kernel@vger.kernel.org Subject: 9pnet_virtio missing dependency Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Dear all, While compiling a minimal qemu kernel 5.14.2 with 9p root fs, I encountered a problem with the 9pnet_virtio code: | [ 0.553249] 9pnet: Installing 9P2000 support [...] | [ 0.561547] 9pnet: -- v9fs_mount (1): | [ 0.562156] 9pnet_virtio: no channels available for device /dev/root 9p_virtio_create() is called and the list of channels in this loop | list_for_each_entry(chan, &virtio_chan_list, chan_list) { turns out to be empty. After instrumenting the code with a few more debug outputs, it turns out p9_virtio_probe() is not called. I am not familiar enough with the code flow to see exactly where the problem lies. I think all relevant kernel options are enabled: | $ cat .config | grep -Ei '9P|VIRTIO' | grep -v "^#" | sort | CONFIG_9P_FS_POSIX_ACL=y | CONFIG_9P_FS_SECURITY=y | CONFIG_9P_FS=y | CONFIG_ARCH_HAS_RESTRICTED_VIRTIO_MEMORY_ACCESS=y | CONFIG_BLK_MQ_VIRTIO=y | CONFIG_HW_RANDOM_VIRTIO=y | CONFIG_NET_9P_DEBUG=y | CONFIG_NET_9P_VIRTIO=y | CONFIG_NET_9P=y | CONFIG_VIRTIO_BLK=y | CONFIG_VIRTIO_CONSOLE=y | CONFIG_VIRTIO_FS=y | CONFIG_VIRTIO_INPUT=y | CONFIG_VIRTIO_MEM=y | CONFIG_VIRTIO_MENU=y | CONFIG_VIRTIO_NET=y | CONFIG_VIRTIO_PCI_LEGACY=y | CONFIG_VIRTIO_PCI_LIB=y | CONFIG_VIRTIO_PCI=y | CONFIG_VIRTIO=y It seems that there is a dependecy on some other kernel code that is neither documented nor instrumented in config-logic. When I compile a distribution kernel (i.e. almost everything compiled in) with "localyesconfig" the 9p root fs is found and mounted properly. What code is missing? Thanks, Andreas