Dominique Martinet wrote on Thu, Jun 10, 2021 at 05:33:34PM +0900: > Stefan Hajnoczi wrote on Thu, Jun 10, 2021 at 09:16:38AM +0100: > > virtio-9p should be simple. I'm not sure how much additional setup the > > other 9p transports require. TCP and RDMA seem doable if there are > > kernel parameters to configure things before the root file system is > > mounted. > > For TCP, we can probably piggyback on what nfs does for this, see the > ip= parameter in Documentation/admin-guide/nfs/nfsroot.rst -- it lives > in net/ipv4/ipconfig.c so should just work out of the box Hm, just tried and it doesn't quite work for some reason -- in this stack trace: kthread_should_stop+0x71/0xb0 wait_woken+0x182/0x1c0 __inet_stream_connect+0x48a/0xc00 inet_stream_connect+0x53/0xa0 p9_fd_create_tcp+0x2d6/0x420 p9_client_create+0x7bc/0x11d0 v9fs_session_init+0x1cd/0x1220 v9fs_mount+0x8c/0x870 legacy_get_tree+0xef/0x1d0 vfs_get_tree+0x83/0x240 path_mount+0xda3/0x1800 init_mount+0x98/0xdd do_mount_root+0xe0/0x255 mount_root+0x47/0xd7 prepare_namespace+0x136/0x165 kernel_init+0xd/0x123 ret_from_fork+0x22/0x30 current->set_child_tid is null, causing a null deref when checking &to_kthread(current)->flags It does work with nfsroot though so even if this doesn't look 9p specific I guess I'll need to debug that eventually, but this can be done later... I'm guessing they don't use the same connect() function as 9p's is ipv4-specific (ugh) and that needs fixing eventually anyway. For reference this is relevant part of kernel command line I used for tcp: root=fstag:x.y.z.t rootflags=trans=tcp,aname=rootfs rootfstype=9p ip=dhcp (and ip=dhcp requires CONFIG_IP_PNP_DHCP=y) Virtio does work quite well though and that's good enough for me -- I was going to suggest also documenting increasing the msize (setting e.g. rootflags=msize=262144) but we really ought to increase the default, that came up recently and since no patch was sent I kind of forgot... Will do that now. @Vivek - I personally don't really care much, but would tend to prefer your v2 (without fstag:) from a user perspective the later is definitely better but I don't really like the static nobdev_filesystems array -- I'd bite the bullet and use FS_REQUIRES_DEV (and move this part of the code just a bit below after the root_wait check just in case it matters, but at that point if something would mount with /dev/root but not with the raw root=argument then they probably do require a device!) It could also be gated by a config option like e.g. CONFIG_ROOT_NFS and others all are to make sure it doesn't impact anyone who doesn't want to be impacted - I'm sure some people want to make sure their device doesn't boot off a weird root if someone manages to change kernel params so would want a way of disabling the option... Well, if you keep the array, please add 9p to the list and resend as a proper patch so I can reply with tested-by/reviewed-by tags on something more final. Also, matter-of-factedly, how is this going to be picked up? Is the plan to send it directly to Linus as part of the next virtiofs PR? Going through Al Viro? Thanks, -- Dominique
