vminit: pre-reqs for a read-only erofs rootfs mounted via virtio-pmem#209
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vminit: pre-reqs for a read-only erofs rootfs mounted via virtio-pmem#209djs55 wants to merge 1 commit into
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When booting from a real rootfs (erofs image exposed as a virtio-pmem device) rather than a tmpfs initramfs, systemMounts needs two changes: 1. Handle EBUSY on the devtmpfs /dev mount. With a real rootfs and CONFIG_DEVTMPFS_MOUNT=y, the kernel auto-mounts devtmpfs at /dev before running init, so vminitd's own mount attempt returns EBUSY. Treat EBUSY as success — the devices are already present. With a cpio initramfs (tmpfs rootfs) /dev was never in the archive so the kernel couldn't auto-mount there and this path always did a fresh mount. The EBUSY check is a no-op in that case. 2. Add tmpfs mounts for /etc and /mnt. An erofs rootfs is read-only. vminitd writes resolv.conf to /etc and the container shim creates bind-mount target directories under /mnt. Mounting a tmpfs over each provides the writable scratch space they need. On a writable rootfs (tmpfs initramfs) these mounts are equivalent to what was already there. Signed-off-by: David Scott <dave@recoil.org>
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ah, looks like it's already being covered by #208 , I'll close! |
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I'm experimenting with switching to a read-only erofs rootfs. I hit 2 issues:
Handle EBUSY on the devtmpfs /dev mount.
With a real rootfs and CONFIG_DEVTMPFS_MOUNT=y, the kernel auto-mounts devtmpfs at /dev before running init, so vminitd's own mount attempt returns EBUSY. Treat EBUSY as success — the devices are already present.
With a cpio initramfs (tmpfs rootfs) /dev was never in the archive so the kernel couldn't auto-mount there and this path always did a fresh mount. The EBUSY check is a no-op in that case.
Add tmpfs mounts for /etc and /mnt.
An erofs rootfs is read-only. vminitd writes resolv.conf to /etc and the container shim creates bind-mount target directories under /mnt. Mounting a tmpfs over each provides the writable scratch space they need. On a writable rootfs (tmpfs initramfs) these mounts are equivalent to what was already there.