fs/zfs: fall back to VFS when zfs stats are unavailable#3918
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After the filesystem plugin migration, ZFS was selected whenever /dev/zfs existed. Unprivileged containers often still have that device node but cannot talk to the zfs module (EPERM), so GetStats failed and kubelet lost rootfs capacity data. Treat missing/unusable /dev/zfs and any zfs list failure as ErrFallbackToVFS so capacity is still reported via statfs, matching the pre-migration practical behavior on unprivileged hosts. Fixes google#3904 Signed-off-by: Dean Chen <862469039@qq.com>
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Description
Unprivileged containers (e.g. LXC) with a ZFS root often still have
/dev/zfs, but the process cannot use the zfs module. After the filesystem plugin migration (#3794), cAdvisor selected the ZFS plugin whenever the device node existed and returned an error fromGetZfsStatsinstead of falling back to VFS. That leaves kubelet without rootfs capacity (cannot find filesystem info for device "zfs/...").This restores the practical pre-migration behavior for those hosts:
/dev/zfsis missing or unusable, fall back to VFS viaErrFallbackToVFSzfs listfails for any reason (including EPERM), fall back to VFS as wellPrivileged hosts with working ZFS continue to use native zfs stats.
Related Issue
Fixes #3904
Testing Done
TestGetStatsFallsBackWhenDevMissingTestGetStatsFallsBackOnZfsError(simulates EPERM after device present)TestGetStatsSuccessTestParseZfsListUsage