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Implement workaround for pools affected by openzfs#2094 erratum
ZoL commit 1421c89 unintentionally changed the disk format in a forward-compatible, but not backward compatible way. This was accomplished by adding an entry to zbookmark_t, which is included in a couple of on-disk structures. That lead to the creation of pools with incorrect dsl_scan_phys_t objects that could only be imported by versions of ZFSOnLinux containing that commit. Such pools cannot be imported by other versions of ZFS. That includes past and future versions of ZoL. The additional field has been removed by a prior patch. This patch permits affected pools to be imported and repaired by implementing a workaround for the erratum. When this workaround is triggered, a kernel alert describing this will be printed to dmesg asking the system administrator to run a scrub. A subsequent scrub will replace the damaged dsl_scan_phys_t object, repairing the pool. Pools affected by the damaged dsl_scan_phys_t can be detected prior to an upgrade by running the following command as root: zdb -dddd poolname 1 | grep -P '^\t\tscan = ' | sed -e 's;scan = ;;' | wc -w Note that `poolname` must be replaced with the name of the pool you wish to check. A value of 25 indicates the dsl_scan_phys_t has been damaged. A value of 24 indicates that the dsl_scan_phys_t is normal. A value of 0 indicates that there has never been a scrub run on the pool. The regression caused by the change to zbookmark_t never made it into a tagged release or any Gentoo backports. Only those using HEAD were affected. However, this patch has a few limitations. There is no way to detect a damaged dsl_scan_phys_t object when it has occurred on 32-bit systems due to integer rounding that wrote incorrect information, but avoided the overflow on them. Correcting such issues requires triggering a scrub. In addition, bptree_entry_phys_t objects are also affected. These objects only exist during an asynchronous destroy and automating repair of damaged bptree_entry_phys_t objects is non-trivial. Any pools that have been imported by an affected version of ZoL must have all asynchronous destroy operations finish before export and subsequent import by a version containing this commit. Failure to do that will prevent pool import. The presence of any background destroys on any imported pools can be checked by running `zpool get freeing` as root. This will display a non-zero value for any pool with an active asynchronous destroy. Lastly, it is expected that no user data has been lost as a result of this erratum. Closes openzfs#2094 Original-patch-by: Tim Chase <[email protected]> Signed-off-by: Richard Yao <[email protected]>
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This came up in IRC but avoid the printk. It's not defined in userspace so this completely breaks the build. Use cmn_err() or zfs_dbgmsg().