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6e91a72fe3
The implementation of 'zfs remap' has proven to be problematic since it modifies the objset (but not its logical contents) by dirtying metadata without owning it. The consequence of which is that dmu_objset_remap_indirects() is vulnerable to certain races. For example, if we are in the middle of receiving into the filesystem while it is being remapped. Then it is possible we could evict the objset when the receive completes (see dsl_dataset_clone_swap_sync_impl, or dmu_recv_end_sync), but dmu_objset_remap_indirects() may be still using the objset. The result of which would be a panic. Extended runs of ztest(8) have exposed other possible races which can occur when using 'zfs remap'. Several of these have been fixed but there may be others which have not yet been encountered and diagnosed. Furthermore, the ability to manually remap a filesystem is no longer particularly useful now that the removal code can map large chunks. Coupled with the fact that explaining what this command does and why it may be useful requires a detailed understanding of the internals of device removal. These are details users should not be bothered with. Therefore, the 'zfs remap' command is being disabled but not entirely removed. It may be removed in the future or potentially reworked to address the issues described above. Since 'zfs remap' has never been part of a tagged release its removal is expected to have minimal impact. The ZTS tests have been updated to continue to exercise the command to prevent atrophy, but it has been removed entirely from ztest(8). Reviewed by: Matt Ahrens <mahrens@delphix.com> Reviewed by: Tom Caputi <tcaputi@datto.com> Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov> Closes #8238 |
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