Jitendra Patidar 361a7e8211 log xattr=sa create/remove/update to ZIL ... As such, there are no specific synchronous semantics defined for the xattrs. But for xattr=on, it does log to ZIL and zil_commit() is done, if sync=always is set on dataset. This provides sync semantics for xattr=on with sync=always set on dataset. For the xattr=sa implementation, it doesn't log to ZIL, so, even with sync=always, xattrs are not guaranteed to be synced before xattr call returns to caller. So, xattr can be lost if system crash happens, before txg carrying xattr transaction is synced. This change adds xattr=sa logging to ZIL on xattr create/remove/update and xattrs are synced to ZIL (zil_commit() done) for sync=always. This makes xattr=sa behavior similar to xattr=on. Implementation notes: The actual logging is fairly straight-forward and does not warrant additional explanation. However, it has been 14 years since we last added new TX types to the ZIL [1], hence this is the first time we do it after the introduction of zpool features. Therefore, here is an overview of the feature activation and deactivation workflow: 1. The feature must be enabled. Otherwise, we don't log the new record type. This ensures compatibility with older software. 2. The feature is activated per-dataset, since the ZIL is per-dataset. 3. If the feature is enabled and dataset is not for zvol, any append to the ZIL chain will activate the feature for the dataset. Likewise for starting a new ZIL chain. 4. A dataset that doesn't have a ZIL chain has the feature deactivated. We ensure (3) by activating on the first zil_commit() after the feature was enabled. Since activating the features requires waiting for txg sync, the first zil_commit() after enabling the feature will be slower than usual. The downside is that this is really a conservative approximation: even if we never append a 'TX_SETSAXATTR' to the ZIL chain, we pay the penalty for feature activation. The upside is that the user is in control of when we pay the penalty, i.e., upon enabling the feature. We ensure (4) by hooking into zil_sync(), where ZIL destroy actually happens. One more piece on feature activation, since it's spread across multiple functions: zil_commit() zil_process_commit_list() if lwb == NULL // first zil_commit since zil_open zil_create() if no log block pointer in ZIL header: if feature enabled and not active: // CASE 1 enable, COALESCE txg wait with dmu_tx that allocated the log block else // log block was allocated earlier than this zil_open if feature enabled and not active: // CASE 2 enable, EXPLICIT txg wait else // already have an in-DRAM LWB if feature enabled and not active: // this happens when we enable the feature after zil_create // CASE 3 enable, EXPLICIT txg wait [1] da6c28aaf6 Reviewed-by: Matthew Ahrens <mahrens@delphix.com> Reviewed-by: Christian Schwarz <christian.schwarz@nutanix.com> Reviewed-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz> Reviewed-by: Ryan Moeller <freqlabs@FreeBSD.org> Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov> Signed-off-by: Jitendra Patidar <jitendra.patidar@nutanix.com> Closes #8768 Closes #9078		2022-02-22 13:06:43 -08:00
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freebsd	log xattr=sa create/remove/update to ZIL	2022-02-22 13:06:43 -08:00
linux	log xattr=sa create/remove/update to ZIL	2022-02-22 13:06:43 -08:00