OpenZFS 9166 - zfs storage pool checkpoint

Details about the motivation of this feature and its usage can
be found in this blogpost:

    https://sdimitro.github.io/post/zpool-checkpoint/

A lightning talk of this feature can be found here:
https://www.youtube.com/watch?v=fPQA8K40jAM

Implementation details can be found in big block comment of
spa_checkpoint.c

Side-changes that are relevant to this commit but not explained
elsewhere:

* renames members of "struct metaslab trees to be shorter without
  losing meaning

* space_map_{alloc,truncate}() accept a block size as a
  parameter. The reason is that in the current state all space
  maps that we allocate through the DMU use a global tunable
  (space_map_blksz) which defauls to 4KB. This is ok for metaslab
  space maps in terms of bandwirdth since they are scattered all
  over the disk. But for other space maps this default is probably
  not what we want. Examples are device removal's vdev_obsolete_sm
  or vdev_chedkpoint_sm from this review. Both of these have a
  1:1 relationship with each vdev and could benefit from a bigger
  block size.

Porting notes:

* The part of dsl_scan_sync() which handles async destroys has
  been moved into the new dsl_process_async_destroys() function.

* Remove "VERIFY(!(flags & FWRITE))" in "kernel.c" so zhack can write
  to block device backed pools.

* ZTS:
  * Fix get_txg() in zpool_sync_001_pos due to "checkpoint_txg".

  * Don't use large dd block sizes on /dev/urandom under Linux in
    checkpoint_capacity.

  * Adopt Delphix-OS's setting of 4 (spa_asize_inflation =
    SPA_DVAS_PER_BP + 1) for the checkpoint_capacity test to speed
    its attempts to fill the pool

  * Create the base and nested pools with sync=disabled to speed up
    the "setup" phase.

  * Clear labels in test pool between checkpoint tests to avoid
    duplicate pool issues.

  * The import_rewind_device_replaced test has been marked as "known
    to fail" for the reasons listed in its DISCLAIMER.

  * New module parameters:

      zfs_spa_discard_memory_limit,
      zfs_remove_max_bytes_pause (not documented - debugging only)
      vdev_max_ms_count (formerly metaslabs_per_vdev)
      vdev_min_ms_count

Authored by: Serapheim Dimitropoulos <serapheim.dimitro@delphix.com>
Reviewed by: Matthew Ahrens <mahrens@delphix.com>
Reviewed by: John Kennedy <john.kennedy@delphix.com>
Reviewed by: Dan Kimmel <dan.kimmel@delphix.com>
Reviewed by: Brian Behlendorf <behlendorf1@llnl.gov>
Approved by: Richard Lowe <richlowe@richlowe.net>
Ported-by: Tim Chase <tim@chase2k.com>
Signed-off-by: Tim Chase <tim@chase2k.com>

OpenZFS-issue: https://illumos.org/issues/9166
OpenZFS-commit: https://github.com/openzfs/openzfs/commit/7159fdb8
Closes #7570

include/sys/fs/zfs.h

@@ -239,6 +239,7 @@ typedef enum {
 	ZPOOL_PROP_TNAME,
 	ZPOOL_PROP_MAXDNODESIZE,
 	ZPOOL_PROP_MULTIHOST,
+	ZPOOL_PROP_CHECKPOINT,
 	ZPOOL_NUM_PROPS
 } zpool_prop_t;
 
@@ -616,6 +617,7 @@ typedef struct zpool_load_policy {
 #define	ZPOOL_CONFIG_DTL		"DTL"
 #define	ZPOOL_CONFIG_SCAN_STATS		"scan_stats"	/* not stored on disk */
 #define	ZPOOL_CONFIG_REMOVAL_STATS	"removal_stats"	/* not stored on disk */
+#define	ZPOOL_CONFIG_CHECKPOINT_STATS	"checkpoint_stats" /* not on disk */
 #define	ZPOOL_CONFIG_VDEV_STATS		"vdev_stats"	/* not stored on disk */
 #define	ZPOOL_CONFIG_INDIRECT_SIZE	"indirect_size"	/* not stored on disk */
 
@@ -752,6 +754,8 @@ typedef struct zpool_load_policy {
 	"com.delphix:indirect_obsolete_sm"
 #define	VDEV_TOP_ZAP_OBSOLETE_COUNTS_ARE_PRECISE \
 	"com.delphix:obsolete_counts_are_precise"
+#define	VDEV_TOP_ZAP_POOL_CHECKPOINT_SM \
+	"com.delphix:pool_checkpoint_sm"
 
 /*
  * This is needed in userland to report the minimum necessary device size.
@@ -861,6 +865,18 @@ typedef enum pool_scrub_cmd {
 	POOL_SCRUB_FLAGS_END
 } pool_scrub_cmd_t;
 
+typedef enum {
+	CS_NONE,
+	CS_CHECKPOINT_EXISTS,
+	CS_CHECKPOINT_DISCARDING,
+	CS_NUM_STATES
+} checkpoint_state_t;
+
+typedef struct pool_checkpoint_stat {
+	uint64_t pcs_state;		/* checkpoint_state_t */
+	uint64_t pcs_start_time;	/* time checkpoint/discard started */
+	uint64_t pcs_space;		/* checkpointed space */
+} pool_checkpoint_stat_t;
 
 /*
  * ZIO types.  Needed to interpret vdev statistics below.
@@ -958,7 +974,7 @@ typedef struct vdev_stat {
 	uint64_t	vs_scan_removing;	/* removing?	*/
 	uint64_t	vs_scan_processed;	/* scan processed bytes	*/
 	uint64_t	vs_fragmentation;	/* device fragmentation */
-
+	uint64_t	vs_checkpoint_space;    /* checkpoint-consumed space */
 } vdev_stat_t;
 
 /*
@@ -1144,6 +1160,8 @@ typedef enum zfs_ioc {
 	ZFS_IOC_UNLOAD_KEY,
 	ZFS_IOC_CHANGE_KEY,
 	ZFS_IOC_REMAP,
+	ZFS_IOC_POOL_CHECKPOINT,
+	ZFS_IOC_POOL_DISCARD_CHECKPOINT,
 
 	/*
 	 * Linux - 3/64 numbers reserved.
@@ -1166,6 +1184,22 @@ typedef enum zfs_ioc {
  */
 #define	BLKZNAME		_IOR(0x12, 125, char[ZFS_MAX_DATASET_NAME_LEN])
 
+/*
+ * ZFS-specific error codes used for returning descriptive errors
+ * to the userland through zfs ioctls.
+ *
+ * The enum implicitly includes all the error codes from errno.h.
+ * New code should use and extend this enum for errors that are
+ * not described precisely by generic errno codes.
+ */
+typedef enum {
+	ZFS_ERR_CHECKPOINT_EXISTS = 1024,
+	ZFS_ERR_DISCARDING_CHECKPOINT,
+	ZFS_ERR_NO_CHECKPOINT,
+	ZFS_ERR_DEVRM_IN_PROGRESS,
+	ZFS_ERR_VDEV_TOO_BIG
+} zfs_errno_t;
+
 /*
  * Internal SPA load state.  Used by FMA diagnosis engine.
  */
@@ -1235,6 +1269,7 @@ typedef enum {
 #define	ZFS_IMPORT_TEMP_NAME	0x10
 #define	ZFS_IMPORT_SKIP_MMP	0x20
 #define	ZFS_IMPORT_LOAD_KEYS	0x40
+#define	ZFS_IMPORT_CHECKPOINT	0x80
 
 /*
  * Channel program argument/return nvlist keys and defaults.