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 <[email protected]>
Reviewed by: Matthew Ahrens <[email protected]>
Reviewed by: John Kennedy <[email protected]>
Reviewed by: Dan Kimmel <[email protected]>
Reviewed by: Brian Behlendorf <[email protected]>
Approved by: Richard Lowe <[email protected]>
Ported-by: Tim Chase <[email protected]>
Signed-off-by: Tim Chase <[email protected]>

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

5 files changed, 139 insertions, 4 deletions

diff --git a/lib/libzfs/libzfs_pool.c b/lib/libzfs/libzfs_pool.c
index ef98b25bc..e8c0cdfe4 100644
--- a/lib/libzfs/libzfs_pool.c
+++ b/lib/libzfs/libzfs_pool.c
@@ -350,6 +350,7 @@ zpool_get_prop(zpool_handle_t *zhp, zpool_prop_t prop, char *buf,
 			break;
 
 		case ZPOOL_PROP_EXPANDSZ:
+		case ZPOOL_PROP_CHECKPOINT:
 			if (intval == 0) {
 				(void) strlcpy(buf, "-", len);
 			} else if (literal) {
@@ -1380,6 +1381,48 @@ zpool_destroy(zpool_handle_t *zhp, const char *log_str)
 }
 
 /*
+ * Create a checkpoint in the given pool.
+ */
+int
+zpool_checkpoint(zpool_handle_t *zhp)
+{
+	libzfs_handle_t *hdl = zhp->zpool_hdl;
+	char msg[1024];
+	int error;
+
+	error = lzc_pool_checkpoint(zhp->zpool_name);
+	if (error != 0) {
+		(void) snprintf(msg, sizeof (msg), dgettext(TEXT_DOMAIN,
+		    "cannot checkpoint '%s'"), zhp->zpool_name);
+		(void) zpool_standard_error(hdl, error, msg);
+		return (-1);
+	}
+
+	return (0);
+}
+
+/*
+ * Discard the checkpoint from the given pool.
+ */
+int
+zpool_discard_checkpoint(zpool_handle_t *zhp)
+{
+	libzfs_handle_t *hdl = zhp->zpool_hdl;
+	char msg[1024];
+	int error;
+
+	error = lzc_pool_checkpoint_discard(zhp->zpool_name);
+	if (error != 0) {
+		(void) snprintf(msg, sizeof (msg), dgettext(TEXT_DOMAIN,
+		    "cannot discard checkpoint in '%s'"), zhp->zpool_name);
+		(void) zpool_standard_error(hdl, error, msg);
+		return (-1);
+	}
+
+	return (0);
+}
+
+/*
  * Add the given vdevs to the pool.  The caller must have already performed the
  * necessary verification to ensure that the vdev specification is well-formed.
  */
diff --git a/lib/libzfs/libzfs_util.c b/lib/libzfs/libzfs_util.c
index 855c72fab..a19b34415 100644
--- a/lib/libzfs/libzfs_util.c
+++ b/lib/libzfs/libzfs_util.c
@@ -22,7 +22,7 @@
 /*
  * Copyright (c) 2005, 2010, Oracle and/or its affiliates. All rights reserved.
  * Copyright (c) 2018, Joyent, Inc. All rights reserved.
- * Copyright (c) 2011, 2014 by Delphix. All rights reserved.
+ * Copyright (c) 2011, 2017 by Delphix. All rights reserved.
  * Copyright 2016 Igor Kozhukhov <[email protected]>
  * Copyright (c) 2017 Datto Inc.
  */
@@ -264,6 +264,17 @@ libzfs_error_description(libzfs_handle_t *hdl)
 	case EZFS_NO_PENDING:
 		return (dgettext(TEXT_DOMAIN, "operation is not "
 		    "in progress"));
+	case EZFS_CHECKPOINT_EXISTS:
+		return (dgettext(TEXT_DOMAIN, "checkpoint exists"));
+	case EZFS_DISCARDING_CHECKPOINT:
+		return (dgettext(TEXT_DOMAIN, "currently discarding "
+		    "checkpoint"));
+	case EZFS_NO_CHECKPOINT:
+		return (dgettext(TEXT_DOMAIN, "checkpoint does not exist"));
+	case EZFS_DEVRM_IN_PROGRESS:
+		return (dgettext(TEXT_DOMAIN, "device removal in progress"));
+	case EZFS_VDEV_TOO_BIG:
+		return (dgettext(TEXT_DOMAIN, "device exceeds supported size"));
 	case EZFS_ACTIVE_POOL:
 		return (dgettext(TEXT_DOMAIN, "pool is imported on a "
 		    "different host"));
@@ -530,7 +541,21 @@ zpool_standard_error_fmt(libzfs_handle_t *hdl, int error, const char *fmt, ...)
 	case EREMOTEIO:
 		zfs_verror(hdl, EZFS_ACTIVE_POOL, fmt, ap);
 		break;
-
+	case ZFS_ERR_CHECKPOINT_EXISTS:
+		zfs_verror(hdl, EZFS_CHECKPOINT_EXISTS, fmt, ap);
+		break;
+	case ZFS_ERR_DISCARDING_CHECKPOINT:
+		zfs_verror(hdl, EZFS_DISCARDING_CHECKPOINT, fmt, ap);
+		break;
+	case ZFS_ERR_NO_CHECKPOINT:
+		zfs_verror(hdl, EZFS_NO_CHECKPOINT, fmt, ap);
+		break;
+	case ZFS_ERR_DEVRM_IN_PROGRESS:
+		zfs_verror(hdl, EZFS_DEVRM_IN_PROGRESS, fmt, ap);
+		break;
+	case ZFS_ERR_VDEV_TOO_BIG:
+		zfs_verror(hdl, EZFS_VDEV_TOO_BIG, fmt, ap);
+		break;
 	default:
 		zfs_error_aux(hdl, strerror(error));
 		zfs_verror(hdl, EZFS_UNKNOWN, fmt, ap);
diff --git a/lib/libzfs_core/libzfs_core.c b/lib/libzfs_core/libzfs_core.c
index 5a46042a4..ab2b70519 100644
--- a/lib/libzfs_core/libzfs_core.c
+++ b/lib/libzfs_core/libzfs_core.c
@@ -1143,6 +1143,74 @@ lzc_channel_program(const char *pool, const char *program, uint64_t instrlimit,
 }
 
 /*
+ * Creates a checkpoint for the specified pool.
+ *
+ * If this function returns 0 the pool was successfully checkpointed.
+ *
+ * This method may also return:
+ *
+ * ZFS_ERR_CHECKPOINT_EXISTS
+ *	The pool already has a checkpoint. A pools can only have one
+ *	checkpoint at most, at any given time.
+ *
+ * ZFS_ERR_DISCARDING_CHECKPOINT
+ * 	ZFS is in the middle of discarding a checkpoint for this pool.
+ * 	The pool can be checkpointed again once the discard is done.
+ *
+ * ZFS_DEVRM_IN_PROGRESS
+ * 	A vdev is currently being removed. The pool cannot be
+ * 	checkpointed until the device removal is done.
+ *
+ * ZFS_VDEV_TOO_BIG
+ * 	One or more top-level vdevs exceed the maximum vdev size
+ * 	supported for this feature.
+ */
+int
+lzc_pool_checkpoint(const char *pool)
+{
+	int error;
+
+	nvlist_t *result = NULL;
+	nvlist_t *args = fnvlist_alloc();
+
+	error = lzc_ioctl(ZFS_IOC_POOL_CHECKPOINT, pool, args, &result);
+
+	fnvlist_free(args);
+	fnvlist_free(result);
+
+	return (error);
+}
+
+/*
+ * Discard the checkpoint from the specified pool.
+ *
+ * If this function returns 0 the checkpoint was successfully discarded.
+ *
+ * This method may also return:
+ *
+ * ZFS_ERR_NO_CHECKPOINT
+ * 	The pool does not have a checkpoint.
+ *
+ * ZFS_ERR_DISCARDING_CHECKPOINT
+ * 	ZFS is already in the middle of discarding the checkpoint.
+ */
+int
+lzc_pool_checkpoint_discard(const char *pool)
+{
+	int error;
+
+	nvlist_t *result = NULL;
+	nvlist_t *args = fnvlist_alloc();
+
+	error = lzc_ioctl(ZFS_IOC_POOL_DISCARD_CHECKPOINT, pool, args, &result);
+
+	fnvlist_free(args);
+	fnvlist_free(result);
+
+	return (error);
+}
+
+/*
  * Executes a read-only channel program.
  *
  * A read-only channel program works programmatically the same way as a
diff --git a/lib/libzpool/Makefile.am b/lib/libzpool/Makefile.am
index f2a7a00a8..58e3b6eec 100644
--- a/lib/libzpool/Makefile.am
+++ b/lib/libzpool/Makefile.am
@@ -92,6 +92,7 @@ KERNEL_C = \
 	skein_zfs.c \
 	spa.c \
 	spa_boot.c \
+	spa_checkpoint.c \
 	spa_config.c \
 	spa_errlog.c \
 	spa_history.c \
diff --git a/lib/libzpool/kernel.c b/lib/libzpool/kernel.c
index 1eaa51b9f..341548ac3 100644
--- a/lib/libzpool/kernel.c
+++ b/lib/libzpool/kernel.c
@@ -497,8 +497,6 @@ vn_open(char *path, int x1, int flags, int mode, vnode_t **vpp, int x2, int x3)
 #ifdef __linux__
 		flags |= O_DIRECT;
 #endif
-		/* We shouldn't be writing to block devices in userspace */
-		VERIFY(!(flags & FWRITE));
 	}
 
 	if (flags & FCREAT)