diff --git a/kmod/src/Makefile b/kmod/src/Makefile
index 2666e6df..dde66039 100644
--- a/kmod/src/Makefile
+++ b/kmod/src/Makefile
@@ -9,6 +9,7 @@ CFLAGS_scoutfs_trace.o = -I$(src) # define_trace.h double include
  
 scoutfs-y +=			\
 	acl.o			\
+	attr_x.o		\
 	avl.o			\
 	alloc.o			\
 	block.o			\
diff --git a/kmod/src/attr_x.c b/kmod/src/attr_x.c
new file mode 100644
index 00000000..75c62b32
--- /dev/null
+++ b/kmod/src/attr_x.c
@@ -0,0 +1,218 @@
+/*
+ * Copyright (C) 2024 Versity Software, Inc.  All rights reserved.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public
+ * License v2 as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ */
+#include <linux/kernel.h>
+#include <linux/fs.h>
+
+#include "format.h"
+#include "super.h"
+#include "inode.h"
+#include "ioctl.h"
+#include "lock.h"
+#include "trans.h"
+#include "attr_x.h"
+
+static int validate_attr_x_input(struct super_block *sb, struct scoutfs_ioctl_inode_attr_x *iax)
+{
+	int ret;
+
+	if ((iax->x_mask & SCOUTFS_IOC_IAX__UNKNOWN) ||
+	    (iax->x_flags & SCOUTFS_IOC_IAX_F__UNKNOWN))
+		return -EINVAL;
+
+	return 0;
+}
+
+/*
+ * If the mask indicates interest in the given attr then set the field
+ * to the caller's value and return the new size if it didn't already
+ * include the attr field.
+ */
+#define fill_attr(size, iax, bit, field, val)							\
+({												\
+	__typeof__(iax) _iax = (iax);								\
+	__typeof__(size) _size = (size);							\
+												\
+	if (_iax->x_mask & (bit)) {								\
+		_iax->field = (val);								\
+		_size = max(_size, offsetof(struct scoutfs_ioctl_inode_attr_x, field) +		\
+				   sizeof_field(struct scoutfs_ioctl_inode_attr_x, field));	\
+	}											\
+												\
+	_size;											\
+})
+
+/*
+ * Returns -errno on error, or >= number of bytes filled by the
+ * response.  0 can be returned if no attributes are requested in the
+ * input x_mask.
+ */
+int scoutfs_get_attr_x(struct inode *inode, struct scoutfs_ioctl_inode_attr_x *iax)
+{
+	struct super_block *sb = inode->i_sb;
+	struct scoutfs_inode_info *si = SCOUTFS_I(inode);
+	struct scoutfs_lock *lock = NULL;
+	size_t size = 0;
+	u64 offline;
+	u64 online;
+	u64 bits;
+	int ret;
+
+	if (iax->x_mask == 0) {
+		ret = 0;
+		goto out;
+	}
+
+	ret = validate_attr_x_input(sb, iax);
+	if (ret < 0)
+		goto out;
+
+	inode_lock(inode);
+
+	ret = scoutfs_lock_inode(sb, SCOUTFS_LOCK_READ, SCOUTFS_LKF_REFRESH_INODE, inode, &lock);
+	if (ret)
+		goto unlock;
+
+	size = fill_attr(size, iax, SCOUTFS_IOC_IAX_META_SEQ,
+			 meta_seq, scoutfs_inode_meta_seq(inode));
+	size = fill_attr(size, iax, SCOUTFS_IOC_IAX_DATA_SEQ,
+			 data_seq, scoutfs_inode_data_seq(inode));
+	size = fill_attr(size, iax, SCOUTFS_IOC_IAX_DATA_VERSION,
+			 data_version, scoutfs_inode_data_version(inode));
+	if (iax->x_mask & (SCOUTFS_IOC_IAX_ONLINE_BLOCKS | SCOUTFS_IOC_IAX_OFFLINE_BLOCKS)) {
+		scoutfs_inode_get_onoff(inode, &online, &offline);
+		size = fill_attr(size, iax, SCOUTFS_IOC_IAX_ONLINE_BLOCKS,
+				 online_blocks, online);
+		size = fill_attr(size, iax, SCOUTFS_IOC_IAX_OFFLINE_BLOCKS,
+				 offline_blocks, offline);
+	}
+	size = fill_attr(size, iax, SCOUTFS_IOC_IAX_CTIME, ctime_sec, inode->i_ctime.tv_sec);
+	size = fill_attr(size, iax, SCOUTFS_IOC_IAX_CTIME, ctime_nsec, inode->i_ctime.tv_nsec);
+	size = fill_attr(size, iax, SCOUTFS_IOC_IAX_CRTIME, crtime_sec, si->crtime.tv_sec);
+	size = fill_attr(size, iax, SCOUTFS_IOC_IAX_CRTIME, crtime_nsec, si->crtime.tv_nsec);
+	size = fill_attr(size, iax, SCOUTFS_IOC_IAX_SIZE, size, i_size_read(inode));
+
+	ret = size;
+unlock:
+	scoutfs_unlock(sb, lock, SCOUTFS_LOCK_READ);
+	inode_unlock(inode);
+out:
+	return ret;
+}
+
+static bool valid_attr_changes(struct inode *inode, struct scoutfs_ioctl_inode_attr_x *iax)
+{
+	/* provided data_version must be non-zero */
+	if ((iax->x_mask & SCOUTFS_IOC_IAX_DATA_VERSION) && (iax->data_version == 0))
+		return false;
+
+	/* can only set size or data version in new regular files */
+	if (((iax->x_mask & SCOUTFS_IOC_IAX_SIZE) ||
+	     (iax->x_mask & SCOUTFS_IOC_IAX_DATA_VERSION)) &&
+	    (!S_ISREG(inode->i_mode) || scoutfs_inode_data_version(inode) != 0))
+		return false;
+
+	/* must provide non-zero data_version with non-zero size */
+	if (((iax->x_mask & SCOUTFS_IOC_IAX_SIZE) && (iax->size > 0)) &&
+	    (!(iax->x_mask & SCOUTFS_IOC_IAX_DATA_VERSION) || (iax->data_version == 0)))
+		return false;
+
+	/* must provide non-zero size when setting offline extents to that size */
+	if ((iax->x_flags & SCOUTFS_IOC_IAX_F_SIZE_OFFLINE) &&
+	    (!(iax->x_mask & SCOUTFS_IOC_IAX_SIZE) || (iax->size == 0)))
+		return false;
+
+	return true;
+}
+
+int scoutfs_set_attr_x(struct inode *inode, struct scoutfs_ioctl_inode_attr_x *iax)
+{
+	struct super_block *sb = inode->i_sb;
+	struct scoutfs_inode_info *si = SCOUTFS_I(inode);
+	struct scoutfs_lock *lock = NULL;
+	LIST_HEAD(ind_locks);
+	bool set_data_seq;
+	int ret;
+
+	/* initially all setting is root only, could loosen with finer grained checks */
+	if (!capable(CAP_SYS_ADMIN)) {
+		ret = -EPERM;
+		goto out;
+	}
+
+	if (iax->x_mask == 0) {
+		ret = 0;
+		goto out;
+	}
+
+	ret = validate_attr_x_input(sb, iax);
+	if (ret < 0)
+		goto out;
+
+	inode_lock(inode);
+
+	ret = scoutfs_lock_inode(sb, SCOUTFS_LOCK_WRITE, SCOUTFS_LKF_REFRESH_INODE, inode, &lock);
+	if (ret)
+		goto unlock;
+
+	/* check for errors before making any changes */
+	if (!valid_attr_changes(inode, iax)) {
+		ret = -EINVAL;
+		goto unlock;
+	}
+
+	/* setting only so we don't see 0 data seq with nonzero data_version */
+	if ((iax->x_mask & SCOUTFS_IOC_IAX_DATA_VERSION) && (iax->data_version > 0))
+		set_data_seq = true;
+	else
+		set_data_seq = false;
+
+	ret = scoutfs_inode_index_lock_hold(inode, &ind_locks, set_data_seq, true);
+	if (ret)
+		goto unlock;
+
+	ret = scoutfs_dirty_inode_item(inode, lock);
+	if (ret < 0)
+		goto release;
+
+	/* creating offline extent first, it might fail */
+	if (iax->x_flags & SCOUTFS_IOC_IAX_F_SIZE_OFFLINE) {
+		ret = scoutfs_data_init_offline_extent(inode, iax->size, lock);
+		if (ret)
+			goto release;
+	}
+
+	/* make all changes once they're all checked and will succeed */
+	if (iax->x_mask & SCOUTFS_IOC_IAX_DATA_VERSION)
+		scoutfs_inode_set_data_version(inode, iax->data_version);
+	if (iax->x_mask & SCOUTFS_IOC_IAX_SIZE)
+		i_size_write(inode, iax->size);
+	if (iax->x_mask & SCOUTFS_IOC_IAX_CTIME) {
+		inode->i_ctime.tv_sec = iax->ctime_sec;
+		inode->i_ctime.tv_nsec = iax->ctime_nsec;
+	}
+	if (iax->x_mask & SCOUTFS_IOC_IAX_CRTIME) {
+		si->crtime.tv_sec = iax->crtime_sec;
+		si->crtime.tv_nsec = iax->crtime_nsec;
+	}
+
+	scoutfs_update_inode_item(inode, lock, &ind_locks);
+	ret = 0;
+release:
+	scoutfs_release_trans(sb);
+unlock:
+	scoutfs_inode_index_unlock(sb, &ind_locks);
+	scoutfs_unlock(sb, lock, SCOUTFS_LOCK_WRITE);
+	inode_unlock(inode);
+out:
+	return ret;
+}
diff --git a/kmod/src/attr_x.h b/kmod/src/attr_x.h
new file mode 100644
index 00000000..2aaf8f98
--- /dev/null
+++ b/kmod/src/attr_x.h
@@ -0,0 +1,11 @@
+#ifndef _SCOUTFS_ATTR_X_H_
+#define _SCOUTFS_ATTR_X_H_
+
+#include <linux/kernel.h>
+#include <linux/fs.h>
+#include "ioctl.h"
+
+int scoutfs_get_attr_x(struct inode *inode, struct scoutfs_ioctl_inode_attr_x *iax);
+int scoutfs_set_attr_x(struct inode *inode, struct scoutfs_ioctl_inode_attr_x *iax);
+
+#endif
diff --git a/kmod/src/ioctl.c b/kmod/src/ioctl.c
index 885ad330..74abcf1d 100644
--- a/kmod/src/ioctl.c
+++ b/kmod/src/ioctl.c
@@ -42,6 +42,7 @@
 #include "alloc.h"
 #include "server.h"
 #include "counters.h"
+#include "attr_x.h"
 #include "scoutfs_trace.h"
 
 /*
@@ -1504,6 +1505,68 @@ out:
 	return nr ?: ret;
 }
 
+static long scoutfs_ioc_get_attr_x(struct file *file, unsigned long arg)
+{
+	struct inode *inode = file_inode(file);
+	struct scoutfs_ioctl_inode_attr_x __user *uiax = (void __user *)arg;
+	struct scoutfs_ioctl_inode_attr_x *iax = NULL;
+	int ret;
+
+	iax = kmalloc(sizeof(struct scoutfs_ioctl_inode_attr_x), GFP_KERNEL);
+	if (!iax) {
+		ret = -ENOMEM;
+		goto out;
+	}
+
+	ret = get_user(iax->x_mask, &uiax->x_mask) ?:
+	      get_user(iax->x_flags, &uiax->x_flags);
+	if (ret < 0)
+		goto out;
+
+	ret = scoutfs_get_attr_x(inode, iax);
+	if (ret < 0)
+		goto out;
+
+	/* only copy results after dropping cluster locks (could fault) */
+	if (ret > 0 && copy_to_user(uiax, iax, ret) != 0)
+		ret = -EFAULT;
+	else
+		ret = 0;
+out:
+	kfree(iax);
+	return ret;
+}
+
+static long scoutfs_ioc_set_attr_x(struct file *file, unsigned long arg)
+{
+	struct inode *inode = file_inode(file);
+	struct scoutfs_ioctl_inode_attr_x __user *uiax = (void __user *)arg;
+	struct scoutfs_ioctl_inode_attr_x *iax = NULL;
+	int ret;
+
+	iax = kmalloc(sizeof(struct scoutfs_ioctl_inode_attr_x), GFP_KERNEL);
+	if (!iax) {
+		ret = -ENOMEM;
+		goto out;
+	}
+
+	if (copy_from_user(iax, uiax, sizeof(struct scoutfs_ioctl_inode_attr_x))) {
+		ret = -EFAULT;
+		goto out;
+	}
+
+	ret = mnt_want_write_file(file);
+	if (ret < 0)
+		goto out;
+
+	ret = scoutfs_set_attr_x(inode, iax);
+
+	mnt_drop_write_file(file);
+out:
+	kfree(iax);
+	return ret;
+}
+
 long scoutfs_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 {
 	switch (cmd) {
@@ -1541,6 +1604,10 @@ long scoutfs_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 		return scoutfs_ioc_get_allocated_inos(file, arg);
 	case SCOUTFS_IOC_GET_REFERRING_ENTRIES:
 		return scoutfs_ioc_get_referring_entries(file, arg);
+	case SCOUTFS_IOC_GET_ATTR_X:
+		return scoutfs_ioc_get_attr_x(file, arg);
+	case SCOUTFS_IOC_SET_ATTR_X:
+		return scoutfs_ioc_set_attr_x(file, arg);
 	}
 
 	return -ENOTTY;
diff --git a/kmod/src/ioctl.h b/kmod/src/ioctl.h
index 7be22dbb..d62f0283 100644
--- a/kmod/src/ioctl.h
+++ b/kmod/src/ioctl.h
@@ -673,4 +673,58 @@ struct scoutfs_ioctl_dirent {
 #define SCOUTFS_IOC_GET_REFERRING_ENTRIES \
 	_IOW(SCOUTFS_IOCTL_MAGIC, 17, struct scoutfs_ioctl_get_referring_entries)
 
+struct scoutfs_ioctl_inode_attr_x {
+	__u64 x_mask;
+	__u64 x_flags;
+	__u64 meta_seq;
+	__u64 data_seq;
+	__u64 data_version;
+	__u64 online_blocks;
+	__u64 offline_blocks;
+	__u64 ctime_sec;
+	__u32 ctime_nsec;
+	__u32 crtime_nsec;
+	__u64 crtime_sec;
+	__u64 size;
+};
+
+/*
+ * Behavioral flags set in the x_flags field.  These flags don't
+ * necessarily correspond to specific attributes, but instead change the
+ * behaviour of a _get_ or _set_ operation.
+ *
+ * @SCOUTFS_IOC_IAX_F_SIZE_OFFLINE: When setting i_size, also create
+ * extents which are marked offline for the region of the file from
+ * offset 0 to the new set size.  This can only be set when setting the
+ * size and has no effect if setting the size fails.
+ */
+#define SCOUTFS_IOC_IAX_F_SIZE_OFFLINE	(1ULL << 0)
+#define SCOUTFS_IOC_IAX_F__UNKNOWN	(U64_MAX << 1)
+
+/*
+ * x_mask bits which indicate which attributes of the inode to populate
+ * on return for _get or to set on the inode for _set.  Each mask bit
+ * corresponds to the matching named field in the attr_x struct passed
+ * to the _get_ and _set_ calls.
+ *
+ * Each field can have different permissions or other attribute
+ * requirements which can cause calls to fail.  If _set_ fails then no
+ * other attribute changes will have been made by the same call.
+ */
+#define SCOUTFS_IOC_IAX_META_SEQ	(1ULL << 0)
+#define SCOUTFS_IOC_IAX_DATA_SEQ	(1ULL << 1)
+#define SCOUTFS_IOC_IAX_DATA_VERSION	(1ULL << 2)
+#define SCOUTFS_IOC_IAX_ONLINE_BLOCKS	(1ULL << 3)
+#define SCOUTFS_IOC_IAX_OFFLINE_BLOCKS	(1ULL << 4)
+#define SCOUTFS_IOC_IAX_CTIME		(1ULL << 5)
+#define SCOUTFS_IOC_IAX_CRTIME		(1ULL << 6)
+#define SCOUTFS_IOC_IAX_SIZE		(1ULL << 7)
+#define SCOUTFS_IOC_IAX__UNKNOWN	(U64_MAX << 8)
+
+#define SCOUTFS_IOC_GET_ATTR_X \
+	_IOW(SCOUTFS_IOCTL_MAGIC, 18, struct scoutfs_ioctl_inode_attr_x)
+
+#define SCOUTFS_IOC_SET_ATTR_X \
+	_IOW(SCOUTFS_IOCTL_MAGIC, 19, struct scoutfs_ioctl_inode_attr_x)
+
 #endif