1 files changed, 804 insertions, 0 deletions

diff --git a/fs/xfs/xfs_exchrange.c b/fs/xfs/xfs_exchrange.c
new file mode 100644
index 000000000000..c8a655c92c92
--- /dev/null
+++ b/fs/xfs/xfs_exchrange.c
@@ -0,0 +1,804 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (c) 2020-2024 Oracle.  All Rights Reserved.
+ * Author: Darrick J. Wong <djwong@kernel.org>
+ */
+#include "xfs.h"
+#include "xfs_shared.h"
+#include "xfs_format.h"
+#include "xfs_log_format.h"
+#include "xfs_trans_resv.h"
+#include "xfs_mount.h"
+#include "xfs_defer.h"
+#include "xfs_inode.h"
+#include "xfs_trans.h"
+#include "xfs_quota.h"
+#include "xfs_bmap_util.h"
+#include "xfs_reflink.h"
+#include "xfs_trace.h"
+#include "xfs_exchrange.h"
+#include "xfs_exchmaps.h"
+#include "xfs_sb.h"
+#include "xfs_icache.h"
+#include "xfs_log.h"
+#include "xfs_rtbitmap.h"
+#include <linux/fsnotify.h>
+
+/* Lock (and optionally join) two inodes for a file range exchange. */
+void
+xfs_exchrange_ilock(
+	struct xfs_trans	*tp,
+	struct xfs_inode	*ip1,
+	struct xfs_inode	*ip2)
+{
+	if (ip1 != ip2)
+		xfs_lock_two_inodes(ip1, XFS_ILOCK_EXCL,
+				    ip2, XFS_ILOCK_EXCL);
+	else
+		xfs_ilock(ip1, XFS_ILOCK_EXCL);
+	if (tp) {
+		xfs_trans_ijoin(tp, ip1, 0);
+		if (ip2 != ip1)
+			xfs_trans_ijoin(tp, ip2, 0);
+	}
+
+}
+
+/* Unlock two inodes after a file range exchange operation. */
+void
+xfs_exchrange_iunlock(
+	struct xfs_inode	*ip1,
+	struct xfs_inode	*ip2)
+{
+	if (ip2 != ip1)
+		xfs_iunlock(ip2, XFS_ILOCK_EXCL);
+	xfs_iunlock(ip1, XFS_ILOCK_EXCL);
+}
+
+/*
+ * Estimate the resource requirements to exchange file contents between the two
+ * files.  The caller is required to hold the IOLOCK and the MMAPLOCK and to
+ * have flushed both inodes' pagecache and active direct-ios.
+ */
+int
+xfs_exchrange_estimate(
+	struct xfs_exchmaps_req	*req)
+{
+	int			error;
+
+	xfs_exchrange_ilock(NULL, req->ip1, req->ip2);
+	error = xfs_exchmaps_estimate(req);
+	xfs_exchrange_iunlock(req->ip1, req->ip2);
+	return error;
+}
+
+#define QRETRY_IP1	(0x1)
+#define QRETRY_IP2	(0x2)
+
+/*
+ * Obtain a quota reservation to make sure we don't hit EDQUOT.  We can skip
+ * this if quota enforcement is disabled or if both inodes' dquots are the
+ * same.  The qretry structure must be initialized to zeroes before the first
+ * call to this function.
+ */
+STATIC int
+xfs_exchrange_reserve_quota(
+	struct xfs_trans		*tp,
+	const struct xfs_exchmaps_req	*req,
+	unsigned int			*qretry)
+{
+	int64_t				ddelta, rdelta;
+	int				ip1_error = 0;
+	int				error;
+
+	/*
+	 * Don't bother with a quota reservation if we're not enforcing them
+	 * or the two inodes have the same dquots.
+	 */
+	if (!XFS_IS_QUOTA_ON(tp->t_mountp) || req->ip1 == req->ip2 ||
+	    (req->ip1->i_udquot == req->ip2->i_udquot &&
+	     req->ip1->i_gdquot == req->ip2->i_gdquot &&
+	     req->ip1->i_pdquot == req->ip2->i_pdquot))
+		return 0;
+
+	*qretry = 0;
+
+	/*
+	 * For each file, compute the net gain in the number of regular blocks
+	 * that will be mapped into that file and reserve that much quota.  The
+	 * quota counts must be able to absorb at least that much space.
+	 */
+	ddelta = req->ip2_bcount - req->ip1_bcount;
+	rdelta = req->ip2_rtbcount - req->ip1_rtbcount;
+	if (ddelta > 0 || rdelta > 0) {
+		error = xfs_trans_reserve_quota_nblks(tp, req->ip1,
+				ddelta > 0 ? ddelta : 0,
+				rdelta > 0 ? rdelta : 0,
+				false);
+		if (error == -EDQUOT || error == -ENOSPC) {
+			/*
+			 * Save this error and see what happens if we try to
+			 * reserve quota for ip2.  Then report both.
+			 */
+			*qretry |= QRETRY_IP1;
+			ip1_error = error;
+			error = 0;
+		}
+		if (error)
+			return error;
+	}
+	if (ddelta < 0 || rdelta < 0) {
+		error = xfs_trans_reserve_quota_nblks(tp, req->ip2,
+				ddelta < 0 ? -ddelta : 0,
+				rdelta < 0 ? -rdelta : 0,
+				false);
+		if (error == -EDQUOT || error == -ENOSPC)
+			*qretry |= QRETRY_IP2;
+		if (error)
+			return error;
+	}
+	if (ip1_error)
+		return ip1_error;
+
+	/*
+	 * For each file, forcibly reserve the gross gain in mapped blocks so
+	 * that we don't trip over any quota block reservation assertions.
+	 * We must reserve the gross gain because the quota code subtracts from
+	 * bcount the number of blocks that we unmap; it does not add that
+	 * quantity back to the quota block reservation.
+	 */
+	error = xfs_trans_reserve_quota_nblks(tp, req->ip1, req->ip1_bcount,
+			req->ip1_rtbcount, true);
+	if (error)
+		return error;
+
+	return xfs_trans_reserve_quota_nblks(tp, req->ip2, req->ip2_bcount,
+			req->ip2_rtbcount, true);
+}
+
+/* Exchange the mappings (and hence the contents) of two files' forks. */
+STATIC int
+xfs_exchrange_mappings(
+	const struct xfs_exchrange	*fxr,
+	struct xfs_inode		*ip1,
+	struct xfs_inode		*ip2)
+{
+	struct xfs_mount		*mp = ip1->i_mount;
+	struct xfs_exchmaps_req		req = {
+		.ip1			= ip1,
+		.ip2			= ip2,
+		.startoff1		= XFS_B_TO_FSBT(mp, fxr->file1_offset),
+		.startoff2		= XFS_B_TO_FSBT(mp, fxr->file2_offset),
+		.blockcount		= XFS_B_TO_FSB(mp, fxr->length),
+	};
+	struct xfs_trans		*tp;
+	unsigned int			qretry;
+	bool				retried = false;
+	int				error;
+
+	trace_xfs_exchrange_mappings(fxr, ip1, ip2);
+
+	if (fxr->flags & XFS_EXCHANGE_RANGE_TO_EOF)
+		req.flags |= XFS_EXCHMAPS_SET_SIZES;
+	if (fxr->flags & XFS_EXCHANGE_RANGE_FILE1_WRITTEN)
+		req.flags |= XFS_EXCHMAPS_INO1_WRITTEN;
+
+	/*
+	 * Round the request length up to the nearest file allocation unit.
+	 * The prep function already checked that the request offsets and
+	 * length in @fxr are safe to round up.
+	 */
+	if (xfs_inode_has_bigrtalloc(ip2))
+		req.blockcount = xfs_rtb_roundup_rtx(mp, req.blockcount);
+
+	error = xfs_exchrange_estimate(&req);
+	if (error)
+		return error;
+
+retry:
+	/* Allocate the transaction, lock the inodes, and join them. */
+	error = xfs_trans_alloc(mp, &M_RES(mp)->tr_write, req.resblks, 0,
+			XFS_TRANS_RES_FDBLKS, &tp);
+	if (error)
+		return error;
+
+	xfs_exchrange_ilock(tp, ip1, ip2);
+
+	trace_xfs_exchrange_before(ip2, 2);
+	trace_xfs_exchrange_before(ip1, 1);
+
+	error = xfs_exchmaps_check_forks(mp, &req);
+	if (error)
+		goto out_trans_cancel;
+
+	/*
+	 * Reserve ourselves some quota if any of them are in enforcing mode.
+	 * In theory we only need enough to satisfy the change in the number
+	 * of blocks between the two ranges being remapped.
+	 */
+	error = xfs_exchrange_reserve_quota(tp, &req, &qretry);
+	if ((error == -EDQUOT || error == -ENOSPC) && !retried) {
+		xfs_trans_cancel(tp);
+		xfs_exchrange_iunlock(ip1, ip2);
+		if (qretry & QRETRY_IP1)
+			xfs_blockgc_free_quota(ip1, 0);
+		if (qretry & QRETRY_IP2)
+			xfs_blockgc_free_quota(ip2, 0);
+		retried = true;
+		goto retry;
+	}
+	if (error)
+		goto out_trans_cancel;
+
+	/* If we got this far on a dry run, all parameters are ok. */
+	if (fxr->flags & XFS_EXCHANGE_RANGE_DRY_RUN)
+		goto out_trans_cancel;
+
+	/* Update the mtime and ctime of both files. */
+	if (fxr->flags & __XFS_EXCHANGE_RANGE_UPD_CMTIME1)
+		xfs_trans_ichgtime(tp, ip1, XFS_ICHGTIME_MOD | XFS_ICHGTIME_CHG);
+	if (fxr->flags & __XFS_EXCHANGE_RANGE_UPD_CMTIME2)
+		xfs_trans_ichgtime(tp, ip2, XFS_ICHGTIME_MOD | XFS_ICHGTIME_CHG);
+
+	xfs_exchange_mappings(tp, &req);
+
+	/*
+	 * Force the log to persist metadata updates if the caller or the
+	 * administrator requires this.  The generic prep function already
+	 * flushed the relevant parts of the page cache.
+	 */
+	if (xfs_has_wsync(mp) || (fxr->flags & XFS_EXCHANGE_RANGE_DSYNC))
+		xfs_trans_set_sync(tp);
+
+	error = xfs_trans_commit(tp);
+
+	trace_xfs_exchrange_after(ip2, 2);
+	trace_xfs_exchrange_after(ip1, 1);
+
+	if (error)
+		goto out_unlock;
+
+	/*
+	 * If the caller wanted us to exchange the contents of two complete
+	 * files of unequal length, exchange the incore sizes now.  This should
+	 * be safe because we flushed both files' page caches, exchanged all
+	 * the mappings, and updated the ondisk sizes.
+	 */
+	if (fxr->flags & XFS_EXCHANGE_RANGE_TO_EOF) {
+		loff_t	temp;
+
+		temp = i_size_read(VFS_I(ip2));
+		i_size_write(VFS_I(ip2), i_size_read(VFS_I(ip1)));
+		i_size_write(VFS_I(ip1), temp);
+	}
+
+out_unlock:
+	xfs_exchrange_iunlock(ip1, ip2);
+	return error;
+
+out_trans_cancel:
+	xfs_trans_cancel(tp);
+	goto out_unlock;
+}
+
+/*
+ * Generic code for exchanging ranges of two files via XFS_IOC_EXCHANGE_RANGE.
+ * This part deals with struct file objects and byte ranges and does not deal
+ * with XFS-specific data structures such as xfs_inodes and block ranges.  This
+ * separation may some day facilitate porting to another filesystem.
+ *
+ * The goal is to exchange fxr.length bytes starting at fxr.file1_offset in
+ * file1 with the same number of bytes starting at fxr.file2_offset in file2.
+ * Implementations must call xfs_exchange_range_prep to prepare the two
+ * files prior to taking locks; and they must update the inode change and mod
+ * times of both files as part of the metadata update.  The timestamp update
+ * and freshness checks must be done atomically as part of the data exchange
+ * operation to ensure correctness of the freshness check.
+ * xfs_exchange_range_finish must be called after the operation completes
+ * successfully but before locks are dropped.
+ */
+
+/* Verify that we have security clearance to perform this operation. */
+static int
+xfs_exchange_range_verify_area(
+	struct xfs_exchrange	*fxr)
+{
+	int			ret;
+
+	ret = remap_verify_area(fxr->file1, fxr->file1_offset, fxr->length,
+			true);
+	if (ret)
+		return ret;
+
+	return remap_verify_area(fxr->file2, fxr->file2_offset, fxr->length,
+			true);
+}
+
+/*
+ * Performs necessary checks before doing a range exchange, having stabilized
+ * mutable inode attributes via i_rwsem.
+ */
+static inline int
+xfs_exchange_range_checks(
+	struct xfs_exchrange	*fxr,
+	unsigned int		alloc_unit)
+{
+	struct inode		*inode1 = file_inode(fxr->file1);
+	struct inode		*inode2 = file_inode(fxr->file2);
+	uint64_t		allocmask = alloc_unit - 1;
+	int64_t			test_len;
+	uint64_t		blen;
+	loff_t			size1, size2, tmp;
+	int			error;
+
+	/* Don't touch certain kinds of inodes */
+	if (IS_IMMUTABLE(inode1) || IS_IMMUTABLE(inode2))
+		return -EPERM;
+	if (IS_SWAPFILE(inode1) || IS_SWAPFILE(inode2))
+		return -ETXTBSY;
+
+	size1 = i_size_read(inode1);
+	size2 = i_size_read(inode2);
+
+	/* Ranges cannot start after EOF. */
+	if (fxr->file1_offset > size1 || fxr->file2_offset > size2)
+		return -EINVAL;
+
+	/*
+	 * If the caller said to exchange to EOF, we set the length of the
+	 * request large enough to cover everything to the end of both files.
+	 */
+	if (fxr->flags & XFS_EXCHANGE_RANGE_TO_EOF) {
+		fxr->length = max_t(int64_t, size1 - fxr->file1_offset,
+					     size2 - fxr->file2_offset);
+
+		error = xfs_exchange_range_verify_area(fxr);
+		if (error)
+			return error;
+	}
+
+	/*
+	 * The start of both ranges must be aligned to the file allocation
+	 * unit.
+	 */
+	if (!IS_ALIGNED(fxr->file1_offset, alloc_unit) ||
+	    !IS_ALIGNED(fxr->file2_offset, alloc_unit))
+		return -EINVAL;
+
+	/* Ensure offsets don't wrap. */
+	if (check_add_overflow(fxr->file1_offset, fxr->length, &tmp) ||
+	    check_add_overflow(fxr->file2_offset, fxr->length, &tmp))
+		return -EINVAL;
+
+	/*
+	 * We require both ranges to end within EOF, unless we're exchanging
+	 * to EOF.
+	 */
+	if (!(fxr->flags & XFS_EXCHANGE_RANGE_TO_EOF) &&
+	    (fxr->file1_offset + fxr->length > size1 ||
+	     fxr->file2_offset + fxr->length > size2))
+		return -EINVAL;
+
+	/*
+	 * Make sure we don't hit any file size limits.  If we hit any size
+	 * limits such that test_length was adjusted, we abort the whole
+	 * operation.
+	 */
+	test_len = fxr->length;
+	error = generic_write_check_limits(fxr->file2, fxr->file2_offset,
+			&test_len);
+	if (error)
+		return error;
+	error = generic_write_check_limits(fxr->file1, fxr->file1_offset,
+			&test_len);
+	if (error)
+		return error;
+	if (test_len != fxr->length)
+		return -EINVAL;
+
+	/*
+	 * If the user wanted us to exchange up to the infile's EOF, round up
+	 * to the next allocation unit boundary for this check.  Do the same
+	 * for the outfile.
+	 *
+	 * Otherwise, reject the range length if it's not aligned to an
+	 * allocation unit.
+	 */
+	if (fxr->file1_offset + fxr->length == size1)
+		blen = ALIGN(size1, alloc_unit) - fxr->file1_offset;
+	else if (fxr->file2_offset + fxr->length == size2)
+		blen = ALIGN(size2, alloc_unit) - fxr->file2_offset;
+	else if (!IS_ALIGNED(fxr->length, alloc_unit))
+		return -EINVAL;
+	else
+		blen = fxr->length;
+
+	/* Don't allow overlapped exchanges within the same file. */
+	if (inode1 == inode2 &&
+	    fxr->file2_offset + blen > fxr->file1_offset &&
+	    fxr->file1_offset + blen > fxr->file2_offset)
+		return -EINVAL;
+
+	/*
+	 * Ensure that we don't exchange a partial EOF block into the middle of
+	 * another file.
+	 */
+	if ((fxr->length & allocmask) == 0)
+		return 0;
+
+	blen = fxr->length;
+	if (fxr->file2_offset + blen < size2)
+		blen &= ~allocmask;
+
+	if (fxr->file1_offset + blen < size1)
+		blen &= ~allocmask;
+
+	return blen == fxr->length ? 0 : -EINVAL;
+}
+
+/*
+ * Check that the two inodes are eligible for range exchanges, the ranges make
+ * sense, and then flush all dirty data.  Caller must ensure that the inodes
+ * have been locked against any other modifications.
+ */
+static inline int
+xfs_exchange_range_prep(
+	struct xfs_exchrange	*fxr,
+	unsigned int		alloc_unit)
+{
+	struct inode		*inode1 = file_inode(fxr->file1);
+	struct inode		*inode2 = file_inode(fxr->file2);
+	bool			same_inode = (inode1 == inode2);
+	int			error;
+
+	/* Check that we don't violate system file offset limits. */
+	error = xfs_exchange_range_checks(fxr, alloc_unit);
+	if (error || fxr->length == 0)
+		return error;
+
+	/* Wait for the completion of any pending IOs on both files */
+	inode_dio_wait(inode1);
+	if (!same_inode)
+		inode_dio_wait(inode2);
+
+	error = filemap_write_and_wait_range(inode1->i_mapping,
+			fxr->file1_offset,
+			fxr->file1_offset + fxr->length - 1);
+	if (error)
+		return error;
+
+	error = filemap_write_and_wait_range(inode2->i_mapping,
+			fxr->file2_offset,
+			fxr->file2_offset + fxr->length - 1);
+	if (error)
+		return error;
+
+	/*
+	 * If the files or inodes involved require synchronous writes, amend
+	 * the request to force the filesystem to flush all data and metadata
+	 * to disk after the operation completes.
+	 */
+	if (((fxr->file1->f_flags | fxr->file2->f_flags) & O_SYNC) ||
+	    IS_SYNC(inode1) || IS_SYNC(inode2))
+		fxr->flags |= XFS_EXCHANGE_RANGE_DSYNC;
+
+	return 0;
+}
+
+/*
+ * Finish a range exchange operation, if it was successful.  Caller must ensure
+ * that the inodes are still locked against any other modifications.
+ */
+static inline int
+xfs_exchange_range_finish(
+	struct xfs_exchrange	*fxr)
+{
+	int			error;
+
+	error = file_remove_privs(fxr->file1);
+	if (error)
+		return error;
+	if (file_inode(fxr->file1) == file_inode(fxr->file2))
+		return 0;
+
+	return file_remove_privs(fxr->file2);
+}
+
+/*
+ * Check the alignment of an exchange request when the allocation unit size
+ * isn't a power of two.  The generic file-level helpers use (fast)
+ * bitmask-based alignment checks, but here we have to use slow long division.
+ */
+static int
+xfs_exchrange_check_rtalign(
+	const struct xfs_exchrange	*fxr,
+	struct xfs_inode		*ip1,
+	struct xfs_inode		*ip2,
+	unsigned int			alloc_unit)
+{
+	uint64_t			length = fxr->length;
+	uint64_t			blen;
+	loff_t				size1, size2;
+
+	size1 = i_size_read(VFS_I(ip1));
+	size2 = i_size_read(VFS_I(ip2));
+
+	/* The start of both ranges must be aligned to a rt extent. */
+	if (!isaligned_64(fxr->file1_offset, alloc_unit) ||
+	    !isaligned_64(fxr->file2_offset, alloc_unit))
+		return -EINVAL;
+
+	if (fxr->flags & XFS_EXCHANGE_RANGE_TO_EOF)
+		length = max_t(int64_t, size1 - fxr->file1_offset,
+					size2 - fxr->file2_offset);
+
+	/*
+	 * If the user wanted us to exchange up to the infile's EOF, round up
+	 * to the next rt extent boundary for this check.  Do the same for the
+	 * outfile.
+	 *
+	 * Otherwise, reject the range length if it's not rt extent aligned.
+	 * We already confirmed the starting offsets' rt extent block
+	 * alignment.
+	 */
+	if (fxr->file1_offset + length == size1)
+		blen = roundup_64(size1, alloc_unit) - fxr->file1_offset;
+	else if (fxr->file2_offset + length == size2)
+		blen = roundup_64(size2, alloc_unit) - fxr->file2_offset;
+	else if (!isaligned_64(length, alloc_unit))
+		return -EINVAL;
+	else
+		blen = length;
+
+	/* Don't allow overlapped exchanges within the same file. */
+	if (ip1 == ip2 &&
+	    fxr->file2_offset + blen > fxr->file1_offset &&
+	    fxr->file1_offset + blen > fxr->file2_offset)
+		return -EINVAL;
+
+	/*
+	 * Ensure that we don't exchange a partial EOF rt extent into the
+	 * middle of another file.
+	 */
+	if (isaligned_64(length, alloc_unit))
+		return 0;
+
+	blen = length;
+	if (fxr->file2_offset + length < size2)
+		blen = rounddown_64(blen, alloc_unit);
+
+	if (fxr->file1_offset + blen < size1)
+		blen = rounddown_64(blen, alloc_unit);
+
+	return blen == length ? 0 : -EINVAL;
+}
+
+/* Prepare two files to have their data exchanged. */
+STATIC int
+xfs_exchrange_prep(
+	struct xfs_exchrange	*fxr,
+	struct xfs_inode	*ip1,
+	struct xfs_inode	*ip2)
+{
+	struct xfs_mount	*mp = ip2->i_mount;
+	unsigned int		alloc_unit = xfs_inode_alloc_unitsize(ip2);
+	int			error;
+
+	trace_xfs_exchrange_prep(fxr, ip1, ip2);
+
+	/* Verify both files are either real-time or non-realtime */
+	if (XFS_IS_REALTIME_INODE(ip1) != XFS_IS_REALTIME_INODE(ip2))
+		return -EINVAL;
+
+	/* Check non-power of two alignment issues, if necessary. */
+	if (!is_power_of_2(alloc_unit)) {
+		error = xfs_exchrange_check_rtalign(fxr, ip1, ip2, alloc_unit);
+		if (error)
+			return error;
+
+		/*
+		 * Do the generic file-level checks with the regular block
+		 * alignment.
+		 */
+		alloc_unit = mp->m_sb.sb_blocksize;
+	}
+
+	error = xfs_exchange_range_prep(fxr, alloc_unit);
+	if (error || fxr->length == 0)
+		return error;
+
+	/* Attach dquots to both inodes before changing block maps. */
+	error = xfs_qm_dqattach(ip2);
+	if (error)
+		return error;
+	error = xfs_qm_dqattach(ip1);
+	if (error)
+		return error;
+
+	trace_xfs_exchrange_flush(fxr, ip1, ip2);
+
+	/* Flush the relevant ranges of both files. */
+	error = xfs_flush_unmap_range(ip2, fxr->file2_offset, fxr->length);
+	if (error)
+		return error;
+	error = xfs_flush_unmap_range(ip1, fxr->file1_offset, fxr->length);
+	if (error)
+		return error;
+
+	/*
+	 * Cancel CoW fork preallocations for the ranges of both files.  The
+	 * prep function should have flushed all the dirty data, so the only
+	 * CoW mappings remaining should be speculative.
+	 */
+	if (xfs_inode_has_cow_data(ip1)) {
+		error = xfs_reflink_cancel_cow_range(ip1, fxr->file1_offset,
+				fxr->length, true);
+		if (error)
+			return error;
+	}
+
+	if (xfs_inode_has_cow_data(ip2)) {
+		error = xfs_reflink_cancel_cow_range(ip2, fxr->file2_offset,
+				fxr->length, true);
+		if (error)
+			return error;
+	}
+
+	return 0;
+}
+
+/*
+ * Exchange contents of files.  This is the binding between the generic
+ * file-level concepts and the XFS inode-specific implementation.
+ */
+STATIC int
+xfs_exchrange_contents(
+	struct xfs_exchrange	*fxr)
+{
+	struct inode		*inode1 = file_inode(fxr->file1);
+	struct inode		*inode2 = file_inode(fxr->file2);
+	struct xfs_inode	*ip1 = XFS_I(inode1);
+	struct xfs_inode	*ip2 = XFS_I(inode2);
+	struct xfs_mount	*mp = ip1->i_mount;
+	int			error;
+
+	if (!xfs_has_exchange_range(mp))
+		return -EOPNOTSUPP;
+
+	if (fxr->flags & ~(XFS_EXCHANGE_RANGE_ALL_FLAGS |
+			   XFS_EXCHANGE_RANGE_PRIV_FLAGS))
+		return -EINVAL;
+
+	if (xfs_is_shutdown(mp))
+		return -EIO;
+
+	/* Lock both files against IO */
+	error = xfs_ilock2_io_mmap(ip1, ip2);
+	if (error)
+		goto out_err;
+
+	/* Prepare and then exchange file contents. */
+	error = xfs_exchrange_prep(fxr, ip1, ip2);
+	if (error)
+		goto out_unlock;
+
+	error = xfs_exchrange_mappings(fxr, ip1, ip2);
+	if (error)
+		goto out_unlock;
+
+	/*
+	 * Finish the exchange by removing special file privileges like any
+	 * other file write would do.  This may involve turning on support for
+	 * logged xattrs if either file has security capabilities.
+	 */
+	error = xfs_exchange_range_finish(fxr);
+	if (error)
+		goto out_unlock;
+
+out_unlock:
+	xfs_iunlock2_io_mmap(ip1, ip2);
+out_err:
+	if (error)
+		trace_xfs_exchrange_error(ip2, error, _RET_IP_);
+	return error;
+}
+
+/* Exchange parts of two files. */
+static int
+xfs_exchange_range(
+	struct xfs_exchrange	*fxr)
+{
+	struct inode		*inode1 = file_inode(fxr->file1);
+	struct inode		*inode2 = file_inode(fxr->file2);
+	int			ret;
+
+	BUILD_BUG_ON(XFS_EXCHANGE_RANGE_ALL_FLAGS &
+		     XFS_EXCHANGE_RANGE_PRIV_FLAGS);
+
+	/* Both files must be on the same mount/filesystem. */
+	if (fxr->file1->f_path.mnt != fxr->file2->f_path.mnt)
+		return -EXDEV;
+
+	if (fxr->flags & ~XFS_EXCHANGE_RANGE_ALL_FLAGS)
+		return -EINVAL;
+
+	/* Userspace requests only honored for regular files. */
+	if (S_ISDIR(inode1->i_mode) || S_ISDIR(inode2->i_mode))
+		return -EISDIR;
+	if (!S_ISREG(inode1->i_mode) || !S_ISREG(inode2->i_mode))
+		return -EINVAL;
+
+	/* Both files must be opened for read and write. */
+	if (!(fxr->file1->f_mode & FMODE_READ) ||
+	    !(fxr->file1->f_mode & FMODE_WRITE) ||
+	    !(fxr->file2->f_mode & FMODE_READ) ||
+	    !(fxr->file2->f_mode & FMODE_WRITE))
+		return -EBADF;
+
+	/* Neither file can be opened append-only. */
+	if ((fxr->file1->f_flags & O_APPEND) ||
+	    (fxr->file2->f_flags & O_APPEND))
+		return -EBADF;
+
+	/*
+	 * If we're not exchanging to EOF, we can check the areas before
+	 * stabilizing both files' i_size.
+	 */
+	if (!(fxr->flags & XFS_EXCHANGE_RANGE_TO_EOF)) {
+		ret = xfs_exchange_range_verify_area(fxr);
+		if (ret)
+			return ret;
+	}
+
+	/* Update cmtime if the fd/inode don't forbid it. */
+	if (!(fxr->file1->f_mode & FMODE_NOCMTIME) && !IS_NOCMTIME(inode1))
+		fxr->flags |= __XFS_EXCHANGE_RANGE_UPD_CMTIME1;
+	if (!(fxr->file2->f_mode & FMODE_NOCMTIME) && !IS_NOCMTIME(inode2))
+		fxr->flags |= __XFS_EXCHANGE_RANGE_UPD_CMTIME2;
+
+	file_start_write(fxr->file2);
+	ret = xfs_exchrange_contents(fxr);
+	file_end_write(fxr->file2);
+	if (ret)
+		return ret;
+
+	fsnotify_modify(fxr->file1);
+	if (fxr->file2 != fxr->file1)
+		fsnotify_modify(fxr->file2);
+	return 0;
+}
+
+/* Collect exchange-range arguments from userspace. */
+long
+xfs_ioc_exchange_range(
+	struct file			*file,
+	struct xfs_exchange_range __user *argp)
+{
+	struct xfs_exchrange		fxr = {
+		.file2			= file,
+	};
+	struct xfs_exchange_range	args;
+	struct fd			file1;
+	int				error;
+
+	if (copy_from_user(&args, argp, sizeof(args)))
+		return -EFAULT;
+	if (memchr_inv(&args.pad, 0, sizeof(args.pad)))
+		return -EINVAL;
+	if (args.flags & ~XFS_EXCHANGE_RANGE_ALL_FLAGS)
+		return -EINVAL;
+
+	fxr.file1_offset	= args.file1_offset;
+	fxr.file2_offset	= args.file2_offset;
+	fxr.length		= args.length;
+	fxr.flags		= args.flags;
+
+	file1 = fdget(args.file1_fd);
+	if (!file1.file)
+		return -EBADF;
+	fxr.file1 = file1.file;
+
+	error = xfs_exchange_range(&fxr);
+	fdput(file1);
+	return error;
+}