Re: [PATCH 06/18] xfs: introduce a swap-extent log intent item

[Allison Henderson <allison.henderson@oracle.com>]

On 3/31/21 6:09 PM, Darrick J. Wong wrote:
> From: Darrick J. Wong <djwong@kernel.org>
> 
> Introduce a new intent log item to handle swapping extents.
> 
> Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Looks ok to me.  Seems reasonably similar to existing log items.
Reviewed-by: Allison Henderson <allison.henderson@oracle.com>

> ---
>   fs/xfs/Makefile                 |    1
>   fs/xfs/libxfs/xfs_log_format.h  |   59 +++++++
>   fs/xfs/libxfs/xfs_log_recover.h |    2
>   fs/xfs/xfs_log.c                |    2
>   fs/xfs/xfs_log_recover.c        |    2
>   fs/xfs/xfs_super.c              |   17 ++
>   fs/xfs/xfs_swapext_item.c       |  328 +++++++++++++++++++++++++++++++++++++++
>   fs/xfs/xfs_swapext_item.h       |   61 +++++++
>   8 files changed, 470 insertions(+), 2 deletions(-)
>   create mode 100644 fs/xfs/xfs_swapext_item.c
>   create mode 100644 fs/xfs/xfs_swapext_item.h
> 
> 
> diff --git a/fs/xfs/Makefile b/fs/xfs/Makefile
> index dac3bec1a695..a7cc6f496ad0 100644
> --- a/fs/xfs/Makefile
> +++ b/fs/xfs/Makefile
> @@ -107,6 +107,7 @@ xfs-y				+= xfs_log.o \
>   				   xfs_inode_item_recover.o \
>   				   xfs_refcount_item.o \
>   				   xfs_rmap_item.o \
> +				   xfs_swapext_item.o \
>   				   xfs_log_recover.o \
>   				   xfs_trans_ail.o \
>   				   xfs_trans_buf.o
> diff --git a/fs/xfs/libxfs/xfs_log_format.h b/fs/xfs/libxfs/xfs_log_format.h
> index 6107dac4bd6b..52ca6d72de6a 100644
> --- a/fs/xfs/libxfs/xfs_log_format.h
> +++ b/fs/xfs/libxfs/xfs_log_format.h
> @@ -117,7 +117,9 @@ struct xfs_unmount_log_format {
>   #define XLOG_REG_TYPE_CUD_FORMAT	24
>   #define XLOG_REG_TYPE_BUI_FORMAT	25
>   #define XLOG_REG_TYPE_BUD_FORMAT	26
> -#define XLOG_REG_TYPE_MAX		26
> +#define XLOG_REG_TYPE_SXI_FORMAT	27
> +#define XLOG_REG_TYPE_SXD_FORMAT	28
> +#define XLOG_REG_TYPE_MAX		28
>   
>   /*
>    * Flags to log operation header
> @@ -240,6 +242,8 @@ typedef struct xfs_trans_header {
>   #define	XFS_LI_CUD		0x1243
>   #define	XFS_LI_BUI		0x1244	/* bmbt update intent */
>   #define	XFS_LI_BUD		0x1245
> +#define	XFS_LI_SXI		0x1246
> +#define	XFS_LI_SXD		0x1247
>   
>   #define XFS_LI_TYPE_DESC \
>   	{ XFS_LI_EFI,		"XFS_LI_EFI" }, \
> @@ -255,7 +259,9 @@ typedef struct xfs_trans_header {
>   	{ XFS_LI_CUI,		"XFS_LI_CUI" }, \
>   	{ XFS_LI_CUD,		"XFS_LI_CUD" }, \
>   	{ XFS_LI_BUI,		"XFS_LI_BUI" }, \
> -	{ XFS_LI_BUD,		"XFS_LI_BUD" }
> +	{ XFS_LI_BUD,		"XFS_LI_BUD" }, \
> +	{ XFS_LI_SXI,		"XFS_LI_SXI" }, \
> +	{ XFS_LI_SXD,		"XFS_LI_SXD" }
>   
>   /*
>    * Inode Log Item Format definitions.
> @@ -784,6 +790,55 @@ struct xfs_bud_log_format {
>   	uint64_t		bud_bui_id;	/* id of corresponding bui */
>   };
>   
> +/*
> + * SXI/SXD (extent swapping) log format definitions
> + */
> +
> +struct xfs_swap_extent {
> +	uint64_t		sx_inode1;
> +	uint64_t		sx_inode2;
> +	uint64_t		sx_startoff1;
> +	uint64_t		sx_startoff2;
> +	uint64_t		sx_blockcount;
> +	uint64_t		sx_flags;
> +	int64_t			sx_isize1;
> +	int64_t			sx_isize2;
> +};
> +
> +/* Swap extents between extended attribute forks. */
> +#define XFS_SWAP_EXTENT_ATTR_FORK	(1ULL << 0)
> +
> +/* Set the file sizes when finished. */
> +#define XFS_SWAP_EXTENT_SET_SIZES	(1ULL << 1)
> +
> +/* Do not swap any part of the range where file1's mapping is a hole. */
> +#define XFS_SWAP_EXTENT_SKIP_FILE1_HOLES (1ULL << 2)
> +
> +#define XFS_SWAP_EXTENT_FLAGS		(XFS_SWAP_EXTENT_ATTR_FORK | \
> +					 XFS_SWAP_EXTENT_SET_SIZES | \
> +					 XFS_SWAP_EXTENT_SKIP_FILE1_HOLES)
> +
> +/* This is the structure used to lay out an sxi log item in the log. */
> +struct xfs_sxi_log_format {
> +	uint16_t		sxi_type;	/* sxi log item type */
> +	uint16_t		sxi_size;	/* size of this item */
> +	uint32_t		__pad;		/* must be zero */
> +	uint64_t		sxi_id;		/* sxi identifier */
> +	struct xfs_swap_extent	sxi_extent;	/* extent to swap */
> +};
> +
> +/*
> + * This is the structure used to lay out an sxd log item in the
> + * log.  The sxd_extents array is a variable size array whose
> + * size is given by sxd_nextents;
> + */
> +struct xfs_sxd_log_format {
> +	uint16_t		sxd_type;	/* sxd log item type */
> +	uint16_t		sxd_size;	/* size of this item */
> +	uint32_t		__pad;
> +	uint64_t		sxd_sxi_id;	/* id of corresponding bui */
> +};
> +
>   /*
>    * Dquot Log format definitions.
>    *
> diff --git a/fs/xfs/libxfs/xfs_log_recover.h b/fs/xfs/libxfs/xfs_log_recover.h
> index 3cca2bfe714c..dcc11a8c438a 100644
> --- a/fs/xfs/libxfs/xfs_log_recover.h
> +++ b/fs/xfs/libxfs/xfs_log_recover.h
> @@ -72,6 +72,8 @@ extern const struct xlog_recover_item_ops xlog_rui_item_ops;
>   extern const struct xlog_recover_item_ops xlog_rud_item_ops;
>   extern const struct xlog_recover_item_ops xlog_cui_item_ops;
>   extern const struct xlog_recover_item_ops xlog_cud_item_ops;
> +extern const struct xlog_recover_item_ops xlog_sxi_item_ops;
> +extern const struct xlog_recover_item_ops xlog_sxd_item_ops;
>   
>   /*
>    * Macros, structures, prototypes for internal log manager use.
> diff --git a/fs/xfs/xfs_log.c b/fs/xfs/xfs_log.c
> index cb72be62da3e..34213fce3eed 100644
> --- a/fs/xfs/xfs_log.c
> +++ b/fs/xfs/xfs_log.c
> @@ -2113,6 +2113,8 @@ xlog_print_tic_res(
>   	    REG_TYPE_STR(CUD_FORMAT, "cud_format"),
>   	    REG_TYPE_STR(BUI_FORMAT, "bui_format"),
>   	    REG_TYPE_STR(BUD_FORMAT, "bud_format"),
> +	    REG_TYPE_STR(SXI_FORMAT, "sxi_format"),
> +	    REG_TYPE_STR(SXD_FORMAT, "sxd_format"),
>   	};
>   	BUILD_BUG_ON(ARRAY_SIZE(res_type_str) != XLOG_REG_TYPE_MAX + 1);
>   #undef REG_TYPE_STR
> diff --git a/fs/xfs/xfs_log_recover.c b/fs/xfs/xfs_log_recover.c
> index fdba9b55822e..107bb222d79f 100644
> --- a/fs/xfs/xfs_log_recover.c
> +++ b/fs/xfs/xfs_log_recover.c
> @@ -1775,6 +1775,8 @@ static const struct xlog_recover_item_ops *xlog_recover_item_ops[] = {
>   	&xlog_cud_item_ops,
>   	&xlog_bui_item_ops,
>   	&xlog_bud_item_ops,
> +	&xlog_sxi_item_ops,
> +	&xlog_sxd_item_ops,
>   };
>   
>   static const struct xlog_recover_item_ops *
> diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
> index 175dc7acaca8..85ced8cc6070 100644
> --- a/fs/xfs/xfs_super.c
> +++ b/fs/xfs/xfs_super.c
> @@ -36,6 +36,7 @@
>   #include "xfs_bmap_item.h"
>   #include "xfs_reflink.h"
>   #include "xfs_pwork.h"
> +#include "xfs_swapext_item.h"
>   
>   #include <linux/magic.h>
>   #include <linux/fs_context.h>
> @@ -2121,8 +2122,24 @@ xfs_init_zones(void)
>   	if (!xfs_bui_zone)
>   		goto out_destroy_bud_zone;
>   
> +	xfs_sxd_zone = kmem_cache_create("xfs_sxd_item",
> +					 sizeof(struct xfs_sxd_log_item),
> +					 0, 0, NULL);
> +	if (!xfs_sxd_zone)
> +		goto out_destroy_bui_zone;
> +
> +	xfs_sxi_zone = kmem_cache_create("xfs_sxi_item",
> +					 sizeof(struct xfs_sxi_log_item),
> +					 0, 0, NULL);
> +	if (!xfs_sxi_zone)
> +		goto out_destroy_sxd_zone;
> +
>   	return 0;
>   
> + out_destroy_sxd_zone:
> +	kmem_cache_destroy(xfs_sxd_zone);
> + out_destroy_bui_zone:
> +	kmem_cache_destroy(xfs_bui_zone);
>    out_destroy_bud_zone:
>   	kmem_cache_destroy(xfs_bud_zone);
>    out_destroy_cui_zone:
> diff --git a/fs/xfs/xfs_swapext_item.c b/fs/xfs/xfs_swapext_item.c
> new file mode 100644
> index 000000000000..83913e9fd4d4
> --- /dev/null
> +++ b/fs/xfs/xfs_swapext_item.c
> @@ -0,0 +1,328 @@
> +// SPDX-License-Identifier: GPL-2.0-or-later
> +/*
> + * Copyright (C) 2021 Oracle.  All Rights Reserved.
> + * Author: Darrick J. Wong <djwong@kernel.org>
> + */
> +#include "xfs.h"
> +#include "xfs_fs.h"
> +#include "xfs_format.h"
> +#include "xfs_log_format.h"
> +#include "xfs_trans_resv.h"
> +#include "xfs_bit.h"
> +#include "xfs_shared.h"
> +#include "xfs_mount.h"
> +#include "xfs_defer.h"
> +#include "xfs_inode.h"
> +#include "xfs_trans.h"
> +#include "xfs_trans_priv.h"
> +#include "xfs_swapext_item.h"
> +#include "xfs_log.h"
> +#include "xfs_bmap.h"
> +#include "xfs_icache.h"
> +#include "xfs_trans_space.h"
> +#include "xfs_error.h"
> +#include "xfs_log_priv.h"
> +#include "xfs_log_recover.h"
> +
> +kmem_zone_t	*xfs_sxi_zone;
> +kmem_zone_t	*xfs_sxd_zone;
> +
> +static const struct xfs_item_ops xfs_sxi_item_ops;
> +
> +static inline struct xfs_sxi_log_item *SXI_ITEM(struct xfs_log_item *lip)
> +{
> +	return container_of(lip, struct xfs_sxi_log_item, sxi_item);
> +}
> +
> +STATIC void
> +xfs_sxi_item_free(
> +	struct xfs_sxi_log_item	*sxi_lip)
> +{
> +	kmem_cache_free(xfs_sxi_zone, sxi_lip);
> +}
> +
> +/*
> + * Freeing the SXI requires that we remove it from the AIL if it has already
> + * been placed there. However, the SXI may not yet have been placed in the AIL
> + * when called by xfs_sxi_release() from SXD processing due to the ordering of
> + * committed vs unpin operations in bulk insert operations. Hence the reference
> + * count to ensure only the last caller frees the SXI.
> + */
> +STATIC void
> +xfs_sxi_release(
> +	struct xfs_sxi_log_item	*sxi_lip)
> +{
> +	ASSERT(atomic_read(&sxi_lip->sxi_refcount) > 0);
> +	if (atomic_dec_and_test(&sxi_lip->sxi_refcount)) {
> +		xfs_trans_ail_delete(&sxi_lip->sxi_item, SHUTDOWN_LOG_IO_ERROR);
> +		xfs_sxi_item_free(sxi_lip);
> +	}
> +}
> +
> +
> +STATIC void
> +xfs_sxi_item_size(
> +	struct xfs_log_item	*lip,
> +	int			*nvecs,
> +	int			*nbytes)
> +{
> +	*nvecs += 1;
> +	*nbytes += sizeof(struct xfs_sxi_log_format);
> +}
> +
> +/*
> + * This is called to fill in the vector of log iovecs for the given sxi log
> + * item. We use only 1 iovec, and we point that at the sxi_log_format structure
> + * embedded in the sxi item.
> + */
> +STATIC void
> +xfs_sxi_item_format(
> +	struct xfs_log_item	*lip,
> +	struct xfs_log_vec	*lv)
> +{
> +	struct xfs_sxi_log_item	*sxi_lip = SXI_ITEM(lip);
> +	struct xfs_log_iovec	*vecp = NULL;
> +
> +	sxi_lip->sxi_format.sxi_type = XFS_LI_SXI;
> +	sxi_lip->sxi_format.sxi_size = 1;
> +
> +	xlog_copy_iovec(lv, &vecp, XLOG_REG_TYPE_SXI_FORMAT,
> +			&sxi_lip->sxi_format,
> +			sizeof(struct xfs_sxi_log_format));
> +}
> +
> +/*
> + * The unpin operation is the last place an SXI is manipulated in the log. It
> + * is either inserted in the AIL or aborted in the event of a log I/O error. In
> + * either case, the SXI transaction has been successfully committed to make it
> + * this far. Therefore, we expect whoever committed the SXI to either construct
> + * and commit the SXD or drop the SXD's reference in the event of error. Simply
> + * drop the log's SXI reference now that the log is done with it.
> + */
> +STATIC void
> +xfs_sxi_item_unpin(
> +	struct xfs_log_item	*lip,
> +	int			remove)
> +{
> +	struct xfs_sxi_log_item	*sxi_lip = SXI_ITEM(lip);
> +
> +	xfs_sxi_release(sxi_lip);
> +}
> +
> +/*
> + * The SXI has been either committed or aborted if the transaction has been
> + * cancelled. If the transaction was cancelled, an SXD isn't going to be
> + * constructed and thus we free the SXI here directly.
> + */
> +STATIC void
> +xfs_sxi_item_release(
> +	struct xfs_log_item	*lip)
> +{
> +	xfs_sxi_release(SXI_ITEM(lip));
> +}
> +
> +/* Allocate and initialize an sxi item with the given number of extents. */
> +STATIC struct xfs_sxi_log_item *
> +xfs_sxi_init(
> +	struct xfs_mount		*mp)
> +
> +{
> +	struct xfs_sxi_log_item		*sxi_lip;
> +
> +	sxi_lip = kmem_cache_zalloc(xfs_sxi_zone, GFP_KERNEL | __GFP_NOFAIL);
> +
> +	xfs_log_item_init(mp, &sxi_lip->sxi_item, XFS_LI_SXI, &xfs_sxi_item_ops);
> +	sxi_lip->sxi_format.sxi_id = (uintptr_t)(void *)sxi_lip;
> +	atomic_set(&sxi_lip->sxi_refcount, 2);
> +
> +	return sxi_lip;
> +}
> +
> +static inline struct xfs_sxd_log_item *SXD_ITEM(struct xfs_log_item *lip)
> +{
> +	return container_of(lip, struct xfs_sxd_log_item, sxd_item);
> +}
> +
> +STATIC void
> +xfs_sxd_item_size(
> +	struct xfs_log_item	*lip,
> +	int			*nvecs,
> +	int			*nbytes)
> +{
> +	*nvecs += 1;
> +	*nbytes += sizeof(struct xfs_sxd_log_format);
> +}
> +
> +/*
> + * This is called to fill in the vector of log iovecs for the given sxd log
> + * item. We use only 1 iovec, and we point that at the sxd_log_format structure
> + * embedded in the sxd item.
> + */
> +STATIC void
> +xfs_sxd_item_format(
> +	struct xfs_log_item	*lip,
> +	struct xfs_log_vec	*lv)
> +{
> +	struct xfs_sxd_log_item	*sxd_lip = SXD_ITEM(lip);
> +	struct xfs_log_iovec	*vecp = NULL;
> +
> +	sxd_lip->sxd_format.sxd_type = XFS_LI_SXD;
> +	sxd_lip->sxd_format.sxd_size = 1;
> +
> +	xlog_copy_iovec(lv, &vecp, XLOG_REG_TYPE_SXD_FORMAT, &sxd_lip->sxd_format,
> +			sizeof(struct xfs_sxd_log_format));
> +}
> +
> +/*
> + * The SXD is either committed or aborted if the transaction is cancelled. If
> + * the transaction is cancelled, drop our reference to the SXI and free the
> + * SXD.
> + */
> +STATIC void
> +xfs_sxd_item_release(
> +	struct xfs_log_item	*lip)
> +{
> +	struct xfs_sxd_log_item	*sxd_lip = SXD_ITEM(lip);
> +
> +	xfs_sxi_release(sxd_lip->sxd_intent_log_item);
> +	kmem_cache_free(xfs_sxd_zone, sxd_lip);
> +}
> +
> +static const struct xfs_item_ops xfs_sxd_item_ops = {
> +	.flags		= XFS_ITEM_RELEASE_WHEN_COMMITTED,
> +	.iop_size	= xfs_sxd_item_size,
> +	.iop_format	= xfs_sxd_item_format,
> +	.iop_release	= xfs_sxd_item_release,
> +};
> +
> +/* Process a swapext update intent item that was recovered from the log. */
> +STATIC int
> +xfs_sxi_item_recover(
> +	struct xfs_log_item		*lip,
> +	struct list_head		*capture_list)
> +{
> +	return -EFSCORRUPTED;
> +}
> +
> +STATIC bool
> +xfs_sxi_item_match(
> +	struct xfs_log_item	*lip,
> +	uint64_t		intent_id)
> +{
> +	return SXI_ITEM(lip)->sxi_format.sxi_id == intent_id;
> +}
> +
> +/* Relog an intent item to push the log tail forward. */
> +static struct xfs_log_item *
> +xfs_sxi_item_relog(
> +	struct xfs_log_item		*intent,
> +	struct xfs_trans		*tp)
> +{
> +	ASSERT(0);
> +	return NULL;
> +}
> +
> +static const struct xfs_item_ops xfs_sxi_item_ops = {
> +	.iop_size	= xfs_sxi_item_size,
> +	.iop_format	= xfs_sxi_item_format,
> +	.iop_unpin	= xfs_sxi_item_unpin,
> +	.iop_release	= xfs_sxi_item_release,
> +	.iop_recover	= xfs_sxi_item_recover,
> +	.iop_match	= xfs_sxi_item_match,
> +	.iop_relog	= xfs_sxi_item_relog,
> +};
> +
> +/*
> + * Copy an SXI format buffer from the given buf, and into the destination SXI
> + * format structure.  The SXI/SXD items were designed not to need any special
> + * alignment handling.
> + */
> +static int
> +xfs_sxi_copy_format(
> +	struct xfs_log_iovec		*buf,
> +	struct xfs_sxi_log_format	*dst_sxi_fmt)
> +{
> +	struct xfs_sxi_log_format	*src_sxi_fmt;
> +	size_t				len;
> +
> +	src_sxi_fmt = buf->i_addr;
> +	len = sizeof(struct xfs_sxi_log_format);
> +
> +	if (buf->i_len == len) {
> +		memcpy(dst_sxi_fmt, src_sxi_fmt, len);
> +		return 0;
> +	}
> +	XFS_ERROR_REPORT(__func__, XFS_ERRLEVEL_LOW, NULL);
> +	return -EFSCORRUPTED;
> +}
> +
> +/*
> + * This routine is called to create an in-core extent swapext update item from
> + * the sxi format structure which was logged on disk.  It allocates an in-core
> + * sxi, copies the extents from the format structure into it, and adds the sxi
> + * to the AIL with the given LSN.
> + */
> +STATIC int
> +xlog_recover_sxi_commit_pass2(
> +	struct xlog			*log,
> +	struct list_head		*buffer_list,
> +	struct xlog_recover_item	*item,
> +	xfs_lsn_t			lsn)
> +{
> +	int				error;
> +	struct xfs_mount		*mp = log->l_mp;
> +	struct xfs_sxi_log_item		*sxi_lip;
> +	struct xfs_sxi_log_format	*sxi_formatp;
> +
> +	sxi_formatp = item->ri_buf[0].i_addr;
> +
> +	if (sxi_formatp->__pad != 0) {
> +		XFS_ERROR_REPORT(__func__, XFS_ERRLEVEL_LOW, log->l_mp);
> +		return -EFSCORRUPTED;
> +	}
> +	sxi_lip = xfs_sxi_init(mp);
> +	error = xfs_sxi_copy_format(&item->ri_buf[0], &sxi_lip->sxi_format);
> +	if (error) {
> +		xfs_sxi_item_free(sxi_lip);
> +		return error;
> +	}
> +	xfs_trans_ail_insert(log->l_ailp, &sxi_lip->sxi_item, lsn);
> +	xfs_sxi_release(sxi_lip);
> +	return 0;
> +}
> +
> +const struct xlog_recover_item_ops xlog_sxi_item_ops = {
> +	.item_type		= XFS_LI_SXI,
> +	.commit_pass2		= xlog_recover_sxi_commit_pass2,
> +};
> +
> +/*
> + * This routine is called when an SXD format structure is found in a committed
> + * transaction in the log. Its purpose is to cancel the corresponding SXI if it
> + * was still in the log. To do this it searches the AIL for the SXI with an id
> + * equal to that in the SXD format structure. If we find it we drop the SXD
> + * reference, which removes the SXI from the AIL and frees it.
> + */
> +STATIC int
> +xlog_recover_sxd_commit_pass2(
> +	struct xlog			*log,
> +	struct list_head		*buffer_list,
> +	struct xlog_recover_item	*item,
> +	xfs_lsn_t			lsn)
> +{
> +	struct xfs_sxd_log_format	*sxd_formatp;
> +
> +	sxd_formatp = item->ri_buf[0].i_addr;
> +	if (item->ri_buf[0].i_len != sizeof(struct xfs_sxd_log_format)) {
> +		XFS_ERROR_REPORT(__func__, XFS_ERRLEVEL_LOW, log->l_mp);
> +		return -EFSCORRUPTED;
> +	}
> +
> +	xlog_recover_release_intent(log, XFS_LI_SXI, sxd_formatp->sxd_sxi_id);
> +	return 0;
> +}
> +
> +const struct xlog_recover_item_ops xlog_sxd_item_ops = {
> +	.item_type		= XFS_LI_SXD,
> +	.commit_pass2		= xlog_recover_sxd_commit_pass2,
> +};
> diff --git a/fs/xfs/xfs_swapext_item.h b/fs/xfs/xfs_swapext_item.h
> new file mode 100644
> index 000000000000..7caeccdcaa81
> --- /dev/null
> +++ b/fs/xfs/xfs_swapext_item.h
> @@ -0,0 +1,61 @@
> +/* SPDX-License-Identifier: GPL-2.0-or-later */
> +/*
> + * Copyright (C) 2021 Oracle.  All Rights Reserved.
> + * Author: Darrick J. Wong <djwong@kernel.org>
> + */
> +#ifndef	__XFS_SWAPEXT_ITEM_H__
> +#define	__XFS_SWAPEXT_ITEM_H__
> +
> +/*
> + * The extent swapping intent item help us perform atomic extent swaps between
> + * two inode forks.  It does this by tracking the range of logical offsets that
> + * still need to be swapped, and relogs as progress happens.
> + *
> + * *I items should be recorded in the *first* of a series of rolled
> + * transactions, and the *D items should be recorded in the same transaction
> + * that records the associated bmbt updates.
> + *
> + * Should the system crash after the commit of the first transaction but
> + * before the commit of the final transaction in a series, log recovery will
> + * use the redo information recorded by the intent items to replay the
> + * rest of the extent swaps.
> + */
> +
> +/* kernel only SXI/SXD definitions */
> +
> +struct xfs_mount;
> +struct kmem_zone;
> +
> +/*
> + * Max number of extents in fast allocation path.
> + */
> +#define	XFS_SXI_MAX_FAST_EXTENTS	1
> +
> +/*
> + * This is the "swapext update intent" log item.  It is used to log the fact
> + * that we are swapping extents between two files.  It is used in conjunction
> + * with the "swapext update done" log item described below.
> + *
> + * These log items follow the same rules as struct xfs_efi_log_item; see the
> + * comments about that structure (in xfs_extfree_item.h) for more details.
> + */
> +struct xfs_sxi_log_item {
> +	struct xfs_log_item		sxi_item;
> +	atomic_t			sxi_refcount;
> +	struct xfs_sxi_log_format	sxi_format;
> +};
> +
> +/*
> + * This is the "swapext update done" log item.  It is used to log the fact that
> + * some extent swapping mentioned in an earlier sxi item have been performed.
> + */
> +struct xfs_sxd_log_item {
> +	struct xfs_log_item		sxd_item;
> +	struct xfs_sxi_log_item		*sxd_intent_log_item;
> +	struct xfs_sxd_log_format	sxd_format;
> +};
> +
> +extern struct kmem_zone	*xfs_sxi_zone;
> +extern struct kmem_zone	*xfs_sxd_zone;
> +
> +#endif	/* __XFS_SWAPEXT_ITEM_H__ */
>