[PATCH 18/25] xfs: allow xfs_swap_range to use older extent swap algorithms

Darrick J. Wong
2023-12-31T20:28:56Z

If userspace permits non-atomic swap operations, use the older code
paths to implement the same functionality.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
---
fs/xfs/xfs_bmap_util.c | 4 +-
fs/xfs/xfs_bmap_util.h | 4 ++
fs/xfs/xfs_xchgrange.c | 123 ++++++++++++++++++++++++++++++++++++++++++++----
3 files changed, 118 insertions(+), 13 deletions(-)

diff --git a/fs/xfs/xfs_bmap_util.c b/fs/xfs/xfs_bmap_util.c
index c6d8d061c998b..405d02e71ab65 100644
--- a/fs/xfs/xfs_bmap_util.c
+++ b/fs/xfs/xfs_bmap_util.c
@@ -1255,7 +1255,7 @@ xfs_insert_file_space(
* reject and log the attempt. basically we are putting the responsibility on
* userspace to get this right.
*/
-static int
+int
xfs_swap_extents_check_format(
struct xfs_inode *ip, /* target inode */
struct xfs_inode *tip) /* tmp inode */
@@ -1397,7 +1397,7 @@ xfs_swap_change_owner(
}

/* Swap the extents of two files by swapping data forks. */
-STATIC int
+int
xfs_swap_extent_forks(
struct xfs_trans **tpp,
struct xfs_swapext_req *req)
diff --git a/fs/xfs/xfs_bmap_util.h b/fs/xfs/xfs_bmap_util.h
index 6888078f5c31e..39c71da08403c 100644
--- a/fs/xfs/xfs_bmap_util.h
+++ b/fs/xfs/xfs_bmap_util.h
@@ -69,6 +69,10 @@ int xfs_free_eofblocks(struct xfs_inode *ip);
int xfs_swap_extents(struct xfs_inode *ip, struct xfs_inode *tip,
struct xfs_swapext *sx);

+struct xfs_swapext_req;
+int xfs_swap_extent_forks(struct xfs_trans **tpp, struct xfs_swapext_req *req);
+int xfs_swap_extents_check_format(struct xfs_inode *ip, struct xfs_inode *tip);
+
xfs_daddr_t xfs_fsb_to_db(struct xfs_inode *ip, xfs_fsblock_t fsb);

xfs_extnum_t xfs_bmap_count_leaves(struct xfs_ifork *ifp, xfs_filblks_t *count);
diff --git a/fs/xfs/xfs_xchgrange.c b/fs/xfs/xfs_xchgrange.c
index 835e83c90f7f5..328217551c1e8 100644
--- a/fs/xfs/xfs_xchgrange.c
+++ b/fs/xfs/xfs_xchgrange.c
@@ -712,6 +712,65 @@ xfs_xchg_range_rele_log_assist(
xlog_drop_incompat_feat(mp->m_log, XLOG_INCOMPAT_FEAT_SWAPEXT);
}

+/*
+ * Can we use xfs_swapext() to perform the exchange?
+ *
+ * The swapext state tracking mechanism uses deferred bmap log intent (BUI)
+ * items to swap extents between file forks, and it /can/ track the overall
+ * operation status over a file range using swapext log intent (SXI) items.
+ */
+static inline bool
+xfs_xchg_use_swapext(
+ struct xfs_mount *mp,
+ unsigned int xchg_flags)
+{
+ /*
+ * If the caller got permission from the log to use SXI items, we will
+ * use xfs_swapext with both log items.
+ */
+ if (xchg_flags & XFS_XCHG_RANGE_LOGGED)
+ return true;
+
+ /*
+ * If the caller didn't get permission to use SXI items, then userspace
+ * must have allowed non-atomic swap mode. Use the state tracking in
+ * xfs_swapext to log BUI log items if the fs supports rmap or reflink.
+ */
+ return xfs_swapext_supports_nonatomic(mp);
+}
+
+/*
+ * Can we use the old data fork swapping to perform the exchange?
+ *
+ * Userspace must be asking for a full swap of two files with the same file
+ * size and cannot require atomic mode.
+ */
+static inline bool
+xfs_xchg_use_forkswap(
+ const struct xfs_exch_range *fxr,
+ struct xfs_inode *ip1,
+ struct xfs_inode *ip2)
+{
+ if (!(fxr->flags & XFS_EXCH_RANGE_NONATOMIC))
+ return false;
+ if (!(fxr->flags & XFS_EXCH_RANGE_FULL_FILES))
+ return false;
+ if (fxr->flags & XFS_EXCH_RANGE_TO_EOF)
+ return false;
+ if (fxr->file1_offset != 0 || fxr->file2_offset != 0)
+ return false;
+ if (fxr->length != ip1->i_disk_size)
+ return false;
+ if (fxr->length != ip2->i_disk_size)
+ return false;
+ return true;
+}
+
+enum xchg_strategy {
+ SWAPEXT = 1, /* xfs_swapext() */
+ FORKSWAP = 2, /* exchange forks */
+};
+
/* Exchange the contents of two files. */
int
xfs_xchg_range(
@@ -731,20 +790,13 @@ xfs_xchg_range(
};
struct xfs_trans *tp;
unsigned int qretry;
+ unsigned int flags = 0;
bool retried = false;
+ enum xchg_strategy strategy;
int error;

trace_xfs_xchg_range(ip1, fxr, ip2, xchg_flags);

- /*
- * This function only supports using log intent items (SXI items if
- * atomic exchange is required, or BUI items if not) to exchange file
- * data. The legacy whole-fork swap will be ported in a later patch.
- */
- if (!(xchg_flags & XFS_XCHG_RANGE_LOGGED) &&
- !xfs_swapext_supports_nonatomic(mp))
- return -EOPNOTSUPP;
-
if (fxr->flags & XFS_EXCH_RANGE_TO_EOF)
req.req_flags |= XFS_SWAP_REQ_SET_SIZES;
if (fxr->flags & XFS_EXCH_RANGE_FILE1_WRITTEN)
@@ -756,10 +808,25 @@ xfs_xchg_range(
if (error)
return error;

+ /*
+ * We haven't decided which exchange strategy we want to use yet, but
+ * here we must choose if we want freed blocks during the swap to be
+ * added to the transaction block reservation (RES_FDBLKS) or freed
+ * into the global fdblocks. The legacy fork swap mechanism doesn't
+ * free any blocks, so it doesn't require it. It is also the only
+ * option that works for older filesystems.
+ *
+ * The bmap log intent items that were added with rmap and reflink can
+ * change the bmbt shape, so the intent-based swap strategies require
+ * us to set RES_FDBLKS.
+ */
+ if (xfs_has_lazysbcount(mp))
+ flags |= XFS_TRANS_RES_FDBLKS;
+
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);
+ flags, &tp);
if (error)
return error;

@@ -802,6 +869,30 @@ xfs_xchg_range(
if (error)
goto out_trans_cancel;

+ if (xfs_xchg_use_swapext(mp, xchg_flags)) {
+ /* Exchange the file contents with our fancy state tracking. */
+ strategy = SWAPEXT;
+ } else if (xfs_xchg_use_forkswap(fxr, ip1, ip2)) {
+ /*
+ * Exchange the file contents by using the old bmap fork
+ * exchange code, if we're a defrag tool doing a full file
+ * swap.
+ */
+ strategy = FORKSWAP;
+
+ error = xfs_swap_extents_check_format(ip2, ip1);
+ if (error) {
+ xfs_notice(mp,
+ "%s: inode 0x%llx format is incompatible for exchanging.",
+ __func__, ip2->i_ino);
+ goto out_trans_cancel;
+ }
+ } else {
+ /* We cannot exchange the file contents. */
+ error = -EOPNOTSUPP;
+ goto out_trans_cancel;
+ }
+
/* If we got this far on a dry run, all parameters are ok. */
if (fxr->flags & XFS_EXCH_RANGE_DRY_RUN)
goto out_trans_cancel;
@@ -814,7 +905,17 @@ xfs_xchg_range(
xfs_trans_ichgtime(tp, ip2,
XFS_ICHGTIME_MOD | XFS_ICHGTIME_CHG);

- xfs_swapext(tp, &req);
+ switch (strategy) {
+ case SWAPEXT:
+ xfs_swapext(tp, &req);
+ error = 0;
+ break;
+ case FORKSWAP:
+ error = xfs_swap_extent_forks(&tp, &req);
+ break;
+ }
+ if (error)
+ goto out_trans_cancel;

/*
* Force the log to persist metadata updates if the caller or the