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Message-Id: <20250227180813.1553404-9-john.g.garry@oracle.com>
Date: Thu, 27 Feb 2025 18:08:09 +0000
From: John Garry <john.g.garry@...cle.com>
To: brauner@...nel.org, djwong@...nel.org, cem@...nel.org
Cc: linux-xfs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
linux-kernel@...r.kernel.org, ojaswin@...ux.ibm.com,
ritesh.list@...il.com, martin.petersen@...cle.com, tytso@....edu,
linux-ext4@...r.kernel.org, John Garry <john.g.garry@...cle.com>
Subject: [PATCH v3 08/12] xfs: Iomap SW-based atomic write support
In cases of an atomic write occurs for misaligned or discontiguous disk
blocks, we will use a CoW-based method to issue the atomic write.
So, for that case, return -EAGAIN to request that the write be issued in
CoW atomic write mode. The dio write path should detect this, similar to
how misaligned regular DIO writes are handled.
For normal HW-based mode, when the range which we are atomic writing to
covers a shared data extent, try to allocate a new CoW fork. However, if
we find that what we allocated does not meet atomic write requirements
in terms of length and alignment, then fallback on the CoW-based mode
for the atomic write.
Signed-off-by: John Garry <john.g.garry@...cle.com>
---
fs/xfs/xfs_iomap.c | 143 ++++++++++++++++++++++++++++++++++++++++++++-
fs/xfs/xfs_iomap.h | 1 +
2 files changed, 142 insertions(+), 2 deletions(-)
diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c
index edfc038bf728..573108cbdc5c 100644
--- a/fs/xfs/xfs_iomap.c
+++ b/fs/xfs/xfs_iomap.c
@@ -795,6 +795,23 @@ imap_spans_range(
return true;
}
+static bool
+xfs_bmap_valid_for_atomic_write(
+ struct xfs_bmbt_irec *imap,
+ xfs_fileoff_t offset_fsb,
+ xfs_fileoff_t end_fsb)
+{
+ /* Misaligned start block wrt size */
+ if (!IS_ALIGNED(imap->br_startblock, imap->br_blockcount))
+ return false;
+
+ /* Discontiguous or mixed extents */
+ if (!imap_spans_range(imap, offset_fsb, end_fsb))
+ return false;
+
+ return true;
+}
+
static int
xfs_direct_write_iomap_begin(
struct inode *inode,
@@ -809,10 +826,13 @@ xfs_direct_write_iomap_begin(
struct xfs_bmbt_irec imap, cmap;
xfs_fileoff_t offset_fsb = XFS_B_TO_FSBT(mp, offset);
xfs_fileoff_t end_fsb = xfs_iomap_end_fsb(mp, offset, length);
+ xfs_fileoff_t orig_end_fsb = end_fsb;
+ bool atomic_hw = flags & IOMAP_ATOMIC_HW;
int nimaps = 1, error = 0;
unsigned int reflink_flags = 0;
bool shared = false;
u16 iomap_flags = 0;
+ bool needs_alloc;
unsigned int lockmode;
u64 seq;
@@ -871,13 +891,37 @@ xfs_direct_write_iomap_begin(
&lockmode, reflink_flags);
if (error)
goto out_unlock;
- if (shared)
+ if (shared) {
+ if (atomic_hw &&
+ !xfs_bmap_valid_for_atomic_write(&cmap,
+ offset_fsb, end_fsb)) {
+ error = -EAGAIN;
+ goto out_unlock;
+ }
goto out_found_cow;
+ }
end_fsb = imap.br_startoff + imap.br_blockcount;
length = XFS_FSB_TO_B(mp, end_fsb) - offset;
}
- if (imap_needs_alloc(inode, flags, &imap, nimaps))
+ needs_alloc = imap_needs_alloc(inode, flags, &imap, nimaps);
+
+ if (atomic_hw) {
+ error = -EAGAIN;
+ /*
+ * Use CoW method for when we need to alloc > 1 block,
+ * otherwise we might allocate less than what we need here and
+ * have multiple mappings.
+ */
+ if (needs_alloc && orig_end_fsb - offset_fsb > 1)
+ goto out_unlock;
+
+ if (!xfs_bmap_valid_for_atomic_write(&imap, offset_fsb,
+ orig_end_fsb))
+ goto out_unlock;
+ }
+
+ if (needs_alloc)
goto allocate_blocks;
/*
@@ -965,6 +1009,101 @@ const struct iomap_ops xfs_direct_write_iomap_ops = {
.iomap_begin = xfs_direct_write_iomap_begin,
};
+static int
+xfs_atomic_write_sw_iomap_begin(
+ struct inode *inode,
+ loff_t offset,
+ loff_t length,
+ unsigned flags,
+ struct iomap *iomap,
+ struct iomap *srcmap)
+{
+ struct xfs_inode *ip = XFS_I(inode);
+ struct xfs_mount *mp = ip->i_mount;
+ struct xfs_bmbt_irec imap, cmap;
+ xfs_fileoff_t offset_fsb = XFS_B_TO_FSBT(mp, offset);
+ xfs_fileoff_t end_fsb = xfs_iomap_end_fsb(mp, offset, length);
+ int nimaps = 1, error;
+ unsigned int reflink_flags;
+ bool shared = false;
+ u16 iomap_flags = 0;
+ unsigned int lockmode = XFS_ILOCK_EXCL;
+ u64 seq;
+
+ if (xfs_is_shutdown(mp))
+ return -EIO;
+
+ reflink_flags = XFS_REFLINK_CONVERT | XFS_REFLINK_ATOMIC_SW;
+
+ /*
+ * Set IOMAP_F_DIRTY similar to xfs_atomic_write_iomap_begin()
+ */
+ if (offset + length > i_size_read(inode))
+ iomap_flags |= IOMAP_F_DIRTY;
+
+ error = xfs_ilock_for_iomap(ip, flags, &lockmode);
+ if (error)
+ return error;
+
+ error = xfs_bmapi_read(ip, offset_fsb, end_fsb - offset_fsb, &imap,
+ &nimaps, 0);
+ if (error)
+ goto out_unlock;
+
+ error = xfs_reflink_allocate_cow(ip, &imap, &cmap, &shared,
+ &lockmode, reflink_flags);
+ /*
+ * Don't check @shared. For atomic writes, we should error when
+ * we don't get a COW mapping
+ */
+ if (error)
+ goto out_unlock;
+
+ end_fsb = imap.br_startoff + imap.br_blockcount;
+
+ length = XFS_FSB_TO_B(mp, cmap.br_startoff + cmap.br_blockcount);
+ trace_xfs_iomap_found(ip, offset, length - offset, XFS_COW_FORK, &cmap);
+ if (imap.br_startblock != HOLESTARTBLOCK) {
+ seq = xfs_iomap_inode_sequence(ip, 0);
+ error = xfs_bmbt_to_iomap(ip, srcmap, &imap, flags, 0, seq);
+ if (error)
+ goto out_unlock;
+ }
+ seq = xfs_iomap_inode_sequence(ip, IOMAP_F_SHARED);
+ xfs_iunlock(ip, lockmode);
+ return xfs_bmbt_to_iomap(ip, iomap, &cmap, flags, IOMAP_F_SHARED, seq);
+
+out_unlock:
+ if (lockmode)
+ xfs_iunlock(ip, lockmode);
+ return error;
+}
+
+static int
+xfs_atomic_write_iomap_begin(
+ struct inode *inode,
+ loff_t offset,
+ loff_t length,
+ unsigned flags,
+ struct iomap *iomap,
+ struct iomap *srcmap)
+{
+ ASSERT(flags & IOMAP_WRITE);
+ ASSERT(flags & IOMAP_DIRECT);
+
+ if (flags & IOMAP_ATOMIC_SW)
+ return xfs_atomic_write_sw_iomap_begin(inode, offset, length,
+ flags, iomap, srcmap);
+
+ ASSERT(flags & IOMAP_ATOMIC_HW);
+ return xfs_direct_write_iomap_begin(inode, offset, length, flags,
+ iomap, srcmap);
+}
+
+const struct iomap_ops xfs_atomic_write_iomap_ops = {
+ .iomap_begin = xfs_atomic_write_iomap_begin,
+};
+
static int
xfs_dax_write_iomap_end(
struct inode *inode,
diff --git a/fs/xfs/xfs_iomap.h b/fs/xfs/xfs_iomap.h
index 8347268af727..b7fbbc909943 100644
--- a/fs/xfs/xfs_iomap.h
+++ b/fs/xfs/xfs_iomap.h
@@ -53,5 +53,6 @@ extern const struct iomap_ops xfs_read_iomap_ops;
extern const struct iomap_ops xfs_seek_iomap_ops;
extern const struct iomap_ops xfs_xattr_iomap_ops;
extern const struct iomap_ops xfs_dax_write_iomap_ops;
+extern const struct iomap_ops xfs_atomic_write_iomap_ops;
#endif /* __XFS_IOMAP_H__*/
--
2.31.1
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