[PATCH RFC 07/10] xfs: Add xfs_file_dio_write_atomic()

John Garry
2025-02-04T12:04:14Z

Add xfs_file_dio_write_atomic() for dedicated handling of atomic writes.

In case of -EAGAIN being returned from iomap_dio_rw(), reissue the write
in CoW-based atomic write mode.

In the CoW-based atomic write mode, first unshare blocks so that we don't
have a cow fork for the data in the range which we are writing.

Signed-off-by: John Garry <john.g.garry@oracle.com>
---
fs/xfs/xfs_file.c | 51 +++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 51 insertions(+)

diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index fd05b66aea3f..12af5cdc3094 100644
--- a/fs/xfs/xfs_file.c
+++ b/fs/xfs/xfs_file.c
@@ -619,6 +619,55 @@ xfs_file_dio_write_aligned(
return ret;
}

+static noinline ssize_t
+xfs_file_dio_write_atomic(
+ struct xfs_inode *ip,
+ struct kiocb *iocb,
+ struct iov_iter *from)
+{
+ unsigned int iolock = XFS_IOLOCK_SHARED;
+ bool use_cow = false;
+ unsigned int dio_flags;
+ ssize_t ret;
+
+retry:
+ ret = xfs_ilock_iocb_for_write(iocb, &iolock);
+ if (ret)
+ return ret;
+
+ ret = xfs_file_write_checks(iocb, from, &iolock);
+ if (ret)
+ goto out_unlock;
+
+ if (use_cow) {
+ ret = xfs_reflink_unshare(ip, iocb->ki_pos,
+ iov_iter_count(from));
+ if (ret)
+ goto out_unlock;
+ }
+
+ trace_xfs_file_direct_write(iocb, from);
+ if (use_cow)
+ dio_flags = IOMAP_DIO_ATOMIC_COW;
+ else
+ dio_flags = 0;
+
+ ret = iomap_dio_rw(iocb, from, &xfs_direct_write_iomap_ops,
+ &xfs_dio_write_ops, dio_flags, NULL, 0);
+
+ if (ret == -EAGAIN && !(iocb->ki_flags & IOCB_NOWAIT) && !use_cow) {
+ xfs_iunlock(ip, iolock);
+ iolock = XFS_IOLOCK_EXCL;
+ use_cow = true;
+ goto retry;
+ }
+
+out_unlock:
+ if (iolock)
+ xfs_iunlock(ip, iolock);
+ return ret;
+}
+
/*
* Handle block unaligned direct I/O writes
*
@@ -723,6 +772,8 @@ xfs_file_dio_write(
return -EINVAL;
if ((iocb->ki_pos | count) & ip->i_mount->m_blockmask)
return xfs_file_dio_write_unaligned(ip, iocb, from);
+ if (iocb->ki_flags & IOCB_ATOMIC)
+ return xfs_file_dio_write_atomic(ip, iocb, from);
return xfs_file_dio_write_aligned(ip, iocb, from);
}

--
2.31.1