[PATCH 11/14] fs: add a ->sync_lazytime method

Christoph Hellwig
2025-11-14T06:28:12Z

Allow the file system to explicitly implement lazytime syncing instead
of pigging back on generic inode dirtying. This allows to simplify
the XFS implementation and prepares for non-blocking lazytime timestamp
updates.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
Documentation/filesystems/locking.rst | 2 ++
Documentation/filesystems/vfs.rst | 6 ++++++
fs/fs-writeback.c | 13 +++++++++++--
include/linux/fs.h | 1 +
4 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/Documentation/filesystems/locking.rst b/Documentation/filesystems/locking.rst
index 77704fde9845..9b2f14ada8cd 100644
--- a/Documentation/filesystems/locking.rst
+++ b/Documentation/filesystems/locking.rst
@@ -81,6 +81,7 @@ prototypes::
ssize_t (*listxattr) (struct dentry *, char *, size_t);
int (*fiemap)(struct inode *, struct fiemap_extent_info *, u64 start, u64 len);
void (*update_time)(struct inode *, struct timespec *, int);
+ void (*sync_lazytime)(struct inode *inode);
int (*atomic_open)(struct inode *, struct dentry *,
struct file *, unsigned open_flag,
umode_t create_mode);
@@ -117,6 +118,7 @@ getattr: no
listxattr: no
fiemap: no
update_time: no
+sync_lazytime: no
atomic_open: shared (exclusive if O_CREAT is set in open flags)
tmpfile: no
fileattr_get: no or exclusive
diff --git a/Documentation/filesystems/vfs.rst b/Documentation/filesystems/vfs.rst
index 4f13b01e42eb..ff59760daae2 100644
--- a/Documentation/filesystems/vfs.rst
+++ b/Documentation/filesystems/vfs.rst
@@ -486,6 +486,7 @@ As of kernel 2.6.22, the following members are defined:
int (*getattr) (struct mnt_idmap *, const struct path *, struct kstat *, u32, unsigned int);
ssize_t (*listxattr) (struct dentry *, char *, size_t);
void (*update_time)(struct inode *, struct timespec *, int);
+ void (*sync_lazytime)(struct inode *inode);
int (*atomic_open)(struct inode *, struct dentry *, struct file *,
unsigned open_flag, umode_t create_mode);
int (*tmpfile) (struct mnt_idmap *, struct inode *, struct file *, umode_t);
@@ -642,6 +643,11 @@ otherwise noted.
an inode. If this is not defined the VFS will update the inode
itself and call mark_inode_dirty_sync.

+``sync_lazytime``:
+ called by the writeback code to update the lazy time stamps to
+ regular time stamp updates that get syncing into the on-disk
+ inode.
+
``atomic_open``
called on the last component of an open. Using this optional
method the filesystem can look up, possibly create and open the
diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index ae6d1f1ccc71..7245f547416f 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -1699,7 +1699,10 @@ bool sync_lazytime(struct inode *inode)
return false;

trace_writeback_lazytime(inode);
- mark_inode_dirty_sync(inode);
+ if (inode->i_op->sync_lazytime)
+ inode->i_op->sync_lazytime(inode);
+ else
+ mark_inode_dirty_sync(inode);
return false;
}

@@ -2547,6 +2550,8 @@ void __mark_inode_dirty(struct inode *inode, int flags)
trace_writeback_mark_inode_dirty(inode, flags);

if (flags & I_DIRTY_INODE) {
+ bool was_dirty_time = true;
+
/*
* Inode timestamp update will piggback on this dirtying.
* We tell ->dirty_inode callback that timestamps need to
@@ -2557,6 +2562,7 @@ void __mark_inode_dirty(struct inode *inode, int flags)
if (inode->i_state & I_DIRTY_TIME) {
inode->i_state &= ~I_DIRTY_TIME;
flags |= I_DIRTY_TIME;
+ was_dirty_time = true;
}
spin_unlock(&inode->i_lock);
}
@@ -2569,9 +2575,12 @@ void __mark_inode_dirty(struct inode *inode, int flags)
* for just I_DIRTY_PAGES or I_DIRTY_TIME.
*/
trace_writeback_dirty_inode_start(inode, flags);
- if (sb->s_op->dirty_inode)
+ if (sb->s_op->dirty_inode) {
sb->s_op->dirty_inode(inode,
flags & (I_DIRTY_INODE | I_DIRTY_TIME));
+ } else if (was_dirty_time && inode->i_op->sync_lazytime) {
+ inode->i_op->sync_lazytime(inode);
+ }
trace_writeback_dirty_inode(inode, flags);

/* I_DIRTY_INODE supersedes I_DIRTY_TIME. */
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 5c762d80b8a8..61051c86dbd2 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2363,6 +2363,7 @@ struct inode_operations {
int (*fiemap)(struct inode *, struct fiemap_extent_info *, u64 start,
u64 len);
int (*update_time)(struct inode *, int);
+ void (*sync_lazytime)(struct inode *inode);
int (*atomic_open)(struct inode *, struct dentry *,
struct file *, unsigned open_flag,
umode_t create_mode);
--
2.47.3