[PATCH 01/10] fs: turn inode ctime fields into a single ktime_t

Jeff Layton
2024-06-27T01:00:36Z

The ctime is not settable to arbitrary values. It always comes from the
system clock, so we'll never stamp an inode with a value that can't be
represented there. If we disregard people setting their system clock
past the year 2262, there is no reason we can't replace the ctime fields
with a ktime_t.

Switch the ctime fields to a single ktime_t. Move the i_generation down
above i_fsnotify_mask and then move the i_version into the resulting 8
byte hole. This shrinks struct inode by 8 bytes total, and should
improve the cache footprint as the i_version and ctime are usually
updated together.

The one downside I can see to switching to a ktime_t is that if someone
has a filesystem with files on it that has ctimes outside the ktime_t
range (before ~1678 AD or after ~2262 AD), we won't be able to display
them properly in stat() without some special treatment in the
filesystem. The operating assumption here is that that is not a
practical problem.

Signed-off-by: Jeff Layton <jlayton@kernel.org>
---
include/linux/fs.h | 26 +++++++++++---------------
1 file changed, 11 insertions(+), 15 deletions(-)

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 5ff362277834..5139dec085f2 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -662,11 +662,10 @@ struct inode {
loff_t i_size;
time64_t i_atime_sec;
time64_t i_mtime_sec;
- time64_t i_ctime_sec;
u32 i_atime_nsec;
u32 i_mtime_nsec;
- u32 i_ctime_nsec;
- u32 i_generation;
+ ktime_t __i_ctime;
+ atomic64_t i_version;
spinlock_t i_lock; /* i_blocks, i_bytes, maybe i_size */
unsigned short i_bytes;
u8 i_blkbits;
@@ -701,7 +700,6 @@ struct inode {
struct hlist_head i_dentry;
struct rcu_head i_rcu;
};
- atomic64_t i_version;
atomic64_t i_sequence; /* see futex */
atomic_t i_count;
atomic_t i_dio_count;
@@ -724,6 +722,8 @@ struct inode {
};

+ u32 i_generation;
+
#ifdef CONFIG_FSNOTIFY
__u32 i_fsnotify_mask; /* all events this inode cares about */
/* 32-bit hole reserved for expanding i_fsnotify_mask */
@@ -1608,29 +1608,25 @@ static inline struct timespec64 inode_set_mtime(struct inode *inode,
return inode_set_mtime_to_ts(inode, ts);
}

-static inline time64_t inode_get_ctime_sec(const struct inode *inode)
+static inline struct timespec64 inode_get_ctime(const struct inode *inode)
{
- return inode->i_ctime_sec;
+ return ktime_to_timespec64(inode->__i_ctime);
}

-static inline long inode_get_ctime_nsec(const struct inode *inode)
+static inline time64_t inode_get_ctime_sec(const struct inode *inode)
{
- return inode->i_ctime_nsec;
+ return inode_get_ctime(inode).tv_sec;
}

-static inline struct timespec64 inode_get_ctime(const struct inode *inode)
+static inline long inode_get_ctime_nsec(const struct inode *inode)
{
- struct timespec64 ts = { .tv_sec = inode_get_ctime_sec(inode),
- .tv_nsec = inode_get_ctime_nsec(inode) };
-
- return ts;
+ return inode_get_ctime(inode).tv_nsec;
}

static inline struct timespec64 inode_set_ctime_to_ts(struct inode *inode,
struct timespec64 ts)
{
- inode->i_ctime_sec = ts.tv_sec;
- inode->i_ctime_nsec = ts.tv_nsec;
+ inode->__i_ctime = ktime_set(ts.tv_sec, ts.tv_nsec);
return ts;
}

--
2.45.2