btrfs: convert to multigrain timestamps

Enable multigrain timestamps, which should ensure that there is an
apparent change to the timestamp whenever it has been written after
being actively observed via getattr.

Beyond enabling the FS_MGTIME flag, this patch eliminates
update_time_for_write, which goes to great pains to avoid in-memory
stores. Just have it overwrite the timestamps unconditionally.

Signed-off-by: Jeff Layton <jlayton@kernel.org>
Acked-by: David Sterba <dsterba@suse.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Message-Id: <20230807-mgctime-v7-13-d1dec143a704@kernel.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>

diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index d7a9ece7a40b4da1c766f6a2b00df02188194308..b9e75c9f95acfeea57a5dea55ae5a96a9b5b78c0 100644 (file)
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -1106,25 +1106,6 @@ void btrfs_check_nocow_unlock(struct btrfs_inode *inode)
        btrfs_drew_write_unlock(&inode->root->snapshot_lock);
 }
 
-static void update_time_for_write(struct inode *inode)
-{
-       struct timespec64 now, ctime;
-
-       if (IS_NOCMTIME(inode))
-               return;
-
-       now = current_time(inode);
-       if (!timespec64_equal(&inode->i_mtime, &now))
-               inode->i_mtime = now;
-
-       ctime = inode_get_ctime(inode);
-       if (!timespec64_equal(&ctime, &now))
-               inode_set_ctime_to_ts(inode, now);
-
-       if (IS_I_VERSION(inode))
-               inode_inc_iversion(inode);
-}
-
 static int btrfs_write_check(struct kiocb *iocb, struct iov_iter *from,
                             size_t count)
 {
@@ -1156,7 +1137,10 @@ static int btrfs_write_check(struct kiocb *iocb, struct iov_iter *from,
         * need to start yet another transaction to update the inode as we will
         * update the inode when we finish writing whatever data we write.
         */
-       update_time_for_write(inode);
+       if (!IS_NOCMTIME(inode)) {
+               inode->i_mtime = inode_set_ctime_current(inode);
+               inode_inc_iversion(inode);
+       }
 
        start_pos = round_down(pos, fs_info->sectorsize);
        oldsize = i_size_read(inode);

diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index f1dd172d8d5bd75626deb8287618c1afc017fbdb..8eda51b095c9191315c791086ff5fb4a20b0d692 100644 (file)
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -2144,7 +2144,7 @@ static struct file_system_type btrfs_fs_type = {
        .name           = "btrfs",
        .mount          = btrfs_mount,
        .kill_sb        = btrfs_kill_super,
-       .fs_flags       = FS_REQUIRES_DEV | FS_BINARY_MOUNTDATA,
+       .fs_flags       = FS_REQUIRES_DEV | FS_BINARY_MOUNTDATA | FS_MGTIME,
 };
 
 static struct file_system_type btrfs_root_fs_type = {
@@ -2152,7 +2152,8 @@ static struct file_system_type btrfs_root_fs_type = {
        .name           = "btrfs",
        .mount          = btrfs_mount_root,
        .kill_sb        = btrfs_kill_super,
-       .fs_flags       = FS_REQUIRES_DEV | FS_BINARY_MOUNTDATA | FS_ALLOW_IDMAP,
+       .fs_flags       = FS_REQUIRES_DEV | FS_BINARY_MOUNTDATA |
+                         FS_ALLOW_IDMAP | FS_MGTIME,
 };
 
 MODULE_ALIAS_FS("btrfs");