FS needs to add the fmode capability in order to support atomic writes
during file open (refer kiocb_set_rw_flags()). Set this capability on
a regular file if ext4 can do atomic write.

Reviewed-by: John Garry <john.g.garry@oracle.com>
Signed-off-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
---
 fs/ext4/file.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/fs/ext4/file.c b/fs/ext4/file.c
index a7b9b9751a3f..8116bd78910b 100644
--- a/fs/ext4/file.c
+++ b/fs/ext4/file.c
@@ -898,6 +898,9 @@ static int ext4_file_open(struct inode *inode, struct file *filp)
 			return ret;
 	}
 
+	if (S_ISREG(inode->i_mode) && ext4_can_atomic_write(inode->i_sb))
+		filp->f_mode |= FMODE_CAN_ATOMIC_WRITE;
+
 	filp->f_mode |= FMODE_NOWAIT | FMODE_CAN_ODIRECT;
 	return dquot_file_open(inode, filp);
 }
-- 
2.46.0

On Wed, Oct 30, 2024 at 09:27:40PM +0530, Ritesh Harjani (IBM) wrote:
> FS needs to add the fmode capability in order to support atomic writes
> during file open (refer kiocb_set_rw_flags()). Set this capability on
> a regular file if ext4 can do atomic write.
> 
> Reviewed-by: John Garry <john.g.garry@oracle.com>
> Signed-off-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
> ---
>  fs/ext4/file.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/fs/ext4/file.c b/fs/ext4/file.c
> index a7b9b9751a3f..8116bd78910b 100644
> --- a/fs/ext4/file.c
> +++ b/fs/ext4/file.c
> @@ -898,6 +898,9 @@ static int ext4_file_open(struct inode *inode, struct file *filp)
>  			return ret;
>  	}
>  
> +	if (S_ISREG(inode->i_mode) && ext4_can_atomic_write(inode->i_sb))

Modulo my comment earlier about ext4_can_atomic_write, this looks ok to
me.  With either variant, I say:
Reviewed-by: Darrick J. Wong <djwong@kernel.org>

--D

> +		filp->f_mode |= FMODE_CAN_ATOMIC_WRITE;
> +
>  	filp->f_mode |= FMODE_NOWAIT | FMODE_CAN_ODIRECT;
>  	return dquot_file_open(inode, filp);
>  }
> -- 
> 2.46.0
> 
>