Re: [PATCH 05/11] vfs: add RENAME_NOREPLACE flag

[J. Bruce Fields]

On Wed, Jan 08, 2014 at 11:10:09PM +0100, Miklos Szeredi wrote:
> From: Miklos Szeredi <mszeredi@xxxxxxx>
> 
> If this flag is specified and the target of the rename exists then the
> rename syscall fails with EEXIST.

Why is this useful?

(I'm sure it is, it'd just be useful to have the reasons recorded
someplace.)

> The VFS does the existence checking, so it is trivial to enable for most
> local filesystems.  This patch only enables it in ext4.
> 
> For network filesystems the VFS check is not enough as there may be a race
> between a remote create and the rename, so these filesystems need to handle
> this flag in their ->rename() implementations to ensure atomicity.

Till that's done this should probably result in -EOPNOTSUPP on those
filesystems?

I think this would need new protocol in the NFS case.

--b.

> 
> Suggested-by: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
> Signed-off-by: Miklos Szeredi <mszeredi@xxxxxxx>
> ---
>  fs/ext4/namei.c         |  2 +-
>  fs/namei.c              | 21 +++++++++++++--------
>  include/uapi/linux/fs.h |  2 ++
>  3 files changed, 16 insertions(+), 9 deletions(-)
> 
> diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
> index 08c40f4e7eed..e0129b6e74cf 100644
> --- a/fs/ext4/namei.c
> +++ b/fs/ext4/namei.c
> @@ -3021,7 +3021,7 @@ static int ext4_rename(struct inode *old_dir, struct dentry *old_dentry,
>  	int inlined = 0, new_inlined = 0;
>  	struct ext4_dir_entry_2 *parent_de;
>  
> -	if (flags)
> +	if (flags & ~RENAME_NOREPLACE)
>  		return -EOPNOTSUPP;
>  
>  	dquot_initialize(old_dir);
> diff --git a/fs/namei.c b/fs/namei.c
> index 593673fcbfef..f9cf3020394c 100644
> --- a/fs/namei.c
> +++ b/fs/namei.c
> @@ -4123,7 +4123,7 @@ SYSCALL_DEFINE5(renameat2, int, olddfd, const char __user *, oldname,
>  	bool should_retry = false;
>  	int error;
>  
> -	if (flags)
> +	if (flags & ~RENAME_NOREPLACE)
>  		return -EOPNOTSUPP;
>  
>  retry:
> @@ -4149,6 +4149,8 @@ retry:
>  		goto exit2;
>  
>  	new_dir = newnd.path.dentry;
> +	if (flags & RENAME_NOREPLACE)
> +		error = -EEXIST;
>  	if (newnd.last_type != LAST_NORM)
>  		goto exit2;
>  
> @@ -4171,22 +4173,25 @@ retry_deleg:
>  	error = -ENOENT;
>  	if (d_is_negative(old_dentry))
>  		goto exit4;
> +	new_dentry = lookup_hash(&newnd);
> +	error = PTR_ERR(new_dentry);
> +	if (IS_ERR(new_dentry))
> +		goto exit4;
> +	error = -EEXIST;
> +	if ((flags & RENAME_NOREPLACE) && d_is_positive(new_dentry))
> +		goto exit5;
>  	/* unless the source is a directory trailing slashes give -ENOTDIR */
>  	if (!d_is_dir(old_dentry)) {
>  		error = -ENOTDIR;
>  		if (oldnd.last.name[oldnd.last.len])
> -			goto exit4;
> +			goto exit5;
>  		if (newnd.last.name[newnd.last.len])
> -			goto exit4;
> +			goto exit5;
>  	}
>  	/* source should not be ancestor of target */
>  	error = -EINVAL;
>  	if (old_dentry == trap)
> -		goto exit4;
> -	new_dentry = lookup_hash(&newnd);
> -	error = PTR_ERR(new_dentry);
> -	if (IS_ERR(new_dentry))
> -		goto exit4;
> +		goto exit5;
>  	/* target should not be an ancestor of source */
>  	error = -ENOTEMPTY;
>  	if (new_dentry == trap)
> diff --git a/include/uapi/linux/fs.h b/include/uapi/linux/fs.h
> index 6c28b61bb690..9250f4dd7d96 100644
> --- a/include/uapi/linux/fs.h
> +++ b/include/uapi/linux/fs.h
> @@ -35,6 +35,8 @@
>  #define SEEK_HOLE	4	/* seek to the next hole */
>  #define SEEK_MAX	SEEK_HOLE
>  
> +#define RENAME_NOREPLACE	(1 << 0)	/* Don't overwrite target */
> +
>  struct fstrim_range {
>  	__u64 start;
>  	__u64 len;
> -- 
> 1.8.1.4
> 
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