Re: [PATCH v4 1/3] libfs: Add directory operations for stable offsets

[Christoph Hellwig <hch@infradead.org>]

> + * @dir: parent directory to be initialized
> + *
> + */
> +void stable_offset_init(struct inode *dir)
> +{
> +	xa_init_flags(&dir->i_doff_map, XA_FLAGS_ALLOC1);
> +	dir->i_next_offset = 0;
> +}
> +EXPORT_SYMBOL(stable_offset_init);

If this is exported I'd much prefer a EXPORT_SYMBOL_GPL.  But the only
user so far is shmfs, which can't be modular anyway, so I think we can
drop the exports.

> --- a/include/linux/dcache.h
> +++ b/include/linux/dcache.h
> @@ -96,6 +96,7 @@ struct dentry {
>  	struct super_block *d_sb;	/* The root of the dentry tree */
>  	unsigned long d_time;		/* used by d_revalidate */
>  	void *d_fsdata;			/* fs-specific data */
> +	u32 d_offset;			/* directory offset in parent */
>  
>  	union {
>  		struct list_head d_lru;		/* LRU list */
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 133f0640fb24..3fc2c04ed8ff 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -719,6 +719,10 @@ struct inode {
>  #endif
>  
>  	void			*i_private; /* fs or device private pointer */
> +
> +	/* simplefs stable directory offset tracking */
> +	struct xarray		i_doff_map;
> +	u32			i_next_offset;

We can't just increase the size of the dentry and inode for everyone
for something that doesn't make any sense for normal file systems.
This needs to move out into structures allocated by the file system
and embedded into or used as the private dentry/inode data.

> +extern void stable_offset_init(struct inode *dir);
> +extern int stable_offset_add(struct inode *dir, struct dentry *dentry);
> +extern void stable_offset_remove(struct inode *dir, struct dentry *dentry);
> +extern void stable_offset_destroy(struct inode *dir);

Please drop all the pointless externs for function prototypes.