Re: [Virtio-fs] [PATCH v8 5/7] fuse: negotiate per inode DAX in FUSE_INIT

[Vivek Goyal <vgoyal@redhat.com>]

On Thu, Nov 25, 2021 at 03:05:28PM +0800, Jeffle Xu wrote:
> Among the FUSE_INIT phase, client shall advertise per inode DAX if it's
> mounted with "dax=inode". Then server is aware that client is in per
> inode DAX mode, and will construct per-inode DAX attribute accordingly.
> 
> Server shall also advertise support for per inode DAX. If server doesn't
> support it while client is mounted with "dax=inode", client will
> silently fallback to "dax=never" since "dax=inode" is advisory only.
> 
> Signed-off-by: Jeffle Xu <jefflexu@linux.alibaba.com>

Reviewed-by: Vivek Goyal <vgoyal@redhat.com>

Vivek
> ---
>  fs/fuse/dax.c    |  2 +-
>  fs/fuse/fuse_i.h |  3 +++
>  fs/fuse/inode.c  | 13 +++++++++----
>  3 files changed, 13 insertions(+), 5 deletions(-)
> 
> diff --git a/fs/fuse/dax.c b/fs/fuse/dax.c
> index 1550c3624414..234c2278420f 100644
> --- a/fs/fuse/dax.c
> +++ b/fs/fuse/dax.c
> @@ -1351,7 +1351,7 @@ static bool fuse_should_enable_dax(struct inode *inode, unsigned int flags)
>  		return true;
>  
>  	/* dax_mode is FUSE_DAX_INODE* */
> -	return flags & FUSE_ATTR_DAX;
> +	return fc->inode_dax && (flags & FUSE_ATTR_DAX);
>  }
>  
>  void fuse_dax_inode_init(struct inode *inode, unsigned int flags)
> diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
> index f03ea7cb74b0..83970723314a 100644
> --- a/fs/fuse/fuse_i.h
> +++ b/fs/fuse/fuse_i.h
> @@ -777,6 +777,9 @@ struct fuse_conn {
>  	/* Propagate syncfs() to server */
>  	unsigned int sync_fs:1;
>  
> +	/* Does the filesystem support per inode DAX? */
> +	unsigned int inode_dax:1;
> +
>  	/** The number of requests waiting for completion */
>  	atomic_t num_waiting;
>  
> diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
> index 0669e41a9645..b26612fce6d0 100644
> --- a/fs/fuse/inode.c
> +++ b/fs/fuse/inode.c
> @@ -1169,10 +1169,13 @@ static void process_init_reply(struct fuse_mount *fm, struct fuse_args *args,
>  					min_t(unsigned int, fc->max_pages_limit,
>  					max_t(unsigned int, arg->max_pages, 1));
>  			}
> -			if (IS_ENABLED(CONFIG_FUSE_DAX) &&
> -			    arg->flags & FUSE_MAP_ALIGNMENT &&
> -			    !fuse_dax_check_alignment(fc, arg->map_alignment)) {
> -				ok = false;
> +			if (IS_ENABLED(CONFIG_FUSE_DAX)) {
> +				if (arg->flags & FUSE_MAP_ALIGNMENT &&
> +				    !fuse_dax_check_alignment(fc, arg->map_alignment)) {
> +					ok = false;
> +				}
> +				if (arg->flags & FUSE_HAS_INODE_DAX)
> +					fc->inode_dax = 1;
>  			}
>  			if (arg->flags & FUSE_HANDLE_KILLPRIV_V2) {
>  				fc->handle_killpriv_v2 = 1;
> @@ -1227,6 +1230,8 @@ void fuse_send_init(struct fuse_mount *fm)
>  #ifdef CONFIG_FUSE_DAX
>  	if (fm->fc->dax)
>  		ia->in.flags |= FUSE_MAP_ALIGNMENT;
> +	if (fuse_is_inode_dax_mode(fm->fc->dax_mode))
> +		ia->in.flags |= FUSE_HAS_INODE_DAX;
>  #endif
>  	if (fm->fc->auto_submounts)
>  		ia->in.flags |= FUSE_SUBMOUNTS;
> -- 
> 2.27.0
>