Re: [PATCH V7 11/19] famfs_fuse: Basic fuse kernel ABI enablement for famfs

[Dave Jiang <dave.jiang@intel.com>]

On 1/18/26 3:32 PM, John Groves wrote:
> From: John Groves <john@groves.net>
> 
> This patch starts the kernel ABI enablement of famfs in fuse.
> 
> - Kconfig: Add FUSE_FAMFS_DAX config parameter, to control
>   compilation of famfs within fuse.
> - FUSE_DAX_FMAP flag in INIT request/reply
> - fuse_conn->famfs_iomap (enable famfs-mapped files) to denote a
>   famfs-enabled connection
> 
> Reviewed-by: Joanne Koong <joannelkoong@gmail.com>
> Signed-off-by: John Groves <john@groves.net>

Reviewed-by: Dave Jiang <dave.jiang@intel.com>

> ---
>  fs/fuse/Kconfig           | 14 ++++++++++++++
>  fs/fuse/fuse_i.h          |  3 +++
>  fs/fuse/inode.c           |  6 ++++++
>  include/uapi/linux/fuse.h |  5 +++++
>  4 files changed, 28 insertions(+)
> 
> diff --git a/fs/fuse/Kconfig b/fs/fuse/Kconfig
> index 3a4ae632c94a..5ca9fae62c7b 100644
> --- a/fs/fuse/Kconfig
> +++ b/fs/fuse/Kconfig
> @@ -76,3 +76,17 @@ config FUSE_IO_URING
>  
>  	  If you want to allow fuse server/client communication through io-uring,
>  	  answer Y
> +
> +config FUSE_FAMFS_DAX
> +	bool "FUSE support for fs-dax filesystems backed by devdax"
> +	depends on FUSE_FS
> +	depends on DEV_DAX
> +	depends on FS_DAX
> +	default FUSE_FS
> +	help
> +	  This enables the fabric-attached memory file system (famfs),
> +	  which enables formatting devdax memory as a file system. Famfs
> +	  is primarily intended for scale-out shared access to
> +	  disaggregated memory.
> +
> +	  To enable famfs or other fuse/fs-dax file systems, answer Y
> diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
> index 45e108dec771..2839efb219a9 100644
> --- a/fs/fuse/fuse_i.h
> +++ b/fs/fuse/fuse_i.h
> @@ -921,6 +921,9 @@ struct fuse_conn {
>  	/* Is synchronous FUSE_INIT allowed? */
>  	unsigned int sync_init:1;
>  
> +	/* dev_dax_iomap support for famfs */
> +	unsigned int famfs_iomap:1;
> +
>  	/* Use io_uring for communication */
>  	unsigned int io_uring;
>  
> diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
> index ed667920997f..acabf92a11f8 100644
> --- a/fs/fuse/inode.c
> +++ b/fs/fuse/inode.c
> @@ -1456,6 +1456,10 @@ static void process_init_reply(struct fuse_mount *fm, struct fuse_args *args,
>  
>  			if (flags & FUSE_REQUEST_TIMEOUT)
>  				timeout = arg->request_timeout;
> +
> +			if (IS_ENABLED(CONFIG_FUSE_FAMFS_DAX) &&
> +			    flags & FUSE_DAX_FMAP)
> +				fc->famfs_iomap = 1;
>  		} else {
>  			ra_pages = fc->max_read / PAGE_SIZE;
>  			fc->no_lock = 1;
> @@ -1517,6 +1521,8 @@ static struct fuse_init_args *fuse_new_init(struct fuse_mount *fm)
>  		flags |= FUSE_SUBMOUNTS;
>  	if (IS_ENABLED(CONFIG_FUSE_PASSTHROUGH))
>  		flags |= FUSE_PASSTHROUGH;
> +	if (IS_ENABLED(CONFIG_FUSE_FAMFS_DAX))
> +		flags |= FUSE_DAX_FMAP;
>  
>  	/*
>  	 * This is just an information flag for fuse server. No need to check
> diff --git a/include/uapi/linux/fuse.h b/include/uapi/linux/fuse.h
> index c13e1f9a2f12..25686f088e6a 100644
> --- a/include/uapi/linux/fuse.h
> +++ b/include/uapi/linux/fuse.h
> @@ -240,6 +240,9 @@
>   *  - add FUSE_COPY_FILE_RANGE_64
>   *  - add struct fuse_copy_file_range_out
>   *  - add FUSE_NOTIFY_PRUNE
> + *
> + *  7.46
> + *  - Add FUSE_DAX_FMAP capability - ability to handle in-kernel fsdax maps
>   */
>  
>  #ifndef _LINUX_FUSE_H
> @@ -448,6 +451,7 @@ struct fuse_file_lock {
>   * FUSE_OVER_IO_URING: Indicate that client supports io-uring
>   * FUSE_REQUEST_TIMEOUT: kernel supports timing out requests.
>   *			 init_out.request_timeout contains the timeout (in secs)
> + * FUSE_DAX_FMAP: kernel supports dev_dax_iomap (aka famfs) fmaps
>   */
>  #define FUSE_ASYNC_READ		(1 << 0)
>  #define FUSE_POSIX_LOCKS	(1 << 1)
> @@ -495,6 +499,7 @@ struct fuse_file_lock {
>  #define FUSE_ALLOW_IDMAP	(1ULL << 40)
>  #define FUSE_OVER_IO_URING	(1ULL << 41)
>  #define FUSE_REQUEST_TIMEOUT	(1ULL << 42)
> +#define FUSE_DAX_FMAP		(1ULL << 43)
>  
>  /**
>   * CUSE INIT request/reply flags