Re: [PATCH 32/33] fuse: enable swapfile activation on iomap

["Darrick J. Wong" <djwong@kernel.org>]

On Wed, Apr 29, 2026 at 07:32:02AM -0700, Darrick J. Wong wrote:
> From: Darrick J. Wong <djwong@kernel.org>
> 
> It turns out that fuse supports swapfile activation, so let's enable
> that.
> 
> Signed-off-by: "Darrick J. Wong" <djwong@kernel.org>
> ---
>  fs/fuse/fuse_trace.h      |    1 +
>  include/uapi/linux/fuse.h |    5 ++++
>  fs/fuse/fuse_iomap.c      |   54 ++++++++++++++++++++++++++++++++++++++++++++-
>  3 files changed, 59 insertions(+), 1 deletion(-)
> 
> 
> diff --git a/fs/fuse/fuse_trace.h b/fs/fuse/fuse_trace.h
> index de7d483d4b0f34..63cc1496ee5ca1 100644
> --- a/fs/fuse/fuse_trace.h
> +++ b/fs/fuse/fuse_trace.h
> @@ -300,6 +300,7 @@ struct iomap;
>  	{ FUSE_IOMAP_OP_DAX,			"fsdax" }, \
>  	{ FUSE_IOMAP_OP_ATOMIC,			"atomic" }, \
>  	{ FUSE_IOMAP_OP_DONTCACHE,		"dontcache" }, \
> +	{ FUSE_IOMAP_OP_SWAPFILE,		"swapfile" }, \
>  	{ FUSE_IOMAP_OP_WRITEBACK,		"writeback" }
>  
>  #define FUSE_IOMAP_TYPE_STRINGS \
> diff --git a/include/uapi/linux/fuse.h b/include/uapi/linux/fuse.h
> index 9e59fba64f48d9..5f3724f36f764a 100644
> --- a/include/uapi/linux/fuse.h
> +++ b/include/uapi/linux/fuse.h
> @@ -1406,6 +1406,9 @@ struct fuse_uring_cmd_req {
>  #define FUSE_IOMAP_OP_ATOMIC		(1U << 9)
>  #define FUSE_IOMAP_OP_DONTCACHE		(1U << 10)
>  
> +/* swapfile config operation */
> +#define FUSE_IOMAP_OP_SWAPFILE		(1U << 30)
> +
>  /* pagecache writeback operation */
>  #define FUSE_IOMAP_OP_WRITEBACK		(1U << 31)
>  
> @@ -1460,6 +1463,8 @@ struct fuse_iomap_end_in {
>  #define FUSE_IOMAP_IOEND_APPEND		(1U << 4)
>  /* is pagecache writeback */
>  #define FUSE_IOMAP_IOEND_WRITEBACK	(1U << 5)
> +/* swapfile deactivation */
> +#define FUSE_IOMAP_IOEND_SWAPOFF	(1U << 6)
>  
>  struct fuse_iomap_ioend_in {
>  	uint32_t flags;		/* FUSE_IOMAP_IOEND_* */
> diff --git a/fs/fuse/fuse_iomap.c b/fs/fuse/fuse_iomap.c
> index 1e01e0011a412d..cf52e2747e7f7f 100644
> --- a/fs/fuse/fuse_iomap.c
> +++ b/fs/fuse/fuse_iomap.c
> @@ -8,6 +8,7 @@
>  #include <linux/pagemap.h>
>  #include <linux/falloc.h>
>  #include <linux/fadvise.h>
> +#include <linux/swap.h>
>  #include "fuse_i.h"
>  #include "fuse_trace.h"
>  #include "fuse_iomap.h"
> @@ -202,13 +203,16 @@ static inline uint16_t fuse_iomap_flags_from_server(uint16_t fuse_f_flags)
>  #undef XMAP2
>  #undef XMAP
>  
> +#define FUSE_IOMAP_PRIVATE_OPS	(FUSE_IOMAP_OP_WRITEBACK | \
> +				 FUSE_IOMAP_OP_SWAPFILE)
> +
>  /* Convert IOMAP_* operation flags to FUSE_IOMAP_OP_* */
>  #define XMAP(word) \
>  	if (iomap_op_flags & IOMAP_##word) \
>  		ret |= FUSE_IOMAP_OP_##word
>  static inline uint32_t fuse_iomap_op_to_server(unsigned iomap_op_flags)
>  {
> -	uint32_t ret = iomap_op_flags & FUSE_IOMAP_OP_WRITEBACK;
> +	uint32_t ret = iomap_op_flags & FUSE_IOMAP_PRIVATE_OPS;
>  
>  	XMAP(WRITE);
>  	XMAP(ZERO);
> @@ -757,6 +761,13 @@ fuse_should_send_iomap_ioend(const struct fuse_mount *fm,
>  	if (inarg->error)
>  		return true;
>  
> +	/*
> +	 * Always send an ioend for swapoff to let the fuse server know the
> +	 * long term layout "lease" is over.
> +	 */
> +	if (inarg->flags & FUSE_IOMAP_IOEND_SWAPOFF)
> +		return true;
> +
>  	/* Send an ioend if we performed an IO involving metadata changes. */
>  	return inarg->written > 0 &&
>  	       (inarg->flags & (FUSE_IOMAP_IOEND_SHARED |
> @@ -1801,6 +1812,43 @@ static void fuse_iomap_readahead(struct readahead_control *rac)
>  	iomap_bio_readahead(rac, &fuse_iomap_ops);
>  }
>  
> +#ifdef CONFIG_SWAP
> +static int fuse_iomap_swapfile_begin(struct inode *inode, loff_t pos,
> +				     loff_t count, unsigned opflags,
> +				     struct iomap *iomap, struct iomap *srcmap)
> +{
> +	return fuse_iomap_begin(inode, pos, count,
> +				FUSE_IOMAP_OP_SWAPFILE | opflags, iomap,
> +				srcmap);
> +}
> +
> +static const struct iomap_ops fuse_iomap_swapfile_ops = {
> +	.iomap_begin		= fuse_iomap_swapfile_begin,
> +};
> +
> +static int fuse_iomap_swap_activate(struct swap_info_struct *sis,
> +				    struct file *swap_file, sector_t *span)
> +{
> +	int ret;
> +
> +	/* obtain the block device from the header iomapping */
> +	sis->bdev = NULL;

Following up from a separate discussion on fsdevel about zoned storage
vs. swapfile activation, fuse_iomap_begin should not allow mappings to
zoned storage for swapon.  And maybe I should refactor the fuse
iomap_begin interface to provide the io context (pagecache io, directio,
fiemap, swapfile activation, pagecache writeback, etc) as a distinct
field rather than overlaying on the upper bits of the opflags.

--D

> +	ret = iomap_swapfile_activate(sis, swap_file, span,
> +				      &fuse_iomap_swapfile_ops);
> +	if (ret < 0)
> +		fuse_iomap_ioend(file_inode(swap_file), 0, 0, ret,
> +				 FUSE_IOMAP_IOEND_SWAPOFF, NULL,
> +				 FUSE_IOMAP_NULL_ADDR);
> +	return ret;
> +}
> +
> +static void fuse_iomap_swap_deactivate(struct file *file)
> +{
> +	fuse_iomap_ioend(file_inode(file), 0, 0, 0, FUSE_IOMAP_IOEND_SWAPOFF,
> +			 NULL, FUSE_IOMAP_NULL_ADDR);
> +}
> +#endif
> +
>  static const struct address_space_operations fuse_iomap_aops = {
>  	.read_folio		= fuse_iomap_read_folio,
>  	.readahead		= fuse_iomap_readahead,
> @@ -1811,6 +1859,10 @@ static const struct address_space_operations fuse_iomap_aops = {
>  	.migrate_folio		= filemap_migrate_folio,
>  	.is_partially_uptodate  = iomap_is_partially_uptodate,
>  	.error_remove_folio	= generic_error_remove_folio,
> +#ifdef CONFIG_SWAP
> +	.swap_activate		= fuse_iomap_swap_activate,
> +	.swap_deactivate	= fuse_iomap_swap_deactivate,
> +#endif
>  
>  	/* These aren't pagecache operations per se */
>  	.bmap			= fuse_bmap,
> 
>