Re: [PATCH 4/4] exportfs,nfsd: rework checking for layout-based block device access support

Jeff Layton
2026-03-31T17:52:13Z

On Tue, 2026-03-31 at 17:33 +0200, Christoph Hellwig wrote:
> Currently NFSD hard codes checking support for block-style layouts.
> Lift the checks into a file system-helper and provide a exportfs-level
> helper to implement the typical checks.
>
> This prepares for supporting block layout export of multiple devices
> per file system.
>
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
> fs/nfsd/export.c | 3 +-
> fs/nfsd/nfs4layouts.c | 26 +++++------------
> fs/xfs/xfs_pnfs.c | 13 +++++++++
> include/linux/exportfs_block.h | 52 +++++++++++++++++++++++++++++++++-
> 4 files changed, 73 insertions(+), 21 deletions(-)
>
> diff --git a/fs/nfsd/export.c b/fs/nfsd/export.c
> index 8e8a76a44ff0..e20298f9212f 100644
> --- a/fs/nfsd/export.c
> +++ b/fs/nfsd/export.c
> @@ -735,7 +735,8 @@ static int svc_export_parse(struct cache_detail *cd, char *mesg, int mlen)
> goto out4;
> err = 0;
>
> - nfsd4_setup_layout_type(&exp);
> + if (exp.ex_flags & NFSEXP_PNFS)
> + nfsd4_setup_layout_type(&exp);
> }
>
> expp = svc_export_lookup(&exp);
> diff --git a/fs/nfsd/nfs4layouts.c b/fs/nfsd/nfs4layouts.c
> index c53eb67969eb..7b849b637b5e 100644
> --- a/fs/nfsd/nfs4layouts.c
> +++ b/fs/nfsd/nfs4layouts.c
> @@ -2,7 +2,6 @@
> /*
> * Copyright (c) 2014 Christoph Hellwig.
> */
> -#include <linux/blkdev.h>
> #include <linux/exportfs_block.h>
> #include <linux/kmod.h>
> #include <linux/file.h>
> @@ -126,28 +125,17 @@ nfsd4_set_deviceid(struct nfsd4_deviceid *id, const struct svc_fh *fhp,
>
> void nfsd4_setup_layout_type(struct svc_export *exp)
> {
> -#if defined(CONFIG_NFSD_BLOCKLAYOUT) || defined(CONFIG_NFSD_SCSILAYOUT)
> struct super_block *sb = exp->ex_path.mnt->mnt_sb;
> - struct exportfs_block_ops *bops = sb->s_export_op->block_ops;
> -#endif
> -
> - if (!(exp->ex_flags & NFSEXP_PNFS))
> - return;
> + expfs_block_layouts_t block_supported = exporfs_layouts_supported(sb);
>
> -#ifdef CONFIG_NFSD_FLEXFILELAYOUT
> - exp->ex_layout_types |= 1 << LAYOUT_FLEX_FILES;
> -#endif
> -#ifdef CONFIG_NFSD_BLOCKLAYOUT
> - if (bops && bops->get_uuid && bops->map_blocks && bops->commit_blocks)
> + if (IS_ENABLED(CONFIG_NFSD_FLEXFILELAYOUT))
> + exp->ex_layout_types |= 1 << LAYOUT_FLEX_FILES;
> + if (IS_ENABLED(CONFIG_NFSD_BLOCKLAYOUT) &&
> + (block_supported & EXPFS_BLOCK_IN_BAND_ID))
> exp->ex_layout_types |= 1 << LAYOUT_BLOCK_VOLUME;
> -#endif
> -#ifdef CONFIG_NFSD_SCSILAYOUT
> - if (bops && bops->map_blocks && bops->commit_blocks &&
> - sb->s_bdev &&
> - sb->s_bdev->bd_disk->fops->pr_ops &&
> - sb->s_bdev->bd_disk->fops->get_unique_id)
> + if (IS_ENABLED(CONFIG_NFSD_SCSILAYOUT) &&
> + (block_supported & EXPFS_BLOCK_OUT_OF_BAND_ID))
> exp->ex_layout_types |= 1 << LAYOUT_SCSI;
> -#endif
> }
>
> void nfsd4_close_layout(struct nfs4_layout_stateid *ls)
> diff --git a/fs/xfs/xfs_pnfs.c b/fs/xfs/xfs_pnfs.c
> index fee782a3edbe..acefa0b99f53 100644
> --- a/fs/xfs/xfs_pnfs.c
> +++ b/fs/xfs/xfs_pnfs.c
> @@ -13,6 +13,7 @@
> #include "xfs_bmap.h"
> #include "xfs_iomap.h"
> #include "xfs_pnfs.h"
> +#include <linux/exportfs_block.h>
>
> /*
> * Ensure that we do not have any outstanding pNFS layouts that can be used by
> @@ -45,6 +46,17 @@ xfs_break_leased_layouts(
> return error;
> }
>
> +static expfs_block_layouts_t
> +xfs_fs_layouts_supported(
> + struct super_block *sb)
> +{
> + expfs_block_layouts_t supported = EXPFS_BLOCK_IN_BAND_ID;
> +
> + if (exportfs_bdev_supports_out_of_band_id(sb->s_bdev))
> + supported |= EXPFS_BLOCK_OUT_OF_BAND_ID;
> + return supported;
> +}
> +
> /*
> * Get a unique ID including its location so that the client can identify
> * the exported device.
> @@ -335,6 +347,7 @@ xfs_fs_commit_blocks(
> }
>
> struct exportfs_block_ops xfs_export_block_ops = {
> + .layouts_supported = xfs_fs_layouts_supported,
> .get_uuid = xfs_fs_get_uuid,
> .map_blocks = xfs_fs_map_blocks,
> .commit_blocks = xfs_fs_commit_blocks,
> diff --git a/include/linux/exportfs_block.h b/include/linux/exportfs_block.h
> index d1dec4689b14..8d5b0b0c5a82 100644
> --- a/include/linux/exportfs_block.h
> +++ b/include/linux/exportfs_block.h
> @@ -7,13 +7,35 @@
> #ifndef LINUX_EXPORTFS_BLOCK_H
> #define LINUX_EXPORTFS_BLOCK_H 1
>
> -#include <linux/types.h>
> +#include <linux/blkdev.h>
> +#include <linux/exportfs.h>
> +#include <linux/fs.h>
>
> struct inode;
> struct iomap;
> struct super_block;
>
> +/*
> + * There are the two types of block-style layout support:
> + * - In-band implies a device identified by a unique cookie inside the actual
> + * device address space checked by the ->get_uuid method as used by the pNFS
> + * block layout. This is a bit dangerous and deprecated.
> + * - Out of band implies identification by out of band unique identifiers
> + * specified by the storage protocol, which is much safer and used by the
> + * pNFS SCSI/NVMe layouts.
> + */
> +typedef unsigned int __bitwise expfs_block_layouts_t;
> +#define EXPFS_BLOCK_FLAG(__bit) \
> + ((__force expfs_block_layouts_t)(1u << __bit))
> +#define EXPFS_BLOCK_IN_BAND_ID EXPFS_BLOCK_FLAG(0)
> +#define EXPFS_BLOCK_OUT_OF_BAND_ID EXPFS_BLOCK_FLAG(1)
> +
> struct exportfs_block_ops {
> + /*
> + * Returns the EXPFS_BLOCK_* bitmap of supported layout types.
> + */
> + expfs_block_layouts_t (*layouts_supported)(struct super_block *sb);
> +
> /*
> * Get the in-band device unique signature exposed to clients.
> */
> @@ -35,4 +57,32 @@ struct exportfs_block_ops {
> int nr_iomaps, loff_t new_size);
> };
>
> +static inline bool
> +exportfs_bdev_supports_out_of_band_id(struct block_device *bdev)
> +{
> + return bdev->bd_disk->fops->pr_ops &&
> + bdev->bd_disk->fops->get_unique_id;
> +}
> +
> +#ifdef CONFIG_EXPORTFS_BLOCK_OPS
> +static inline expfs_block_layouts_t
> +exporfs_layouts_supported(struct super_block *sb)
> +{
> + struct exportfs_block_ops *bops = sb->s_export_op->block_ops;
> +
> + if (!bops ||
> + !bops->layouts_supported ||
> + WARN_ON_ONCE(!bops->map_blocks) ||
> + WARN_ON_ONCE(!bops->commit_blocks))
> + return 0;
> + return bops->layouts_supported(sb);
> +}
> +#else
> +static inline expfs_block_layouts_t
> +exporfs_layouts_supported(struct super_block *sb)
> +{
> + return 0;
> +}
> +#endif /* CONFIG_EXPORTFS_BLOCK_OPS */
> +
> #endif /* LINUX_EXPORTFS_BLOCK_H */

Much cleaner.