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

Chuck Lever
2026-04-23T18:15:12Z

From: Christoph Hellwig <hch@lst.de>

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>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
---
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 15972919e1e9..2584279a47ba 100644
--- a/fs/nfsd/export.c
+++ b/fs/nfsd/export.c
@@ -1435,7 +1435,8 @@ 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 cf5b7eb417c5..c3543d456702 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>
@@ -128,28 +127,17 @@ 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;
- const struct exportfs_block_ops *bops = sb->s_export_op->block_ops;
-#endif
+ expfs_block_layouts_t block_supported = exportfs_layouts_supported(sb);

- if (!(exp->ex_flags & NFSEXP_PNFS))
- return;
-
-#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 7d689bb2efd9..266a07601e8d 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(
}

const 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..de519b7b599b 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
+exportfs_layouts_supported(struct super_block *sb)
+{
+ const 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
+exportfs_layouts_supported(struct super_block *sb)
+{
+ return 0;
+}
+#endif /* CONFIG_EXPORTFS_BLOCK_OPS */
+
#endif /* LINUX_EXPORTFS_BLOCK_H */
--
2.53.0