exportfs,nfsd: rework checking for layout-based block device access support

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>
Link: https://patch.msgid.link/20260423181854.743150-5-cel@kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>

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);

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)

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,

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 */