Re: [PATCH 1/3] exportfs: Rename get_uuid() to get_disk_uuid()

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

On Wed, Jan 14, 2026 at 01:31:41AM -0300, André Almeida wrote:
> To make clear which UUID is being returned, rename get_uuid() to
> get_disk_uuid(). Expand the function documentation to note that this
> function can be also used for filesystem that supports cloned devices
> that might have different UUIDs for userspace tools, while having the
> same UUID for internal usage.

I'm not sure what a "disk uuid" is -- XFS can store two of them in the
ondisk superblock: the admin-modifiable one that blkid reports, and the
secret one that's stamped in all the metadata and cannot change.

IIRC XFS only shares the user-visible UUID, but they're both from the
disk.   Also I'm not sure what a non-disk filesystem is supposed to
provide here?

--D

> Signed-off-by: André Almeida <andrealmeid@igalia.com>
> ---
>  fs/nfsd/blocklayout.c    | 2 +-
>  fs/nfsd/nfs4layouts.c    | 2 +-
>  fs/xfs/xfs_export.c      | 2 +-
>  fs/xfs/xfs_pnfs.c        | 2 +-
>  fs/xfs/xfs_pnfs.h        | 2 +-
>  include/linux/exportfs.h | 8 +++++---
>  6 files changed, 10 insertions(+), 8 deletions(-)
> 
> diff --git a/fs/nfsd/blocklayout.c b/fs/nfsd/blocklayout.c
> index afa16d7a8013..713a1f69f8fe 100644
> --- a/fs/nfsd/blocklayout.c
> +++ b/fs/nfsd/blocklayout.c
> @@ -218,7 +218,7 @@ nfsd4_block_get_device_info_simple(struct super_block *sb,
>  
>  	b->type = PNFS_BLOCK_VOLUME_SIMPLE;
>  	b->simple.sig_len = PNFS_BLOCK_UUID_LEN;
> -	return sb->s_export_op->get_uuid(sb, b->simple.sig, &b->simple.sig_len,
> +	return sb->s_export_op->get_disk_uuid(sb, b->simple.sig, &b->simple.sig_len,
>  			&b->simple.offset);
>  }
>  
> diff --git a/fs/nfsd/nfs4layouts.c b/fs/nfsd/nfs4layouts.c
> index ad7af8cfcf1f..50bb29b2017c 100644
> --- a/fs/nfsd/nfs4layouts.c
> +++ b/fs/nfsd/nfs4layouts.c
> @@ -136,7 +136,7 @@ void nfsd4_setup_layout_type(struct svc_export *exp)
>  	exp->ex_layout_types |= 1 << LAYOUT_FLEX_FILES;
>  #endif
>  #ifdef CONFIG_NFSD_BLOCKLAYOUT
> -	if (sb->s_export_op->get_uuid &&
> +	if (sb->s_export_op->get_disk_uuid &&
>  	    sb->s_export_op->map_blocks &&
>  	    sb->s_export_op->commit_blocks)
>  		exp->ex_layout_types |= 1 << LAYOUT_BLOCK_VOLUME;
> diff --git a/fs/xfs/xfs_export.c b/fs/xfs/xfs_export.c
> index 201489d3de08..d09570ba7445 100644
> --- a/fs/xfs/xfs_export.c
> +++ b/fs/xfs/xfs_export.c
> @@ -244,7 +244,7 @@ const struct export_operations xfs_export_operations = {
>  	.get_parent		= xfs_fs_get_parent,
>  	.commit_metadata	= xfs_fs_nfs_commit_metadata,
>  #ifdef CONFIG_EXPORTFS_BLOCK_OPS
> -	.get_uuid		= xfs_fs_get_uuid,
> +	.get_disk_uuid		= xfs_fs_get_disk_uuid,
>  	.map_blocks		= xfs_fs_map_blocks,
>  	.commit_blocks		= xfs_fs_commit_blocks,
>  #endif
> diff --git a/fs/xfs/xfs_pnfs.c b/fs/xfs/xfs_pnfs.c
> index afe7497012d4..6ef7b29c4060 100644
> --- a/fs/xfs/xfs_pnfs.c
> +++ b/fs/xfs/xfs_pnfs.c
> @@ -50,7 +50,7 @@ xfs_break_leased_layouts(
>   * the exported device.
>   */
>  int
> -xfs_fs_get_uuid(
> +xfs_fs_get_disk_uuid(
>  	struct super_block	*sb,
>  	u8			*buf,
>  	u32			*len,
> diff --git a/fs/xfs/xfs_pnfs.h b/fs/xfs/xfs_pnfs.h
> index 940c6c2ad88c..df82a6ba1a11 100644
> --- a/fs/xfs/xfs_pnfs.h
> +++ b/fs/xfs/xfs_pnfs.h
> @@ -3,7 +3,7 @@
>  #define _XFS_PNFS_H 1
>  
>  #ifdef CONFIG_EXPORTFS_BLOCK_OPS
> -int xfs_fs_get_uuid(struct super_block *sb, u8 *buf, u32 *len, u64 *offset);
> +int xfs_fs_get_disk_uuid(struct super_block *sb, u8 *buf, u32 *len, u64 *offset);
>  int xfs_fs_map_blocks(struct inode *inode, loff_t offset, u64 length,
>  		struct iomap *iomap, bool write, u32 *device_generation);
>  int xfs_fs_commit_blocks(struct inode *inode, struct iomap *maps, int nr_maps,
> diff --git a/include/linux/exportfs.h b/include/linux/exportfs.h
> index 262e24d83313..dc7029949a62 100644
> --- a/include/linux/exportfs.h
> +++ b/include/linux/exportfs.h
> @@ -252,8 +252,10 @@ struct handle_to_path_ctx {
>   * @commit_metadata:
>   *    @commit_metadata should commit metadata changes to stable storage.
>   *
> - * @get_uuid:
> - *    Get a filesystem unique signature exposed to clients.
> + * @get_disk_uuid:
> + *    Get a filesystem unique signature exposed to clients. It's also useful for
> + *    filesystems that support mounting cloned disks and export different UUIDs
> + *    for userspace, while being internally the same.
>   *
>   * @map_blocks:
>   *    Map and, if necessary, allocate blocks for a layout.
> @@ -282,7 +284,7 @@ struct export_operations {
>  	struct dentry * (*get_parent)(struct dentry *child);
>  	int (*commit_metadata)(struct inode *inode);
>  
> -	int (*get_uuid)(struct super_block *sb, u8 *buf, u32 *len, u64 *offset);
> +	int (*get_disk_uuid)(struct super_block *sb, u8 *buf, u32 *len, u64 *offset);
>  	int (*map_blocks)(struct inode *inode, loff_t offset,
>  			  u64 len, struct iomap *iomap,
>  			  bool write, u32 *device_generation);
> 
> -- 
> 2.52.0
> 
>