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Message-ID: <20260114061028.GF15551@frogsfrogsfrogs>
Date: Tue, 13 Jan 2026 22:10:28 -0800
From: "Darrick J. Wong" <djwong@...nel.org>
To: André Almeida <andrealmeid@...lia.com>
Cc: Christoph Hellwig <hch@....de>, Chuck Lever <chuck.lever@...cle.com>,
Jeff Layton <jlayton@...nel.org>, NeilBrown <neil@...wn.name>,
Olga Kornievskaia <okorniev@...hat.com>,
Dai Ngo <Dai.Ngo@...cle.com>, Tom Talpey <tom@...pey.com>,
Carlos Maiolino <cem@...nel.org>,
Amir Goldstein <amir73il@...il.com>, Chris Mason <clm@...com>,
David Sterba <dsterba@...e.com>, Miklos Szeredi <miklos@...redi.hu>,
Christian Brauner <brauner@...nel.org>,
Alexander Viro <viro@...iv.linux.org.uk>, Jan Kara <jack@...e.cz>,
linux-nfs@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-xfs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
linux-btrfs@...r.kernel.org, linux-unionfs@...r.kernel.org,
kernel-dev@...lia.com
Subject: Re: [PATCH 1/3] exportfs: Rename get_uuid() to get_disk_uuid()
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@...lia.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
>
>
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