On Thu, Jul 3, 2025 at 8:51 PM John Groves <j...@groves.net> wrote:
>
> On completion of GET_FMAP message/response, setup the full famfs
> metadata such that it's possible to handle read/write/mmap directly to
> dax. Note that the devdax_iomap plumbing is not in yet...
>
> Update MAINTAINERS for the new files.
>
> Signed-off-by: John Groves <j...@groves.net>
> ---
> MAINTAINERS | 9 +
> fs/fuse/Makefile | 2 +-
> fs/fuse/famfs.c | 360 ++++++++++++++++++++++++++++++++++++++
> fs/fuse/famfs_kfmap.h | 63 +++++++
> fs/fuse/file.c | 15 +-
> fs/fuse/fuse_i.h | 16 +-
> fs/fuse/inode.c | 2 +-
> include/uapi/linux/fuse.h | 56 ++++++
> 8 files changed, 518 insertions(+), 5 deletions(-)
> create mode 100644 fs/fuse/famfs.c
> create mode 100644 fs/fuse/famfs_kfmap.h
>
> diff --git a/MAINTAINERS b/MAINTAINERS
> index c0d5232a473b..02688f27a4d0 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -8808,6 +8808,15 @@ F: Documentation/networking/failover.rst
> F: include/net/failover.h
> F: net/core/failover.c
>
> +FAMFS
> +M: John Groves <jgro...@micron.com>
> +M: John Groves <j...@groves.net>
> +L: linux-...@vger.kernel.org
> +L: linux-fsde...@vger.kernel.org
> +S: Supported
> +F: fs/fuse/famfs.c
> +F: fs/fuse/famfs_kfmap.h
> +
I suggest to follow the pattern of MAINTAINERS sub entries
FILESYSTEMS [EXPORTFS]
FILESYSTEMS [IOMAP]
and call this sub entry
FUSE [FAMFS]
to order it following FUSE entry
Thanks,
Amir.
> FANOTIFY
> M: Jan Kara <j...@suse.cz>
> R: Amir Goldstein <amir7...@gmail.com>
> diff --git a/fs/fuse/Makefile b/fs/fuse/Makefile
> index 3f0f312a31c1..65a12975d734 100644
> --- a/fs/fuse/Makefile
> +++ b/fs/fuse/Makefile
> @@ -16,5 +16,5 @@ fuse-$(CONFIG_FUSE_DAX) += dax.o
> fuse-$(CONFIG_FUSE_PASSTHROUGH) += passthrough.o
> fuse-$(CONFIG_SYSCTL) += sysctl.o
> fuse-$(CONFIG_FUSE_IO_URING) += dev_uring.o
> -
> +fuse-$(CONFIG_FUSE_FAMFS_DAX) += famfs.o
> virtiofs-y := virtio_fs.o
> diff --git a/fs/fuse/famfs.c b/fs/fuse/famfs.c
> new file mode 100644
> index 000000000000..41c4d92f1451
> --- /dev/null
> +++ b/fs/fuse/famfs.c
> @@ -0,0 +1,360 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * famfs - dax file system for shared fabric-attached memory
> + *
> + * Copyright 2023-2025 Micron Technology, Inc.
> + *
> + * This file system, originally based on ramfs the dax support from xfs,
> + * is intended to allow multiple host systems to mount a common file system
> + * view of dax files that map to shared memory.
> + */
> +
> +#include <linux/fs.h>
> +#include <linux/mm.h>
> +#include <linux/dax.h>
> +#include <linux/iomap.h>
> +#include <linux/path.h>
> +#include <linux/namei.h>
> +#include <linux/string.h>
> +
> +#include "famfs_kfmap.h"
> +#include "fuse_i.h"
> +
> +
> +void
> +__famfs_meta_free(void *famfs_meta)
> +{
> + struct famfs_file_meta *fmap = famfs_meta;
> +
> + if (!fmap)
> + return;
> +
> + if (fmap) {
> + switch (fmap->fm_extent_type) {
> + case SIMPLE_DAX_EXTENT:
> + kfree(fmap->se);
> + break;
> + case INTERLEAVED_EXTENT:
> + if (fmap->ie)
> + kfree(fmap->ie->ie_strips);
> +
> + kfree(fmap->ie);
> + break;
> + default:
> + pr_err("%s: invalid fmap type\n", __func__);
> + break;
> + }
> + }
> + kfree(fmap);
> +}
> +
> +static int
> +famfs_check_ext_alignment(struct famfs_meta_simple_ext *se)
> +{
> + int errs = 0;
> +
> + if (se->dev_index != 0)
> + errs++;
> +
> + /* TODO: pass in alignment so we can support the other page sizes */
> + if (!IS_ALIGNED(se->ext_offset, PMD_SIZE))
> + errs++;
> +
> + if (!IS_ALIGNED(se->ext_len, PMD_SIZE))
> + errs++;
> +
> + return errs;
> +}
> +
> +/**
> + * famfs_fuse_meta_alloc() - Allocate famfs file metadata
> + * @metap: Pointer to an mcache_map_meta pointer
> + * @ext_count: The number of extents needed
> + *
> + * Returns: 0=success
> + * -errno=failure
> + */
> +static int
> +famfs_fuse_meta_alloc(
> + void *fmap_buf,
> + size_t fmap_buf_size,
> + struct famfs_file_meta **metap)
> +{
> + struct famfs_file_meta *meta = NULL;
> + struct fuse_famfs_fmap_header *fmh;
> + size_t extent_total = 0;
> + size_t next_offset = 0;
> + int errs = 0;
> + int i, j;
> + int rc;
> +
> + fmh = (struct fuse_famfs_fmap_header *)fmap_buf;
> +
> + /* Move past fmh in fmap_buf */
> + next_offset += sizeof(*fmh);
> + if (next_offset > fmap_buf_size) {
> + pr_err("%s:%d: fmap_buf underflow offset/size %ld/%ld\n",
> + __func__, __LINE__, next_offset, fmap_buf_size);
> + return -EINVAL;
> + }
> +
> + if (fmh->nextents < 1) {
> + pr_err("%s: nextents %d < 1\n", __func__, fmh->nextents);
> + return -EINVAL;
> + }
> +
> + if (fmh->nextents > FUSE_FAMFS_MAX_EXTENTS) {
> + pr_err("%s: nextents %d > max (%d) 1\n",
> + __func__, fmh->nextents, FUSE_FAMFS_MAX_EXTENTS);
> + return -E2BIG;
> + }
> +
> + meta = kzalloc(sizeof(*meta), GFP_KERNEL);
> + if (!meta)
> + return -ENOMEM;
> +
> + meta->error = false;
> + meta->file_type = fmh->file_type;
> + meta->file_size = fmh->file_size;
> + meta->fm_extent_type = fmh->ext_type;
> +
> + switch (fmh->ext_type) {
> + case FUSE_FAMFS_EXT_SIMPLE: {
> + struct fuse_famfs_simple_ext *se_in;
> +
> + se_in = (struct fuse_famfs_simple_ext *)(fmap_buf +
> next_offset);
> +
> + /* Move past simple extents */
> + next_offset += fmh->nextents * sizeof(*se_in);
> + if (next_offset > fmap_buf_size) {
> + pr_err("%s:%d: fmap_buf underflow offset/size
> %ld/%ld\n",
> + __func__, __LINE__, next_offset,
> fmap_buf_size);
> + rc = -EINVAL;
> + goto errout;
> + }
> +
> + meta->fm_nextents = fmh->nextents;
> +
> + meta->se = kcalloc(meta->fm_nextents, sizeof(*(meta->se)),
> + GFP_KERNEL);
> + if (!meta->se) {
> + rc = -ENOMEM;
> + goto errout;
> + }
> +
> + if ((meta->fm_nextents > FUSE_FAMFS_MAX_EXTENTS) ||
> + (meta->fm_nextents < 1)) {
> + rc = -EINVAL;
> + goto errout;
> + }
> +
> + for (i = 0; i < fmh->nextents; i++) {
> + meta->se[i].dev_index = se_in[i].se_devindex;
> + meta->se[i].ext_offset = se_in[i].se_offset;
> + meta->se[i].ext_len = se_in[i].se_len;
> +
> + /* Record bitmap of referenced daxdev indices */
> + meta->dev_bitmap |= (1 << meta->se[i].dev_index);
> +
> + errs += famfs_check_ext_alignment(&meta->se[i]);
> +
> + extent_total += meta->se[i].ext_len;
> + }
> + break;
> + }
> +
> + case FUSE_FAMFS_EXT_INTERLEAVE: {
> + s64 size_remainder = meta->file_size;
> + struct fuse_famfs_iext *ie_in;
> + int niext = fmh->nextents;
> +
> + meta->fm_niext = niext;
> +
> + /* Allocate interleaved extent */
> + meta->ie = kcalloc(niext, sizeof(*(meta->ie)), GFP_KERNEL);
> + if (!meta->ie) {
> + rc = -ENOMEM;
> + goto errout;
> + }
> +
> + /*
> + * Each interleaved extent has a simple extent list of strips.
> + * Outer loop is over separate interleaved extents
> + */
> + for (i = 0; i < niext; i++) {
> + u64 nstrips;
> + struct fuse_famfs_simple_ext *sie_in;
> +
> + /* ie_in = one interleaved extent in fmap_buf */
> + ie_in = (struct fuse_famfs_iext *)
> + (fmap_buf + next_offset);
> +
> + /* Move past one interleaved extent header in
> fmap_buf */
> + next_offset += sizeof(*ie_in);
> + if (next_offset > fmap_buf_size) {
> + pr_err("%s:%d: fmap_buf underflow offset/size
> %ld/%ld\n",
> + __func__, __LINE__, next_offset,
> + fmap_buf_size);
> + rc = -EINVAL;
> + goto errout;
> + }
> +
> + nstrips = ie_in->ie_nstrips;
> + meta->ie[i].fie_chunk_size = ie_in->ie_chunk_size;
> + meta->ie[i].fie_nstrips = ie_in->ie_nstrips;
> + meta->ie[i].fie_nbytes = ie_in->ie_nbytes;
> +
> + if (!meta->ie[i].fie_nbytes) {
> + pr_err("%s: zero-length interleave!\n",
> + __func__);
> + rc = -EINVAL;
> + goto errout;
> + }
> +
> + /* sie_in = the strip extents in fmap_buf */
> + sie_in = (struct fuse_famfs_simple_ext *)
> + (fmap_buf + next_offset);
> +
> + /* Move past strip extents in fmap_buf */
> + next_offset += nstrips * sizeof(*sie_in);
> + if (next_offset > fmap_buf_size) {
> + pr_err("%s:%d: fmap_buf underflow offset/size
> %ld/%ld\n",
> + __func__, __LINE__, next_offset,
> + fmap_buf_size);
> + rc = -EINVAL;
> + goto errout;
> + }
> +
> + if ((nstrips > FUSE_FAMFS_MAX_STRIPS) || (nstrips <
> 1)) {
> + pr_err("%s: invalid nstrips=%lld (max=%d)\n",
> + __func__, nstrips,
> + FUSE_FAMFS_MAX_STRIPS);
> + errs++;
> + }
> +
> + /* Allocate strip extent array */
> + meta->ie[i].ie_strips = kcalloc(ie_in->ie_nstrips,
> + sizeof(meta->ie[i].ie_strips[0]),
> + GFP_KERNEL);
> + if (!meta->ie[i].ie_strips) {
> + rc = -ENOMEM;
> + goto errout;
> + }
> +
> + /* Inner loop is over strips */
> + for (j = 0; j < nstrips; j++) {
> + struct famfs_meta_simple_ext *strips_out;
> + u64 devindex = sie_in[j].se_devindex;
> + u64 offset = sie_in[j].se_offset;
> + u64 len = sie_in[j].se_len;
> +
> + strips_out = meta->ie[i].ie_strips;
> + strips_out[j].dev_index = devindex;
> + strips_out[j].ext_offset = offset;
> + strips_out[j].ext_len = len;
> +
> + /* Record bitmap of referenced daxdev indices
> */
> + meta->dev_bitmap |= (1 << devindex);
> +
> + extent_total += len;
> + errs +=
> famfs_check_ext_alignment(&strips_out[j]);
> + size_remainder -= len;
> + }
> + }
> +
> + if (size_remainder > 0) {
> + /* Sum of interleaved extent sizes is less than file
> size! */
> + pr_err("%s: size_remainder %lld (0x%llx)\n",
> + __func__, size_remainder, size_remainder);
> + rc = -EINVAL;
> + goto errout;
> + }
> + break;
> + }
> +
> + default:
> + pr_err("%s: invalid ext_type %d\n", __func__, fmh->ext_type);
> + rc = -EINVAL;
> + goto errout;
> + }
> +
> + if (errs > 0) {
> + pr_err("%s: %d alignment errors found\n", __func__, errs);
> + rc = -EINVAL;
> + goto errout;
> + }
> +
> + /* More sanity checks */
> + if (extent_total < meta->file_size) {
> + pr_err("%s: file size %ld larger than map size %ld\n",
> + __func__, meta->file_size, extent_total);
> + rc = -EINVAL;
> + goto errout;
> + }
> +
> + *metap = meta;
> +
> + return 0;
> +errout:
> + __famfs_meta_free(meta);
> + return rc;
> +}
> +
> +/**
> + * famfs_file_init_dax() - init famfs dax file metadata
> + *
> + * @fm: fuse_mount
> + * @inode: the inode
> + * @fmap_buf: fmap response message
> + * @fmap_size: Size of the fmap message
> + *
> + * Initialize famfs metadata for a file, based on the contents of the
> GET_FMAP
> + * response
> + *
> + * Return: 0=success
> + * -errno=failure
> + */
> +int
> +famfs_file_init_dax(
> + struct fuse_mount *fm,
> + struct inode *inode,
> + void *fmap_buf,
> + size_t fmap_size)
> +{
> + struct fuse_inode *fi = get_fuse_inode(inode);
> + struct famfs_file_meta *meta = NULL;
> + int rc;
> +
> + if (fi->famfs_meta) {
> + pr_notice("%s: i_no=%ld fmap_size=%ld ALREADY INITIALIZED\n",
> + __func__,
> + inode->i_ino, fmap_size);
> + return -EEXIST;
> + }
> +
> + rc = famfs_fuse_meta_alloc(fmap_buf, fmap_size, &meta);
> + if (rc)
> + goto errout;
> +
> + /* Publish the famfs metadata on fi->famfs_meta */
> + inode_lock(inode);
> + if (fi->famfs_meta) {
> + rc = -EEXIST; /* file already has famfs metadata */
> + } else {
> + if (famfs_meta_set(fi, meta) != NULL) {
> + pr_err("%s: file already had metadata\n", __func__);
> + rc = -EALREADY;
> + goto errout;
> + }
> + i_size_write(inode, meta->file_size);
> + inode->i_flags |= S_DAX;
> + }
> + inode_unlock(inode);
> +
> + errout:
> + if (rc)
> + __famfs_meta_free(meta);
> +
> + return rc;
> +}
> +
> diff --git a/fs/fuse/famfs_kfmap.h b/fs/fuse/famfs_kfmap.h
> new file mode 100644
> index 000000000000..ce785d76719c
> --- /dev/null
> +++ b/fs/fuse/famfs_kfmap.h
> @@ -0,0 +1,63 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * famfs - dax file system for shared fabric-attached memory
> + *
> + * Copyright 2023-2025 Micron Technology, Inc.
> + */
> +#ifndef FAMFS_KFMAP_H
> +#define FAMFS_KFMAP_H
> +
> +/*
> + * These structures are the in-memory metadata format for famfs files.
> Metadata
> + * retrieved via the GET_FMAP response is converted to this format for use in
> + * resolving file mapping faults.
> + */
> +
> +enum famfs_file_type {
> + FAMFS_REG,
> + FAMFS_SUPERBLOCK,
> + FAMFS_LOG,
> +};
> +
> +/* We anticipate the possiblity of supporting additional types of extents */
> +enum famfs_extent_type {
> + SIMPLE_DAX_EXTENT,
> + INTERLEAVED_EXTENT,
> + INVALID_EXTENT_TYPE,
> +};
> +
> +struct famfs_meta_simple_ext {
> + u64 dev_index;
> + u64 ext_offset;
> + u64 ext_len;
> +};
> +
> +struct famfs_meta_interleaved_ext {
> + u64 fie_nstrips;
> + u64 fie_chunk_size;
> + u64 fie_nbytes;
> + struct famfs_meta_simple_ext *ie_strips;
> +};
> +
> +/*
> + * Each famfs dax file has this hanging from its fuse_inode->famfs_meta
> + */
> +struct famfs_file_meta {
> + bool error;
> + enum famfs_file_type file_type;
> + size_t file_size;
> + enum famfs_extent_type fm_extent_type;
> + u64 dev_bitmap; /* bitmap of referenced daxdevs by index */
> + union { /* This will make code a bit more readable */
> + struct {
> + size_t fm_nextents;
> + struct famfs_meta_simple_ext *se;
> + };
> + struct {
> + size_t fm_niext;
> + struct famfs_meta_interleaved_ext *ie;
> + };
> + };
> +};
> +
> +#endif /* FAMFS_KFMAP_H */
> diff --git a/fs/fuse/file.c b/fs/fuse/file.c
> index 8616fb0a6d61..5d205eadb48f 100644
> --- a/fs/fuse/file.c
> +++ b/fs/fuse/file.c
> @@ -237,6 +237,7 @@ static void fuse_truncate_update_attr(struct inode
> *inode, struct file *file)
> static int
> fuse_get_fmap(struct fuse_mount *fm, struct inode *inode, u64 nodeid)
> {
> + struct fuse_inode *fi = get_fuse_inode(inode);
> struct fuse_get_fmap_in inarg = { 0 };
> size_t fmap_bufsize = FMAP_BUFSIZE;
> ssize_t fmap_size;
> @@ -246,6 +247,10 @@ fuse_get_fmap(struct fuse_mount *fm, struct inode
> *inode, u64 nodeid)
>
> FUSE_ARGS(args);
>
> + /* Don't retrieve if we already have the famfs metadata */
> + if (fi->famfs_meta)
> + return 0;
> +
> fmap_buf = kcalloc(1, FMAP_BUFSIZE, GFP_KERNEL);
> if (!fmap_buf)
> return -EIO;
> @@ -285,6 +290,13 @@ fuse_get_fmap(struct fuse_mount *fm, struct inode
> *inode, u64 nodeid)
> */
> fmap_bufsize = *((uint32_t *)fmap_buf);
>
> + if (fmap_bufsize < fmap_msg_min_size()
> + || fmap_bufsize > FAMFS_FMAP_MAX) {
> + pr_err("%s: fmap_size=%ld out of range\n",
> + __func__, fmap_bufsize);
> + return -EIO;
> + }
> +
> --retries;
> kfree(fmap_buf);
> fmap_buf = kcalloc(1, fmap_bufsize, GFP_KERNEL);
> @@ -294,7 +306,8 @@ fuse_get_fmap(struct fuse_mount *fm, struct inode *inode,
> u64 nodeid)
> goto retry_once;
> }
>
> - /* Will call famfs_file_init_dax() when that gets added */
> + /* Convert fmap into in-memory format and hang from inode */
> + famfs_file_init_dax(fm, inode, fmap_buf, fmap_size);
>
> kfree(fmap_buf);
> return 0;
> diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
> index e01d6e5c6e93..fb6095655403 100644
> --- a/fs/fuse/fuse_i.h
> +++ b/fs/fuse/fuse_i.h
> @@ -1560,11 +1560,18 @@ extern void fuse_sysctl_unregister(void);
> #endif /* CONFIG_SYSCTL */
>
> /* famfs.c */
> +#if IS_ENABLED(CONFIG_FUSE_FAMFS_DAX)
> +int famfs_file_init_dax(struct fuse_mount *fm,
> + struct inode *inode, void *fmap_buf,
> + size_t fmap_size);
> +void __famfs_meta_free(void *map);
> +#endif
> +
> static inline struct fuse_backing *famfs_meta_set(struct fuse_inode *fi,
> void *meta)
> {
> #if IS_ENABLED(CONFIG_FUSE_FAMFS_DAX)
> - return xchg(&fi->famfs_meta, meta);
> + return cmpxchg(&fi->famfs_meta, NULL, meta);
> #else
> return NULL;
> #endif
> @@ -1572,7 +1579,12 @@ static inline struct fuse_backing
> *famfs_meta_set(struct fuse_inode *fi,
>
> static inline void famfs_meta_free(struct fuse_inode *fi)
> {
> - /* Stub wil be connected in a subsequent commit */
> +#if IS_ENABLED(CONFIG_FUSE_FAMFS_DAX)
> + if (fi->famfs_meta != NULL) {
> + __famfs_meta_free(fi->famfs_meta);
> + famfs_meta_set(fi, NULL);
> + }
> +#endif
> }
>
> static inline int fuse_file_famfs(struct fuse_inode *fi)
> diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
> index b071d16f7d04..1682755abf30 100644
> --- a/fs/fuse/inode.c
> +++ b/fs/fuse/inode.c
> @@ -118,7 +118,7 @@ static struct inode *fuse_alloc_inode(struct super_block
> *sb)
> fuse_inode_backing_set(fi, NULL);
>
> if (IS_ENABLED(CONFIG_FUSE_FAMFS_DAX))
> - famfs_meta_set(fi, NULL);
> + fi->famfs_meta = NULL; /* XXX new inodes currently not
> zeroed; why not? */
>
> return &fi->inode;
>
> diff --git a/include/uapi/linux/fuse.h b/include/uapi/linux/fuse.h
> index dff5aa62543e..ecaaa62910f0 100644
> --- a/include/uapi/linux/fuse.h
> +++ b/include/uapi/linux/fuse.h
> @@ -231,6 +231,13 @@
> * - enum fuse_uring_cmd
> * 7.43
> * - Add FUSE_DAX_FMAP capability - ability to handle in-kernel fsdax maps
> + * - Add the following structures for the GET_FMAP message reply
> components:
> + * - struct fuse_famfs_simple_ext
> + * - struct fuse_famfs_iext
> + * - struct fuse_famfs_fmap_header
> + * - Add the following enumerated types
> + * - enum fuse_famfs_file_type
> + * - enum famfs_ext_type
> */
>
> #ifndef _LINUX_FUSE_H
> @@ -1300,6 +1307,55 @@ struct fuse_uring_cmd_req {
>
> /* Famfs fmap message components */
>
> +#define FAMFS_FMAP_VERSION 1
> +
> #define FAMFS_FMAP_MAX 32768 /* Largest supported fmap message */
> +#define FUSE_FAMFS_MAX_EXTENTS 32
> +#define FUSE_FAMFS_MAX_STRIPS 32
> +
> +enum fuse_famfs_file_type {
> + FUSE_FAMFS_FILE_REG,
> + FUSE_FAMFS_FILE_SUPERBLOCK,
> + FUSE_FAMFS_FILE_LOG,
> +};
> +
> +enum famfs_ext_type {
> + FUSE_FAMFS_EXT_SIMPLE = 0,
> + FUSE_FAMFS_EXT_INTERLEAVE = 1,
> +};
> +
> +struct fuse_famfs_simple_ext {
> + uint32_t se_devindex;
> + uint32_t reserved;
> + uint64_t se_offset;
> + uint64_t se_len;
> +};
> +
> +struct fuse_famfs_iext { /* Interleaved extent */
> + uint32_t ie_nstrips;
> + uint32_t ie_chunk_size;
> + uint64_t ie_nbytes; /* Total bytes for this interleaved_ext;
> + * sum of strips may be more
> + */
> + uint64_t reserved;
> +};
> +
> +struct fuse_famfs_fmap_header {
> + uint8_t file_type; /* enum famfs_file_type */
> + uint8_t reserved;
> + uint16_t fmap_version;
> + uint32_t ext_type; /* enum famfs_log_ext_type */
> + uint32_t nextents;
> + uint32_t reserved0;
> + uint64_t file_size;
> + uint64_t reserved1;
> +};
> +
> +static inline int32_t fmap_msg_min_size(void)
> +{
> + /* Smallest fmap message is a header plus one simple extent */
> + return (sizeof(struct fuse_famfs_fmap_header)
> + + sizeof(struct fuse_famfs_simple_ext));
> +}
>
> #endif /* _LINUX_FUSE_H */
> --
> 2.49.0
>
