Re: [PATCH V7 13/19] famfs_fuse: Create files with famfs fmaps

[Dave Jiang <dave.jiang@intel.com>]

On 1/18/26 3:33 PM, John Groves wrote:
> From: John Groves <john@groves.net>
> 
> 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...
> 
> * Add famfs_kfmap.h: in-memory structures for resolving famfs file maps
>   (fmaps) to dax.
> * famfs.c: allocate, initialize and free fmaps
> * inode.c: only allow famfs mode if the fuse server has CAP_SYS_RAWIO
> * Update MAINTAINERS for the new file.
> 
> Signed-off-by: John Groves <john@groves.net>
> ---
>  MAINTAINERS               |   1 +
>  fs/fuse/famfs.c           | 339 +++++++++++++++++++++++++++++++++++++-
>  fs/fuse/famfs_kfmap.h     |  67 ++++++++
>  fs/fuse/fuse_i.h          |   8 +-
>  fs/fuse/inode.c           |  19 ++-
>  include/uapi/linux/fuse.h |  56 +++++++
>  6 files changed, 480 insertions(+), 10 deletions(-)
>  create mode 100644 fs/fuse/famfs_kfmap.h
> 
> diff --git a/MAINTAINERS b/MAINTAINERS
> index e3d0aa5eb361..6f8a7c813c2f 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -10386,6 +10386,7 @@ L:	linux-cxl@vger.kernel.org
>  L:	linux-fsdevel@vger.kernel.org
>  S:	Supported
>  F:	fs/fuse/famfs.c
> +F:	fs/fuse/famfs_kfmap.h
>  
>  FUTEX SUBSYSTEM
>  M:	Thomas Gleixner <tglx@kernel.org>
> diff --git a/fs/fuse/famfs.c b/fs/fuse/famfs.c
> index 615819cc922d..a9728e11f1dd 100644
> --- a/fs/fuse/famfs.c
> +++ b/fs/fuse/famfs.c
> @@ -18,9 +18,339 @@
>  #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;
> +
> +	switch (fmap->fm_extent_type) {
> +	case SIMPLE_DAX_EXTENT:
> +		kfree(fmap->se);
> +		break;
> +	case INTERLEAVED_EXTENT:
> +		if (fmap->ie) {
> +			for (int i = 0; i < fmap->fm_niext; i++)
> +				kfree(fmap->ie[i].ie_strips);
> +		}
> +		kfree(fmap->ie);
> +		break;
> +	default:
> +		pr_err("%s: invalid fmap type\n", __func__);
> +		break;
> +	}
> +
> +	kfree(fmap);
> +}
> +DEFINE_FREE(__famfs_meta_free, void *, if (_T) __famfs_meta_free(_T))
> +
> +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
> + * @fmap_buf:  fmap buffer from fuse server
> + * @fmap_buf_size: size of fmap buffer
> + * @metap:         pointer where 'struct famfs_file_meta' is returned
> + *
> + * 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 __free(__famfs_meta_free) = NULL;

declare when it gets allocated

> +	struct fuse_famfs_fmap_header *fmh;
> +	size_t extent_total = 0;
> +	size_t next_offset = 0;
> +	int errs = 0;
> +	int i, j;
> +
> +	fmh = 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;
> +	}

Both checks for nextents can be -ERANGE?

> +
> +	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 = 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);
> +			return -EINVAL;
> +		}
> +
> +		meta->fm_nextents = fmh->nextents;
> +
> +		meta->se = kcalloc(meta->fm_nextents, sizeof(*(meta->se)),
> +				   GFP_KERNEL);
> +		if (!meta->se)
> +			return -ENOMEM;
> +
> +		if ((meta->fm_nextents > FUSE_FAMFS_MAX_EXTENTS) ||
> +		    (meta->fm_nextents < 1))
> +			return -EINVAL;
> +> +		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)
> +			return -ENOMEM;
> +
> +		/*
> +		 * 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 = 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);
> +				return -EINVAL;
> +			}
> +
> +			if (!IS_ALIGNED(ie_in->ie_chunk_size, PMD_SIZE)) {
> +				pr_err("%s: chunk_size %lld not PMD-aligned\n",
> +				       __func__, meta->ie[i].fie_chunk_size);
> +				return -EINVAL;
> +			}
> +
> +			if (ie_in->ie_nbytes == 0) {
> +				pr_err("%s: zero-length interleave!\n",
> +				       __func__);
> +				return -EINVAL;
> +			}
> +
> +			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;
> +
> +			/* sie_in = the strip extents in fmap_buf */
> +			sie_in = 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);
> +				return -EINVAL;
> +			}
> +
> +			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)
> +				return -ENOMEM;
> +
> +			/* 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);
> +			return -EINVAL;
> +		}
> +		break;
> +	}
> +
> +	default:
> +		pr_err("%s: invalid ext_type %d\n", __func__, fmh->ext_type);
> +		return -EINVAL;
> +	}
> +
> +	if (errs > 0) {
> +		pr_err("%s: %d alignment errors found\n", __func__, errs);
> +		return -EINVAL;
> +	}
> +
> +	/* 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);
> +		return -EINVAL;
> +	}
> +
> +	if (cmpxchg(metap, NULL, meta) != NULL) {
> +		pr_debug("%s: fmap race detected\n", __func__);
> +		return 0; /* fmap already installed */
> +	}
> +	meta = NULL; /* disarm __free() - the meta struct was consumed */

I think you can do:
retain_and_null_ptr(meta);

> +
> +	return 0;
> +}
> +
> +/**
> + * 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 0;
> +	}
> +
> +	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 (famfs_meta_set(fi, meta) == NULL) {
> +		i_size_write(inode, meta->file_size);
> +		inode->i_flags |= S_DAX;
> +	} else {
> +		pr_debug("%s: file already had metadata\n", __func__);
> +		__famfs_meta_free(meta);
> +		/* rc is 0 - the file is valid */
> +	}
> +
> +	inode_unlock(inode);
> +	return 0;
> +
> +errout:
> +	if (rc)
> +		__famfs_meta_free(meta);
> +
> +	return rc;
> +}
> +
>  #define FMAP_BUFSIZE PAGE_SIZE
>  
>  int
> @@ -64,11 +394,8 @@ fuse_get_fmap(struct fuse_mount *fm, struct inode *inode)
>  	}
>  	fmap_size = rc;
>  
> -	/* We retrieved the "fmap" (the file's map to memory), but
> -	 * we haven't used it yet. A call to famfs_file_init_dax() will be added
> -	 * here in a subsequent patch, when we add the ability to attach
> -	 * fmaps to files.
> -	 */
> +	/* Convert fmap into in-memory format and hang from inode */
> +	rc = famfs_file_init_dax(fm, inode, fmap_buf, fmap_size);
>  
> -	return 0;
> +	return rc;
>  }
> diff --git a/fs/fuse/famfs_kfmap.h b/fs/fuse/famfs_kfmap.h
> new file mode 100644
> index 000000000000..18ab22bcc5a1
> --- /dev/null
> +++ b/fs/fuse/famfs_kfmap.h
> @@ -0,0 +1,67 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * famfs - dax file system for shared fabric-attached memory
> + *
> + * Copyright 2023-2026 Micron Technology, Inc.
> + */
> +#ifndef FAMFS_KFMAP_H
> +#define FAMFS_KFMAP_H
> +
> +/*
> + * The structures below 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.
> + *
> + * The GET_FMAP response contains the same information, but in a more
> + * message-and-versioning-friendly format. Those structs can be found in the
> + * famfs section of include/uapi/linux/fuse.h (aka fuse_kernel.h in libfuse)
> + */
> +
> +enum famfs_file_type {
> +	FAMFS_REG,
> +	FAMFS_SUPERBLOCK,
> +	FAMFS_LOG,
> +};
> +
> +/* We anticipate the possibility 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 {
> +		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/fuse_i.h b/fs/fuse/fuse_i.h
> index b66b5ca0bc11..dbfec5b9c6e1 100644
> --- a/fs/fuse/fuse_i.h
> +++ b/fs/fuse/fuse_i.h
> @@ -1642,6 +1642,9 @@ extern void fuse_sysctl_unregister(void);
>  /* 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);
>  
>  /* Set fi->famfs_meta = NULL regardless of prior value */
> @@ -1659,7 +1662,10 @@ static inline struct fuse_backing *famfs_meta_set(struct fuse_inode *fi,
>  
>  static inline void famfs_meta_free(struct fuse_inode *fi)
>  {
> -	famfs_meta_set(fi, NULL);
> +	if (fi->famfs_meta != NULL) {
> +		__famfs_meta_free(fi->famfs_meta);
> +		famfs_meta_set(fi, NULL);
> +	}
>  }
>  
>  static inline int fuse_file_famfs(struct fuse_inode *fi)
> diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
> index f2d742d723dc..b9933d0fbb9f 100644
> --- a/fs/fuse/inode.c
> +++ b/fs/fuse/inode.c
> @@ -1464,8 +1464,21 @@ static void process_init_reply(struct fuse_mount *fm, struct fuse_args *args,
>  				timeout = arg->request_timeout;
>  
>  			if (IS_ENABLED(CONFIG_FUSE_FAMFS_DAX) &&
> -			    flags & FUSE_DAX_FMAP)
> -				fc->famfs_iomap = 1;
> +			    flags & FUSE_DAX_FMAP) {
> +				/* famfs_iomap is only allowed if the fuse
> +				 * server has CAP_SYS_RAWIO. This was checked
> +				 * in fuse_send_init, and FUSE_DAX_IOMAP was
> +				 * set in in_flags if so. Only allow enablement
> +				 * if we find it there. This function is
> +				 * normally not running in fuse server context,
> +				 * so we can't do the capability check here...
> +				 */
> +				u64 in_flags = ((u64)ia->in.flags2 << 32)

FIELD_PREP()?

DJ

> +						| ia->in.flags;
> +
> +				if (in_flags & FUSE_DAX_FMAP)
> +					fc->famfs_iomap = 1;
> +			}
>  		} else {
>  			ra_pages = fc->max_read / PAGE_SIZE;
>  			fc->no_lock = 1;
> @@ -1527,7 +1540,7 @@ static struct fuse_init_args *fuse_new_init(struct fuse_mount *fm)
>  		flags |= FUSE_SUBMOUNTS;
>  	if (IS_ENABLED(CONFIG_FUSE_PASSTHROUGH))
>  		flags |= FUSE_PASSTHROUGH;
> -	if (IS_ENABLED(CONFIG_FUSE_FAMFS_DAX))
> +	if (IS_ENABLED(CONFIG_FUSE_FAMFS_DAX) && capable(CAP_SYS_RAWIO))
>  		flags |= FUSE_DAX_FMAP;
>  
>  	/*
> diff --git a/include/uapi/linux/fuse.h b/include/uapi/linux/fuse.h
> index 9eff9083d3b5..cf678bebbfe0 100644
> --- a/include/uapi/linux/fuse.h
> +++ b/include/uapi/linux/fuse.h
> @@ -243,6 +243,13 @@
>   *
>   *  7.46
>   *  - 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
> @@ -1318,6 +1325,55 @@ 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 */