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

John Groves
2026-02-25T21:30:39Z

On 26/02/19 11:31AM, Dave Jiang wrote:
>
>
> 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

Done, thanks!

>
> > + 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?

Done, Thx

>
> > +
> > + 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);

Ah, I didn't know that one!

Done

>
> > +
> > + 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

Another new one to me!

Done.

Thanks Dave!

[snip]