On Mon, Aug 03, 2026 at 02:29:26AM +0000, John Groves wrote:
> From: John Groves <[email protected]>
>
> Add the famfs file ioctl handler (FAMFSIOC_NOP, FAMFSIOC_MAP_CREATE) and
> the KABI-44 self-describing fmap message: the wire ABI in famfs_ioctl.h
> (famfs_ioc_fmap_header plus the simple and interleaved extent structs), the
> in-core famfs_file_meta, and famfs_file_init_dax(), which copies the
> message in, parses both the simple-extent and interleaved (striped) wire
> forms into inode->i_private, and sets S_DAX.
>
> Resolving those mappings to dax-device offsets (iomap_begin) is added in
> the following commit; the read/write/fault paths keep their NULL iomap_ops
> stub until then.
>
> Also add famfs ioctls to ioctl-number.rst
>
> Signed-off-by: John Groves <[email protected]>
> ---
> .../userspace-api/ioctl/ioctl-number.rst | 1 +
> fs/famfs/famfs_file.c | 326 +++++++++++++++++-
> fs/famfs/famfs_inode.c | 1 +
> fs/famfs/famfs_internal.h | 46 +++
> include/uapi/linux/famfs_ioctl.h | 91 +++++
> 5 files changed, 462 insertions(+), 3 deletions(-)
> create mode 100644 include/uapi/linux/famfs_ioctl.h
>
> diff --git a/Documentation/userspace-api/ioctl/ioctl-number.rst
> b/Documentation/userspace-api/ioctl/ioctl-number.rst
> index 3f0ef1e27eb0..5e244dec1b98 100644
> --- a/Documentation/userspace-api/ioctl/ioctl-number.rst
> +++ b/Documentation/userspace-api/ioctl/ioctl-number.rst
> @@ -299,6 +299,7 @@ Code Seq# Include File
> Comments
> 'u' 00-2F linux/ublk_cmd.h
> conflict!
> 'u' 20-3F linux/uvcvideo.h USB
> video class host driver
> 'u' 40-4f linux/udmabuf.h
> userspace dma-buf misc device
> +'u' 50-5F linux/famfs_ioctl.h famfs
> shared memory file system
> 'v' 00-1F linux/ext2_fs.h
> conflict!
> 'v' 00-1F linux/fs.h
> conflict!
> 'v' 00-0F linux/sonypi.h
> conflict!
> diff --git a/fs/famfs/famfs_file.c b/fs/famfs/famfs_file.c
> index 678f2035fd5f..d710c8a0c923 100644
> --- a/fs/famfs/famfs_file.c
> +++ b/fs/famfs/famfs_file.c
> @@ -13,9 +13,313 @@
> #include <linux/mm.h>
> #include <linux/dax.h>
> #include <linux/iomap.h>
> +#include <linux/capability.h>
>
> +#include <linux/famfs_ioctl.h>
> #include "famfs_internal.h"
>
> +/* Expose famfs kernel abi version as a read-only module parameter */
> +static int famfs_kabi_version = FAMFS_KABI_VERSION;
> +module_param(famfs_kabi_version, int, 0444);
> +MODULE_PARM_DESC(famfs_kabi_version, "famfs kernel abi version");
Maybe make the "NOP" ioctl a geometry ioctl that tells you the abi
version and (I guess) the page and pmd size? :D
> +void
> +famfs_meta_free(struct famfs_file_meta *map)
> +{
> + if (map) {
> + switch (map->fm_extent_type) {
> + case FAMFS_IOC_EXT_SIMPLE:
> + kfree(map->se);
> + break;
> + case FAMFS_IOC_EXT_INTERLEAVE:
> + if (map->ie) {
> + u32 i;
> +
> + for (i = 0; i < map->fm_niext; i++)
> + kfree(map->ie[i].ie_strips);
> + }
> + kfree(map->ie);
> + break;
> + default:
> + break;
> + }
> + }
> + kfree(map);
> +}
> +
> +/**
> + * famfs_file_init_dax() - FAMFSIOC_MAP_CREATE ioctl handler
> + * @file: the un-initialized file
> + * @arg: user pointer to a self-describing fmap message
> + *
> + * The map-create ioctl carries the fmap as a self-describing message: a
> + * struct famfs_ioc_fmap_header followed by an extent list. The message is
> + * copied in, parsed into a famfs_file_meta, and published on
> inode->i_private.
> + * Both the simple-extent and the interleaved (striped) wire forms are
> handled.
> + * The wire layout byte-matches the fmap carried in a fuse famfs GET_FMAP
> reply.
> + */
This kerneldoc is for the next function?
> +static int
> +famfs_check_ext_alignment(struct famfs_meta_simple_ext *se)
> +{
> + int errs = 0;
> +
> + if (!IS_ALIGNED(se->ext_offset, PMD_SIZE))
> + errs++;
> + if (!IS_ALIGNED(se->ext_len, PMD_SIZE))
> + errs++;
Does this need to check the dax dev index is valid? Or is it ok to just
fail an IO if that index is garbage?
> +
> + return errs;
> +}
> +
> +static int
> +famfs_file_init_dax(struct file *file, void __user *arg)
> +{
> + struct famfs_ioc_fmap_header fmh;
> + struct famfs_file_meta *meta = NULL;
> + struct famfs_fs_info *fsi;
> + struct super_block *sb;
> + struct inode *inode;
> + void *fmap_buf = NULL;
> + size_t extent_total = 0;
> + size_t next_offset;
> + int errs = 0;
> + int rc;
> + u32 i, j;
> +
> + inode = file_inode(file);
> + if (!inode)
> + return -EBADF;
> + if (inode->i_private)
> + return -EEXIST;
> +
> + sb = inode->i_sb;
> + fsi = sb->s_fs_info;
> + if (fsi->deverror)
> + return -ENODEV;
> + if (!famfs_opt_enabled(fsi, FAMFS_OPT_MAP_CREATE))
> + return -EPERM;
> +
> + if (copy_from_user(&fmh, arg, sizeof(fmh)))
> + return -EFAULT;
> +
> + if (fmh.fmap_version != FAMFS_FMAP_VERSION)
> + return -EINVAL;
> + if (fmh.fmap_size < sizeof(fmh))
> + return -EINVAL;
> + if (fmh.fmap_size > FAMFS_FMAP_MSG_MAX)
> + return -EFBIG;
> + if (fmh.nextents < 1)
> + return -EINVAL;
> +
> + fmap_buf = kvmalloc(fmh.fmap_size, GFP_KERNEL);
> + if (!fmap_buf)
> + return -ENOMEM;
> +
> + if (copy_from_user(fmap_buf, arg, fmh.fmap_size)) {
> + rc = -EFAULT;
> + goto out;
> + }
> + next_offset = sizeof(fmh); /* start of the extent list */
> +
> + meta = kzalloc_obj(*meta, GFP_KERNEL);
> + if (!meta) {
> + rc = -ENOMEM;
> + goto out;
> + }
> +
> + 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 FAMFS_IOC_EXT_SIMPLE: {
> + struct famfs_ioc_simple_ext *se_in = fmap_buf + next_offset;
> +
> + next_offset += (size_t)fmh.nextents * sizeof(*se_in);
> + if (next_offset > fmh.fmap_size) {
> + rc = -EINVAL;
> + goto out;
> + }
> +
> + meta->fm_nextents = fmh.nextents;
> + meta->se = kcalloc(meta->fm_nextents, sizeof(*meta->se),
> + GFP_KERNEL);
> + if (!meta->se) {
> + rc = -ENOMEM;
> + goto out;
> + }
> +
> + 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;
> +
> + if (meta->se[i].dev_index >= FAMFS_MAX_DAXDEVS) {
> + rc = -EINVAL;
> + goto out;
> + }
> + meta->dev_bitmap |= BIT_ULL(meta->se[i].dev_index);
> + errs += famfs_check_ext_alignment(&meta->se[i]);
> + extent_total += meta->se[i].ext_len;
> + }
> + break;
> + }
> +
> + case FAMFS_IOC_EXT_INTERLEAVE: {
> + s64 size_remainder = meta->file_size;
> + u32 niext = fmh.nextents;
> +
> + meta->fm_niext = niext;
> + meta->ie = kcalloc(niext, sizeof(*meta->ie), GFP_KERNEL);
> + if (!meta->ie) {
> + rc = -ENOMEM;
> + goto out;
> + }
> +
> + /* Outer loop is over the separate interleaved extents */
> + for (i = 0; i < niext; i++) {
> + struct famfs_ioc_iext *ie_in = fmap_buf + next_offset;
> + struct famfs_ioc_simple_ext *sie_in;
> + u64 nstrips;
> +
> + next_offset += sizeof(*ie_in);
> + if (next_offset > fmh.fmap_size) {
> + rc = -EINVAL;
> + goto out;
> + }
> +
> + if (ie_in->ie_chunk_size == 0 ||
> + !IS_ALIGNED(ie_in->ie_chunk_size, PMD_SIZE)) {
> + rc = -EINVAL;
> + goto out;
> + }
> + if (ie_in->ie_nbytes == 0) {
> + rc = -EINVAL;
> + goto out;
> + }
> +
> + nstrips = ie_in->ie_nstrips;
> + if (nstrips < 1) {
> + rc = -EINVAL;
> + goto out;
> + }
> +
> + 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;
> +
> + /* The strip extents follow the interleaved-ext header
> */
> + sie_in = fmap_buf + next_offset;
> + next_offset += nstrips * sizeof(*sie_in);
> + if (next_offset > fmh.fmap_size) {
> + rc = -EINVAL;
> + goto out;
> + }
> +
> + meta->ie[i].ie_strips =
> + kcalloc(nstrips,
> sizeof(meta->ie[i].ie_strips[0]),
> + GFP_KERNEL);
> + if (!meta->ie[i].ie_strips) {
> + rc = -ENOMEM;
> + goto out;
> + }
> +
> + /* Inner loop is over the strips */
> + for (j = 0; j < nstrips; j++) {
> + struct famfs_meta_simple_ext *so =
> + &meta->ie[i].ie_strips[j];
> +
> + so->dev_index = sie_in[j].se_devindex;
> + so->ext_offset = sie_in[j].se_offset;
> + so->ext_len = sie_in[j].se_len;
> +
> + if (so->dev_index >= FAMFS_MAX_DAXDEVS) {
> + rc = -EINVAL;
> + goto out;
> + }
> + meta->dev_bitmap |= BIT_ULL(so->dev_index);
> + errs += famfs_check_ext_alignment(so);
> + extent_total += so->ext_len;
> + size_remainder -= so->ext_len;
This is a lot of indenting, maybe each case should be a separate helper
function?
--D
> + }
> + }
> +
> + if (size_remainder > 0) {
> + /* Strips do not cover the whole file */
> + rc = -EINVAL;
> + goto out;
> + }
> + break;
> + }
> +
> + default:
> + rc = -EINVAL;
> + goto out;
> + }
> +
> + if (errs > 0) {
> + rc = -EINVAL;
> + goto out;
> + }
> + if (extent_total < meta->file_size) {
> + rc = -EINVAL;
> + goto out;
> + }
> +
> + /* Publish the famfs metadata on inode->i_private */
> + inode_lock(inode);
> + if (inode->i_private) {
> + rc = -EEXIST; /* file already has famfs metadata */
> + } else {
> + inode->i_private = meta;
> + i_size_write(inode, meta->file_size);
> + inode->i_flags |= S_DAX;
> + meta = NULL; /* owned by the inode now */
> + rc = 0;
> + }
> + inode_unlock(inode);
> +
> +out:
> + kvfree(fmap_buf);
> + if (meta)
> + famfs_meta_free(meta);
> + return rc;
> +}
> +
> +/**
> + * famfs_file_ioctl() - Top-level famfs file ioctl handler
> + * @file: the file
> + * @cmd: ioctl opcode
> + * @arg: ioctl opcode argument (if any)
> + */
> +static long
> +famfs_file_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
> +{
> + struct inode *inode = file_inode(file);
> + struct famfs_fs_info *fsi = inode->i_sb->s_fs_info;
> + long rc;
> +
> + if (fsi->deverror && (cmd != FAMFSIOC_NOP))
> + return -ENODEV;
> +
> + switch (cmd) {
> + case FAMFSIOC_NOP:
> + rc = 0;
> + break;
> +
> + case FAMFSIOC_MAP_CREATE:
> + rc = famfs_file_init_dax(file, (void __user *)arg);
> + break;
> +
> + default:
> + rc = -ENOTTY;
> + break;
> + }
> +
> + return rc;
> +}
> +
> /*********************************************************************
> * vm_operations
> */
> @@ -93,9 +397,25 @@ const struct vm_operations_struct famfs_file_vm_ops = {
> static ssize_t
> famfs_file_invalid(struct inode *inode)
> {
> + struct famfs_file_meta *meta = inode->i_private;
> + size_t i_size = i_size_read(inode);
> +
> + if (!meta) {
> + pr_debug("%s: un-initialized famfs file\n", __func__);
> + return -EIO;
> + }
> + if (meta->error) {
> + pr_debug("%s: previously detected metadata errors\n", __func__);
> + return -EIO;
> + }
> + if (i_size != meta->file_size) {
> + pr_warn("%s: i_size overwritten from %ld to %ld\n",
> + __func__, meta->file_size, i_size);
> + meta->error = true;
> + return -ENXIO;
> + }
> if (!IS_DAX(inode)) {
> - pr_debug("%s: inode %llx IS_DAX is false\n",
> - __func__, (u64)inode);
> + pr_debug("%s: inode %llx IS_DAX is false\n", __func__,
> (u64)inode);
> return -ENXIO;
> }
> return 0;
> @@ -222,7 +542,7 @@ const struct file_operations famfs_file_operations = {
> /* Custom famfs operations */
> .write_iter = famfs_dax_write_iter,
> .read_iter = famfs_dax_read_iter,
> - .unlocked_ioctl = NULL /*famfs_file_ioctl*/,
> + .unlocked_ioctl = famfs_file_ioctl,
> .mmap = famfs_file_mmap,
>
> /* Force PMD alignment for mmap */
> diff --git a/fs/famfs/famfs_inode.c b/fs/famfs/famfs_inode.c
> index 910a143dad30..a6c3b4574e69 100644
> --- a/fs/famfs/famfs_inode.c
> +++ b/fs/famfs/famfs_inode.c
> @@ -300,6 +300,7 @@ static int famfs_show_options(struct seq_file *m, struct
> dentry *root)
>
> static void famfs_evict_inode(struct inode *inode)
> {
> + famfs_meta_free((struct famfs_file_meta *)inode->i_private);
> inode->i_private = NULL;
> dax_break_layout_final(inode);
> truncate_inode_pages_final(&inode->i_data);
> diff --git a/fs/famfs/famfs_internal.h b/fs/famfs/famfs_internal.h
> index 26f5abda96dc..b5f9c8d0349f 100644
> --- a/fs/famfs/famfs_internal.h
> +++ b/fs/famfs/famfs_internal.h
> @@ -15,8 +15,52 @@
> #include <linux/bits.h>
> #include <linux/build_bug.h>
>
> +#include <linux/famfs_ioctl.h>
> +
> extern const struct file_operations famfs_file_operations;
>
> +/*
> + * Internal sanity bound on a FAMFSIOC_MAP_CREATE fmap message. The ABI does
> + * not advertise a maximum (the message is self-describing); this only guards
> + * the copy-in against an unreasonable allocation. Oversize is rejected with
> + * -EFBIG.
> + */
> +#define FAMFS_FMAP_MSG_MAX (4 * 1024 * 1024)
> +
> +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 inode->i_private.
> + */
> +struct famfs_file_meta {
> + bool error;
> + enum famfs_file_type file_type;
> + size_t file_size;
> + enum famfs_ioc_ext_type fm_extent_type;
> + u64 dev_bitmap; /* referenced daxdev indices */
> + 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;
> + };
> + };
> +};
> +
> struct famfs_mount_opts {
> umode_t mode;
> };
> @@ -83,4 +127,6 @@ int famfs_devlist_alloc(struct famfs_fs_info *fsi);
> int famfs_install_daxdev(struct famfs_fs_info *fsi, struct super_block *sb,
> u64 index, dev_t devno, const char *name);
>
> +void famfs_meta_free(struct famfs_file_meta *map);
> +
> #endif /* FAMFS_INTERNAL_H */
> diff --git a/include/uapi/linux/famfs_ioctl.h
> b/include/uapi/linux/famfs_ioctl.h
> new file mode 100644
> index 000000000000..b4eb373c1ade
> --- /dev/null
> +++ b/include/uapi/linux/famfs_ioctl.h
> @@ -0,0 +1,91 @@
> +/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
> +/*
> + * famfs - dax file system for shared fabric-attached memory
> + *
> + * Copyright 2023-2024 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.
> + */
> +#ifndef FAMFS_IOCTL_H
> +#define FAMFS_IOCTL_H
> +
> +#include <linux/ioctl.h>
> +#include <linux/uuid.h>
> +
> +#define FAMFS_KABI_VERSION 44
> +
> +enum famfs_file_type {
> + FAMFS_REG,
> + FAMFS_SUPERBLOCK,
> + FAMFS_LOG,
> +};
> +
> +/*
> + * Extent type in a famfs fmap message, and of the in-core map
> + * (famfs_file_meta.fm_extent_type).
> + */
> +enum famfs_ioc_ext_type {
> + FAMFS_IOC_EXT_SIMPLE,
> + FAMFS_IOC_EXT_INTERLEAVE,
> +};
> +
> +/*
> + * The FAMFSIOC_MAP_CREATE payload is a self-describing fmap message: a
> + * struct famfs_ioc_fmap_header immediately followed by @nextents extent
> + * records. @fmap_size gives the total message length, so a reader is
> + * self-delimiting.
> + *
> + * For ext_type == FAMFS_IOC_EXT_SIMPLE the records are an array of
> + * @nextents famfs_ioc_simple_ext. For ext_type == FAMFS_IOC_EXT_INTERLEAVE
> + * each of the @nextents records is a famfs_ioc_iext header immediately
> + * followed by ie_nstrips famfs_ioc_simple_ext strip extents.
> + *
> + * This wire layout is byte-identical to the fmap carried in a fuse famfs
> + * GET_FMAP reply, so the same userspace serializer emits both.
> + *
> + * The message is self-describing (@fmap_size bounds it), so neither the
> extent
> + * and strip counts nor the total size are capped by this ABI. The kernel
> + * applies an internal sanity limit to the copy-in and returns -EFBIG for a
> + * message larger than it will accept.
> + */
> +#define FAMFS_FMAP_VERSION 1
> +
> +struct famfs_ioc_simple_ext {
> + __u32 se_devindex;
> + __u32 reserved;
> + __u64 se_offset;
> + __u64 se_len;
> +};
> +
> +struct famfs_ioc_iext { /* interleaved (striped) extent */
> + __u32 ie_nstrips;
> + __u32 ie_chunk_size;
> + __u64 ie_nbytes; /* total bytes mapped by this interleaved
> extent */
> + __u64 reserved;
> +};
> +
> +struct famfs_ioc_fmap_header {
> + __u8 file_type; /* enum famfs_file_type */
> + __u8 reserved;
> + __u16 fmap_version; /* FAMFS_FMAP_VERSION */
> + __u32 ext_type; /* enum famfs_ioc_ext_type */
> + __u32 nextents;
> + __u32 fmap_size; /* total message bytes, including this header */
> + __u64 file_size;
> + __u64 reserved1;
> +};
> +
> +#define FAMFSIOC_MAGIC 'u'
> +
> +/* famfs file ioctl opcodes */
> +#define FAMFSIOC_NOP _IO(FAMFSIOC_MAGIC, 0x50)
> +
> +/*
> + * MAP_CREATE carries the self-describing fmap message - struct
> + * famfs_ioc_fmap_header followed by the extent list (see above).
> + */
> +#define FAMFSIOC_MAP_CREATE _IOW(FAMFSIOC_MAGIC, 0x51, struct
> famfs_ioc_fmap_header)
> +
> +#endif /* FAMFS_IOCTL_H */
> --
> 2.53.0
>
>
>
