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Message-ID: <7jcdlgo7nddrm7phuhj37q2cwgmdal2es6qgswu4fu5sgpgc7v@dt7ltedbjhkq>
Date: Fri, 9 Jan 2026 08:30:39 -0600
From: John Groves <John@...ves.net>
To: Jonathan Cameron <jonathan.cameron@...wei.com>
Cc: Miklos Szeredi <miklos@...redi.hu>,
Dan Williams <dan.j.williams@...el.com>, Bernd Schubert <bschubert@....com>,
Alison Schofield <alison.schofield@...el.com>, John Groves <jgroves@...ron.com>,
Jonathan Corbet <corbet@....net>, Vishal Verma <vishal.l.verma@...el.com>,
Dave Jiang <dave.jiang@...el.com>, Matthew Wilcox <willy@...radead.org>, Jan Kara <jack@...e.cz>,
Alexander Viro <viro@...iv.linux.org.uk>, David Hildenbrand <david@...nel.org>,
Christian Brauner <brauner@...nel.org>, "Darrick J . Wong" <djwong@...nel.org>,
Randy Dunlap <rdunlap@...radead.org>, Jeff Layton <jlayton@...nel.org>,
Amir Goldstein <amir73il@...il.com>, Stefan Hajnoczi <shajnocz@...hat.com>,
Joanne Koong <joannelkoong@...il.com>, Josef Bacik <josef@...icpanda.com>,
Bagas Sanjaya <bagasdotme@...il.com>, Chen Linxuan <chenlinxuan@...ontech.com>,
James Morse <james.morse@....com>, Fuad Tabba <tabba@...gle.com>,
Sean Christopherson <seanjc@...gle.com>, Shivank Garg <shivankg@....com>,
Ackerley Tng <ackerleytng@...gle.com>, Gregory Price <gourry@...rry.net>,
Aravind Ramesh <arramesh@...ron.com>, Ajay Joshi <ajayjoshi@...ron.com>, venkataravis@...ron.com,
linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org, nvdimm@...ts.linux.dev,
linux-cxl@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH V3 15/21] famfs_fuse: Create files with famfs fmaps
On 26/01/08 01:14PM, Jonathan Cameron wrote:
> On Wed, 7 Jan 2026 09:33:24 -0600
> John Groves <John@...ves.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...
> >
> > * 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 files.
> >
> > Signed-off-by: John Groves <john@...ves.net>
>
> > diff --git a/fs/fuse/famfs.c b/fs/fuse/famfs.c
> > index 0f7e3f00e1e7..2aabd1d589fd 100644
> > --- a/fs/fuse/famfs.c
> > +++ b/fs/fuse/famfs.c
> > @@ -17,9 +17,355 @@
> > #include <linux/namei.h>
> > #include <linux/string.h>
> >
> > +#include "famfs_kfmap.h"
> > #include "fuse_i.h"
> >
> >
> > +/***************************************************************************/
> Who doesn't like stars? Why have them here?
>
> > +
> > +void
> > +__famfs_meta_free(void *famfs_meta)
>
> Maybe a local convention, but if not one line.
> Same for other cases.
Done
>
> > +{
> > + struct famfs_file_meta *fmap = famfs_meta;
> > +
> > + if (!fmap)
> > + return;
> > +
> > + if (fmap) {
>
> Well that's never going to fail given 2 lines above.
Good eye. Thanks.
>
>
> > + 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);
> > +}
>
> > +/**
> > + * famfs_fuse_meta_alloc() - Allocate famfs file metadata
> > + * @metap: Pointer to an mcache_map_meta pointer
> > + * @ext_count: The number of extents needed
>
> run kernel-doc over the file as that's not the parameters...
Not sure how I managed that; Fixed, thanks!
>
> > + *
> > + * 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;
>
> void * so cast not needed and hence just assign it at the
> declaration.
Indeed, thanks.
>
> > +
> > + /* 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);
>
> Maybe sprinkle some __free magic on this then you can return in
> all the goto error_out places which to me makes this more readable.
I like it, and I learned how to make __famfs_meta_free() into a
__free() handler.
Done
>
> > + 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);
>
> void * so no need for cast. Though you could keep the cast but apply it to
> fmh + 1 to take advantage of that type.
done, thanks
>
>
> > +
> > + /* 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);
>
> void * so no cast needed.
Right, thanks
>
> > +
> > + /* 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);
> no cast needed.
Done, thanks
>
> > +
> > + /* 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);
>
> Align all lines after 1st one to same point.
Yeah
>
> ...
>
> > +
> > +/**
> > + * 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 = 0;
>
> Always set before use.
Roger that - and it went away with the __free thingy anyway
>
> > +
> > + 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 (fi->famfs_meta) {
> > + rc = -EEXIST; /* file already has famfs metadata */
> > + } else {
> > + if (famfs_meta_set(fi, meta) != NULL) {
> > + pr_debug("%s: file already had metadata\n", __func__);
> > + __famfs_meta_free(meta);
> > + /* rc is 0 - the file is valid */
> > + goto unlock_out;
> > + }
> > + i_size_write(inode, meta->file_size);
> > + inode->i_flags |= S_DAX;
> > + }
> > + unlock_out:
> > + inode_unlock(inode);
> > +
> > +errout:
> > + if (rc)
> > + __famfs_meta_free(meta);
>
> For readability I'd split he good and bad exit paths even it unlock
> needs to happen in two places.
Done
>
>
> > +
> > + return rc;
> > +}
> > +
>
> > diff --git a/fs/fuse/famfs_kfmap.h b/fs/fuse/famfs_kfmap.h
> > new file mode 100644
> > index 000000000000..058645cb10a1
> > --- /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 2023-2025 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.
>
> bonus space after in
Removed
>
> > + *
> > + * 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)
> > + */
>
> > +/*
> > + * 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 */
>
> Not sure what the comment is for. I'd drop it.
I'm sure it made sense to me at some point but not now. Gone.
>
>
> > + 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 */
Thanks!
John
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