Re: [PATCH V7 12/19] famfs_fuse: Plumb the GET_FMAP message/response

John Groves
2026-02-26T00:24:36Z

On 26/02/19 10:12AM, Dave Jiang wrote:
>
>
> On 1/18/26 3:33 PM, John Groves wrote:
> > From: John Groves <john@groves.net>
> >
> > Upon completion of an OPEN, if we're in famfs-mode we do a GET_FMAP to
> > retrieve and cache up the file-to-dax map in the kernel. If this
> > succeeds, read/write/mmap are resolved direct-to-dax with no upcalls.
> >
> > Signed-off-by: John Groves <john@groves.net>
> > ---
> > MAINTAINERS | 8 +++++
> > fs/fuse/Makefile | 1 +
> > fs/fuse/famfs.c | 74 +++++++++++++++++++++++++++++++++++++++
> > fs/fuse/file.c | 14 +++++++-
> > fs/fuse/fuse_i.h | 70 +++++++++++++++++++++++++++++++++---
> > fs/fuse/inode.c | 8 ++++-
> > fs/fuse/iomode.c | 2 +-
> > include/uapi/linux/fuse.h | 7 ++++
> > 8 files changed, 176 insertions(+), 8 deletions(-)
> > create mode 100644 fs/fuse/famfs.c
> >
> > diff --git a/MAINTAINERS b/MAINTAINERS
> > index 10aa5120d93f..e3d0aa5eb361 100644
> > --- a/MAINTAINERS
> > +++ b/MAINTAINERS
> > @@ -10379,6 +10379,14 @@ F: fs/fuse/
> > F: include/uapi/linux/fuse.h
> > F: tools/testing/selftests/filesystems/fuse/
> >
> > +FUSE [FAMFS Fabric-Attached Memory File System]
> > +M: John Groves <jgroves@micron.com>
> > +M: John Groves <John@Groves.net>
> > +L: linux-cxl@vger.kernel.org
> > +L: linux-fsdevel@vger.kernel.org
> > +S: Supported
> > +F: fs/fuse/famfs.c
> > +
> > FUTEX SUBSYSTEM
> > M: Thomas Gleixner <tglx@kernel.org>
> > M: Ingo Molnar <mingo@redhat.com>
> > diff --git a/fs/fuse/Makefile b/fs/fuse/Makefile
> > index 22ad9538dfc4..3f8dcc8cbbd0 100644
> > --- a/fs/fuse/Makefile
> > +++ b/fs/fuse/Makefile
> > @@ -17,5 +17,6 @@ fuse-$(CONFIG_FUSE_DAX) += dax.o
> > fuse-$(CONFIG_FUSE_PASSTHROUGH) += passthrough.o backing.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..615819cc922d
> > --- /dev/null
> > +++ b/fs/fuse/famfs.c
> > @@ -0,0 +1,74 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +/*
> > + * famfs - dax file system for shared fabric-attached memory
> > + *
> > + * Copyright 2023-2026 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/cleanup.h>
> > +#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 "fuse_i.h"
> > +
> > +
> > +#define FMAP_BUFSIZE PAGE_SIZE
> > +
> > +int
> > +fuse_get_fmap(struct fuse_mount *fm, struct inode *inode)
>
> keep the return int on the same line?

Done, thanks

>
> > +{
> > + void *fmap_buf __free(kfree) = NULL;
>
> Should do the variable declaration when you do the kzalloc(). That way you can avoid any potential use before check issues.

Done, thanks

>
> > + struct fuse_inode *fi = get_fuse_inode(inode);
> > + size_t fmap_bufsize = FMAP_BUFSIZE;
> > + u64 nodeid = get_node_id(inode);
> > + ssize_t fmap_size;
> > + int rc;
> > +
> > + FUSE_ARGS(args);
> > +
> > + /* Don't retrieve if we already have the famfs metadata */
> > + if (fi->famfs_meta)
> > + return 0;
> > +
> > + fmap_buf = kzalloc(FMAP_BUFSIZE, GFP_KERNEL);
> > + if (!fmap_buf)
> > + return -EIO;
>
> -ENOMEM?
>
> DJ

Done, thanks!

John