On Wed, 7 Jan 2026 09:33:23 -0600 John Groves <[email protected]> wrote:
> 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 <[email protected]> A few things inline. J > diff --git a/fs/fuse/famfs.c b/fs/fuse/famfs.c > new file mode 100644 > index 000000000000..0f7e3f00e1e7 > --- /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 2023-2025 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/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) > +{ > + struct fuse_inode *fi = get_fuse_inode(inode); > + size_t fmap_bufsize = FMAP_BUFSIZE; > + u64 nodeid = get_node_id(inode); > + ssize_t fmap_size; > + void *fmap_buf; > + int rc; > + > + FUSE_ARGS(args); > + > + /* Don't retrieve if we already have the famfs metadata */ > + if (fi->famfs_meta) > + return 0; > + > + fmap_buf = kcalloc(1, FMAP_BUFSIZE, GFP_KERNEL); If there is only ever 1, does kcalloc() make sense over kzalloc()? > + if (!fmap_buf) > + return -EIO; > + > + args.opcode = FUSE_GET_FMAP; > + args.nodeid = nodeid; > + > + /* Variable-sized output buffer > + * this causes fuse_simple_request() to return the size of the > + * output payload > + */ > + args.out_argvar = true; > + args.out_numargs = 1; > + args.out_args[0].size = fmap_bufsize; > + args.out_args[0].value = fmap_buf; > + > + /* Send GET_FMAP command */ > + rc = fuse_simple_request(fm, &args); > + if (rc < 0) { > + pr_err("%s: err=%d from fuse_simple_request()\n", > + __func__, rc); Leaks the fmap_buf? Maybe use a __free() so no need to keep track of htat. > + return rc; > + } > + 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. > + */ > + > + kfree(fmap_buf); > + return 0; > +} > diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h > index 84d0ee2a501d..691c7850cf4e 100644 > --- a/fs/fuse/fuse_i.h > +++ b/fs/fuse/fuse_i.h > @@ -223,6 +223,14 @@ struct fuse_inode { > > +static inline struct fuse_backing *famfs_meta_set(struct fuse_inode *fi, > + void *meta) > +{ > +#if IS_ENABLED(CONFIG_FUSE_FAMFS_DAX) > + return xchg(&fi->famfs_meta, meta); > +#else > + return NULL; > +#endif > +} > + > +static inline void famfs_meta_free(struct fuse_inode *fi) > +{ > + /* Stub wil be connected in a subsequent commit */ > +} > + > +static inline int fuse_file_famfs(struct fuse_inode *fi) > +{ > +#if IS_ENABLED(CONFIG_FUSE_FAMFS_DAX) > + return (READ_ONCE(fi->famfs_meta) != NULL); > +#else > + return 0; > +#endif > +} > + > +#if IS_ENABLED(CONFIG_FUSE_FAMFS_DAX) > +int fuse_get_fmap(struct fuse_mount *fm, struct inode *inode); > +#else > +static inline int > +fuse_get_fmap(struct fuse_mount *fm, struct inode *inode) > +{ > + return 0; > +} > +#endif I'd do a single block under one if IS_ENABLED() and then use an else for the stubs. Should end up more readable. Jonathan
