Re: [RFC PATCH v2 04/21] fuse: Add fuse-bpf, a stacked fs extension for FUSE

Amir Goldstein
2022-11-22T10:21:38Z

On Tue, Nov 22, 2022 at 4:16 AM Daniel Rosenberg <drosen@google.com> wrote:
>
> Fuse-bpf provides a short circuit path for Fuse implementations that act
> as a stacked filesystem. For cases that are directly unchanged,
> operations are passed directly to the backing filesystem. Small
> adjustments can be handled by bpf prefilters or postfilters, with the
> option to fall back to userspace as needed.
>
> Fuse implementations may supply backing node information, as well as bpf
> programs via an optional add on to the lookup structure.
>
> This has been split over the next set of patches for readability.
> Clusters of fuse ops have been split into their own patches, as well as
> the actual bpf calls and userspace calls for filters.
>
> Signed-off-by: Daniel Rosenberg <drosen@google.com>
> Signed-off-by: Paul Lawrence <paullawrence@google.com>
> Signed-off-by: Alessio Balsini <balsini@google.com>
> ---
> fs/fuse/Kconfig | 8 +
> fs/fuse/Makefile | 1 +
> fs/fuse/backing.c | 392 ++++++++++++++++++++++++++++++++++++++++++++++
> fs/fuse/dev.c | 41 ++++-
> fs/fuse/dir.c | 187 +++++++++++++++++-----
> fs/fuse/file.c | 25 ++-
> fs/fuse/fuse_i.h | 99 +++++++++++-
> fs/fuse/inode.c | 189 +++++++++++++++++-----
> fs/fuse/ioctl.c | 2 +-
> 9 files changed, 861 insertions(+), 83 deletions(-)
> create mode 100644 fs/fuse/backing.c
>
> diff --git a/fs/fuse/Kconfig b/fs/fuse/Kconfig
> index 038ed0b9aaa5..3a64fa73e591 100644
> --- a/fs/fuse/Kconfig
> +++ b/fs/fuse/Kconfig
> @@ -52,3 +52,11 @@ config FUSE_DAX
>
> If you want to allow mounting a Virtio Filesystem with the "dax"
> option, answer Y.
> +
> +config FUSE_BPF
> + bool "Adds BPF to fuse"
> + depends on FUSE_FS
> + depends on BPF
> + help
> + Extends FUSE by adding BPF to prefilter calls and potentially pass to a
> + backing file system
> diff --git a/fs/fuse/Makefile b/fs/fuse/Makefile
> index 0c48b35c058d..a0853c439db2 100644
> --- a/fs/fuse/Makefile
> +++ b/fs/fuse/Makefile
> @@ -9,5 +9,6 @@ obj-$(CONFIG_VIRTIO_FS) += virtiofs.o
>
> fuse-y := dev.o dir.o file.o inode.o control.o xattr.o acl.o readdir.o ioctl.o
> fuse-$(CONFIG_FUSE_DAX) += dax.o
> +fuse-$(CONFIG_FUSE_BPF) += backing.o
>
> virtiofs-y := virtio_fs.o
> diff --git a/fs/fuse/backing.c b/fs/fuse/backing.c
> new file mode 100644
> index 000000000000..5a59a8963d52
> --- /dev/null
> +++ b/fs/fuse/backing.c
> @@ -0,0 +1,392 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * FUSE-BPF: Filesystem in Userspace with BPF
> + * Copyright (c) 2021 Google LLC
> + */
> +
> +#include "fuse_i.h"
> +
> +#include <linux/fdtable.h>
> +#include <linux/file.h>
> +#include <linux/fs_stack.h>
> +#include <linux/namei.h>
> +
> +/*
> + * expression statement to wrap the backing filter logic
> + * struct inode *inode: inode with bpf and backing inode
> + * typedef io: (typically complex) type whose components fuse_args can point to.
> + * An instance of this type is created locally and passed to initialize
> + * void initialize_in(struct fuse_args *fa, io *in_out, args...): function that sets
> + * up fa and io based on args
> + * void initialize_out(struct fuse_args *fa, io *in_out, args...): function that sets
> + * up fa and io based on args
> + * int backing(struct fuse_bpf_args_internal *fa, args...): function that actually performs
> + * the backing io operation
> + * void *finalize(struct fuse_bpf_args *, args...): function that performs any final
> + * work needed to commit the backing io
> + */
> +#define fuse_bpf_backing(inode, io, out, initialize_in, initialize_out, \
> + backing, finalize, args...) \
> +({ \
> + struct fuse_inode *fuse_inode = get_fuse_inode(inode); \
> + struct fuse_args fa = { 0 }; \
> + bool initialized = false; \
> + bool handled = false; \
> + ssize_t res; \
> + io feo = { 0 }; \
> + int error = 0; \
> + \
> + do { \
> + if (!fuse_inode || !fuse_inode->backing_inode) \
> + break; \
> + \
> + handled = true; \
> + error = initialize_in(&fa, &feo, args); \
> + if (error) \
> + break; \
> + \
> + error = initialize_out(&fa, &feo, args); \
> + if (error) \
> + break; \
> + \
> + initialized = true; \
> + \
> + error = backing(&fa, out, args); \
> + if (error < 0) \
> + fa.error_in = error; \
> + \
> + } while (false); \
> + \
> + if (initialized && handled) { \
> + res = finalize(&fa, out, args); \
> + if (res) \
> + error = res; \
> + } \
> + \
> + *out = error ? _Generic((*out), \
> + default : \
> + error, \
> + struct dentry * : \
> + ERR_PTR(error), \
> + const char * : \
> + ERR_PTR(error) \
> + ) : (*out); \
> + handled; \
> +})
> +

I hope there is a better way than this macro...
Haven't studied the patches enough to be able to suggest one.

Thanks,
Amir.