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

[Amir Goldstein <amir73il@gmail.com>]

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.