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fuse: introduce FUSE_PASSTHROUGH capability 

FUSE_PASSTHROUGH capability to passthrough FUSE operations to backing
files will be made available with kernel config CONFIG_FUSE_PASSTHROUGH.

When requesting FUSE_PASSTHROUGH, userspace needs to specify the
max_stack_depth that is allowed for FUSE on top of backing files.

Introduce the flag FOPEN_PASSTHROUGH and backing_id to fuse_open_out
argument that can be used when replying to OPEN request, to setup
passthrough of io operations on the fuse inode to a backing file.

Introduce a refcounted fuse_backing object that will be used to
associate an open backing file with a fuse inode.

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
This commit is contained in:
Amir Goldstein 2024-02-09 16:57:17 +02:00 committed by Miklos Szeredi
parent aed918310e
commit 7dc4e97a4f
6 changed files with 121 additions and 3 deletions
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11
fs/fuse/Kconfig
View File

@ -52,3 +52,14 @@ config FUSE_DAX
If you want to allow mounting a Virtio Filesystem with the "dax"
option, answer Y.
config FUSE_PASSTHROUGH
bool "FUSE passthrough operations support"
default y
depends on FUSE_FS
select FS_STACK
help
This allows bypassing FUSE server by mapping specific FUSE operations
to be performed directly on a backing file.
If you want to allow passthrough operations, answer Y.

1
fs/fuse/Makefile
View File

@ -10,5 +10,6 @@ obj-$(CONFIG_VIRTIO_FS) += virtiofs.o
fuse-y := dev.o dir.o file.o inode.o control.o xattr.o acl.o readdir.o ioctl.o
fuse-y += iomode.o
fuse-$(CONFIG_FUSE_DAX) += dax.o
fuse-$(CONFIG_FUSE_PASSTHROUGH) += passthrough.o
virtiofs-y := virtio_fs.o

42
fs/fuse/fuse_i.h
View File

@ -76,6 +76,15 @@ struct fuse_submount_lookup {
struct fuse_forget_link *forget;
};
/** Container for data related to mapping to backing file */
struct fuse_backing {
struct file *file;
/** refcount */
refcount_t count;
struct rcu_head rcu;
};
/** FUSE inode */
struct fuse_inode {
/** Inode data */
@ -179,6 +188,10 @@ struct fuse_inode {
#endif
/** Submount specific lookup tracking */
struct fuse_submount_lookup *submount_lookup;
#ifdef CONFIG_FUSE_PASSTHROUGH
/** Reference to backing file in passthrough mode */
struct fuse_backing *fb;
#endif
};
/** FUSE inode state bits */
@ -829,6 +842,12 @@ struct fuse_conn {
/* Is statx not implemented by fs? */
unsigned int no_statx:1;
/** Passthrough support for read/write IO */
unsigned int passthrough:1;
/** Maximum stack depth for passthrough backing files */
int max_stack_depth;
/** The number of requests waiting for completion */
atomic_t num_waiting;
@ -1368,4 +1387,27 @@ struct fuse_file *fuse_file_open(struct fuse_mount *fm, u64 nodeid,
void fuse_file_release(struct inode *inode, struct fuse_file *ff,
unsigned int open_flags, fl_owner_t id, bool isdir);
/* passthrough.c */
static inline struct fuse_backing *fuse_inode_backing(struct fuse_inode *fi)
{
#ifdef CONFIG_FUSE_PASSTHROUGH
return READ_ONCE(fi->fb);
#else
return NULL;
#endif
}
static inline struct fuse_backing *fuse_inode_backing_set(struct fuse_inode *fi,
struct fuse_backing *fb)
{
#ifdef CONFIG_FUSE_PASSTHROUGH
return xchg(&fi->fb, fb);
#else
return NULL;
#endif
}
struct fuse_backing *fuse_backing_get(struct fuse_backing *fb);
void fuse_backing_put(struct fuse_backing *fb);
#endif /* _FS_FUSE_I_H */

26
fs/fuse/inode.c
View File

@ -111,6 +111,9 @@ static struct inode *fuse_alloc_inode(struct super_block *sb)
if (IS_ENABLED(CONFIG_FUSE_DAX) && !fuse_dax_inode_alloc(sb, fi))
goto out_free_forget;
if (IS_ENABLED(CONFIG_FUSE_PASSTHROUGH))
fuse_inode_backing_set(fi, NULL);
return &fi->inode;
out_free_forget:
@ -129,6 +132,9 @@ static void fuse_free_inode(struct inode *inode)
#ifdef CONFIG_FUSE_DAX
kfree(fi->dax);
#endif
if (IS_ENABLED(CONFIG_FUSE_PASSTHROUGH))
fuse_backing_put(fuse_inode_backing(fi));
kmem_cache_free(fuse_inode_cachep, fi);
}
@ -1284,6 +1290,24 @@ static void process_init_reply(struct fuse_mount *fm, struct fuse_args *args,
fc->create_supp_group = 1;
if (flags & FUSE_DIRECT_IO_ALLOW_MMAP)
fc->direct_io_allow_mmap = 1;
/*
* max_stack_depth is the max stack depth of FUSE fs,
* so it has to be at least 1 to support passthrough
* to backing files.
*
* with max_stack_depth > 1, the backing files can be
* on a stacked fs (e.g. overlayfs) themselves and with
* max_stack_depth == 1, FUSE fs can be stacked as the
* underlying fs of a stacked fs (e.g. overlayfs).
*/
if (IS_ENABLED(CONFIG_FUSE_PASSTHROUGH) &&
(flags & FUSE_PASSTHROUGH) &&
arg->max_stack_depth > 0 &&
arg->max_stack_depth <= FILESYSTEM_MAX_STACK_DEPTH) {
fc->passthrough = 1;
fc->max_stack_depth = arg->max_stack_depth;
fm->sb->s_stack_depth = arg->max_stack_depth;
}
} else {
ra_pages = fc->max_read / PAGE_SIZE;
fc->no_lock = 1;
@ -1339,6 +1363,8 @@ void fuse_send_init(struct fuse_mount *fm)
#endif
if (fm->fc->auto_submounts)
flags |= FUSE_SUBMOUNTS;
if (IS_ENABLED(CONFIG_FUSE_PASSTHROUGH))
flags |= FUSE_PASSTHROUGH;
ia->in.flags = flags;
ia->in.flags2 = flags >> 32;

30
fs/fuse/passthrough.c Normal file
View File

@ -0,0 +1,30 @@
// SPDX-License-Identifier: GPL-2.0
/*
* FUSE passthrough to backing file.
*
* Copyright (c) 2023 CTERA Networks.
*/
#include "fuse_i.h"
#include <linux/file.h>
struct fuse_backing *fuse_backing_get(struct fuse_backing *fb)
{
if (fb && refcount_inc_not_zero(&fb->count))
return fb;
return NULL;
}
static void fuse_backing_free(struct fuse_backing *fb)
{
if (fb->file)
fput(fb->file);
kfree_rcu(fb, rcu);
}
void fuse_backing_put(struct fuse_backing *fb)
{
if (fb && refcount_dec_and_test(&fb->count))
fuse_backing_free(fb);
}

14
include/uapi/linux/fuse.h
View File

@ -211,6 +211,10 @@
* 7.39
* - add FUSE_DIRECT_IO_ALLOW_MMAP
* - add FUSE_STATX and related structures
*
* 7.40
* - add max_stack_depth to fuse_init_out, add FUSE_PASSTHROUGH init flag
* - add backing_id to fuse_open_out, add FOPEN_PASSTHROUGH open flag
*/
#ifndef _LINUX_FUSE_H
@ -246,7 +250,7 @@
#define FUSE_KERNEL_VERSION 7
/** Minor version number of this interface */
#define FUSE_KERNEL_MINOR_VERSION 39
#define FUSE_KERNEL_MINOR_VERSION 40
/** The node ID of the root inode */
#define FUSE_ROOT_ID 1
@ -353,6 +357,7 @@ struct fuse_file_lock {
* FOPEN_STREAM: the file is stream-like (no file position at all)
* FOPEN_NOFLUSH: don't flush data cache on close (unless FUSE_WRITEBACK_CACHE)
* FOPEN_PARALLEL_DIRECT_WRITES: Allow concurrent direct writes on the same inode
* FOPEN_PASSTHROUGH: passthrough read/write io for this open file
*/
#define FOPEN_DIRECT_IO (1 << 0)
#define FOPEN_KEEP_CACHE (1 << 1)
@ -361,6 +366,7 @@ struct fuse_file_lock {
#define FOPEN_STREAM (1 << 4)
#define FOPEN_NOFLUSH (1 << 5)
#define FOPEN_PARALLEL_DIRECT_WRITES (1 << 6)
#define FOPEN_PASSTHROUGH (1 << 7)
/**
* INIT request/reply flags
@ -449,6 +455,7 @@ struct fuse_file_lock {
#define FUSE_CREATE_SUPP_GROUP (1ULL << 34)
#define FUSE_HAS_EXPIRE_ONLY (1ULL << 35)
#define FUSE_DIRECT_IO_ALLOW_MMAP (1ULL << 36)
#define FUSE_PASSTHROUGH (1ULL << 37)
/* Obsolete alias for FUSE_DIRECT_IO_ALLOW_MMAP */
#define FUSE_DIRECT_IO_RELAX FUSE_DIRECT_IO_ALLOW_MMAP
@ -761,7 +768,7 @@ struct fuse_create_in {
struct fuse_open_out {
uint64_t fh;
uint32_t open_flags;
uint32_t padding;
int32_t backing_id;
};
struct fuse_release_in {
@ -877,7 +884,8 @@ struct fuse_init_out {
uint16_t max_pages;
uint16_t map_alignment;
uint32_t flags2;
uint32_t unused[7];
uint32_t max_stack_depth;
uint32_t unused[6];
};
#define CUSE_INIT_INFO_MAX 4096