Commit 7dc4e97a authored by Amir Goldstein's avatar Amir Goldstein Committed by Miklos Szeredi
Browse files

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: default avatarAmir Goldstein <amir73il@gmail.com>
Signed-off-by: default avatarMiklos Szeredi <mszeredi@redhat.com>
parent aed91831

fs/fuse/Kconfig

+11 −0
Original line number Diff line number Diff line
@@ -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.

fs/fuse/Makefile

+1 −0
Original line number Diff line number Diff line
@@ -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

fs/fuse/fuse_i.h

+42 −0
Original line number Diff line number Diff line
@@ -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 */

fs/fuse/inode.c

+26 −0
Original line number Diff line number Diff line
@@ -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;

fs/fuse/passthrough.c

0 → 100644
+30 −0
Original line number Diff line number Diff line 
// 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);

}