b5a001d7af762bf3a7349ff1c9805be64a1ff8c66d3e6bf26079810e.patch

From 811c87ff46bffcf4875d2d5b997c936155511d29 Mon Sep 17 00:00:00 2001
From: Alessio Balsini <balsini@google.com>
Date: Mon, 25 Jan 2021 17:02:28 +0000
Subject: [PATCH] FROMLIST: fuse: Definitions and ioctl for passthrough

Expose the FUSE_PASSTHROUGH interface to user space and declare all the
basic data structures and functions as the skeleton on top of which the
FUSE passthrough functionality will be built.

As part of this, introduce the new FUSE passthrough ioctl, which allows
the FUSE daemon to specify a direct connection between a FUSE file and a
lower file system file. Such ioctl requires user space to pass the file
descriptor of one of its opened files through the fuse_passthrough_out
data structure introduced in this patch. This structure includes extra
fields for possible future extensions.
Also, add the passthrough functions for the set-up and tear-down of the
data structures and locks that will be used both when fuse_conns and
fuse_files are created/deleted.

[CPNOTE: 20/05/21] Lee: Still fresh - hopefully this will land upstream soon

Bug: 168023149
Link: https://lore.kernel.org/lkml/20210125153057.3623715-4-balsini@android.com/
Signed-off-by: Alessio Balsini <balsini@android.com>
Change-Id: I732532581348adadda5b5048a9346c2b0868d539
Signed-off-by: Alessio Balsini <balsini@google.com>

[rebase515(groeck):
  Squashed:
    CHROMIUM: fuse: Drop unused variable
]
Signed-off-by: Guenter Roeck <groeck@chromium.org>

Change-Id: Id0ba00c88c8acc92c640369fc87d41c11f32b8d2
---
 fs/fuse/Makefile          |  1 +
 fs/fuse/dir.c             |  2 ++
 fs/fuse/file.c            |  4 +++-
 fs/fuse/fuse_i.h          | 27 +++++++++++++++++++++++++++
 fs/fuse/inode.c           | 16 ++++++++++++++++
 fs/fuse/passthrough.c     | 21 +++++++++++++++++++++
 include/uapi/linux/fuse.h | 11 ++++++++++-
 7 files changed, 80 insertions(+), 2 deletions(-)
 create mode 100644 fs/fuse/passthrough.c

diff --git a/fs/fuse/Makefile b/fs/fuse/Makefile
--- a/fs/fuse/Makefile
+++ b/fs/fuse/Makefile
@@ -8,6 +8,7 @@ obj-$(CONFIG_CUSE) += cuse.o
 obj-$(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 += passthrough.o
 fuse-$(CONFIG_FUSE_DAX) += dax.o
 
 virtiofs-y := virtio_fs.o
diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c
--- a/fs/fuse/dir.c
+++ b/fs/fuse/dir.c
@@ -527,6 +527,7 @@ static int fuse_create_open(struct inode *dir, struct dentry *entry,
 {
 	int err;
 	struct inode *inode;
+	struct fuse_conn *fc = get_fuse_conn(dir);
 	struct fuse_mount *fm = get_fuse_mount(dir);
 	FUSE_ARGS(args);
 	struct fuse_forget_link *forget;
@@ -603,6 +604,7 @@ static int fuse_create_open(struct inode *dir, struct dentry *entry,
 	ff->fh = outopen.fh;
 	ff->nodeid = outentry.nodeid;
 	ff->open_flags = outopen.open_flags;
+	fuse_passthrough_setup(fc, ff, &outopen);
 	inode = fuse_iget(dir->i_sb, outentry.nodeid, outentry.generation,
 			  &outentry.attr, entry_attr_timeout(&outentry), 0);
 	if (!inode) {
diff --git a/fs/fuse/file.c b/fs/fuse/file.c
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -146,7 +146,7 @@ struct fuse_file *fuse_file_open(struct fuse_mount *fm, u64 nodeid,
 		if (!err) {
 			ff->fh = outarg.fh;
 			ff->open_flags = outarg.open_flags;
-
+			fuse_passthrough_setup(fc, ff, &outarg);
 		} else if (err != -ENOSYS) {
 			fuse_file_free(ff);
 			return ERR_PTR(err);
@@ -304,6 +304,8 @@ void fuse_file_release(struct inode *inode, struct fuse_file *ff,
 	struct fuse_release_args *ra = ff->release_args;
 	int opcode = isdir ? FUSE_RELEASEDIR : FUSE_RELEASE;
 
+	fuse_passthrough_release(&ff->passthrough);
+
 	fuse_prepare_release(fi, ff, open_flags, opcode);
 
 	if (ff->flock) {
diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
--- a/fs/fuse/fuse_i.h
+++ b/fs/fuse/fuse_i.h
@@ -173,6 +173,14 @@ struct fuse_conn;
 struct fuse_mount;
 struct fuse_release_args;
 
+/**
+ * Reference to lower filesystem file for read/write operations handled in
+ * passthrough mode
+ */
+struct fuse_passthrough {
+	struct file *filp;
+};
+
 /** FUSE specific file data */
 struct fuse_file {
 	/** Fuse connection for this file */
@@ -218,6 +226,9 @@ struct fuse_file {
 
 	} readdir;
 
+	/** Container for data related to the passthrough functionality */
+	struct fuse_passthrough passthrough;
+
 	/** RB node to be linked on fuse_conn->polled_files */
 	struct rb_node polled_node;
 
@@ -774,6 +785,9 @@ struct fuse_conn {
 	/* Auto-mount submounts announced by the server */
 	unsigned int auto_submounts:1;
 
+	/** Passthrough mode for read/write IO */
+	unsigned int passthrough:1;
+
 	/* Propagate syncfs() to server */
 	unsigned int sync_fs:1;
 
@@ -832,6 +846,12 @@ struct fuse_conn {
 
 	/* New writepages go into this bucket */
 	struct fuse_sync_bucket __rcu *curr_bucket;
+
+	/** IDR for passthrough requests */
+	struct idr passthrough_req;
+
+	/** Protects passthrough_req */
+	spinlock_t passthrough_req_lock;
 };
 
 /*
@@ -1315,4 +1335,11 @@ 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 */
+int fuse_passthrough_open(struct fuse_dev *fud,
+			  struct fuse_passthrough_out *pto);
+int fuse_passthrough_setup(struct fuse_conn *fc, struct fuse_file *ff,
+			   struct fuse_open_out *openarg);
+void fuse_passthrough_release(struct fuse_passthrough *passthrough);
+
 #endif /* _FS_FUSE_I_H */
diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
--- a/fs/fuse/inode.c
+++ b/fs/fuse/inode.c
@@ -814,6 +814,7 @@ void fuse_conn_init(struct fuse_conn *fc, struct fuse_mount *fm,
 	memset(fc, 0, sizeof(*fc));
 	spin_lock_init(&fc->lock);
 	spin_lock_init(&fc->bg_lock);
+	spin_lock_init(&fc->passthrough_req_lock);
 	init_rwsem(&fc->killsb);
 	refcount_set(&fc->count, 1);
 	atomic_set(&fc->dev_count, 1);
@@ -822,6 +823,7 @@ void fuse_conn_init(struct fuse_conn *fc, struct fuse_mount *fm,
 	INIT_LIST_HEAD(&fc->bg_queue);
 	INIT_LIST_HEAD(&fc->entry);
 	INIT_LIST_HEAD(&fc->devices);
+	idr_init(&fc->passthrough_req);
 	atomic_set(&fc->num_waiting, 0);
 	fc->max_background = FUSE_DEFAULT_MAX_BACKGROUND;
 	fc->congestion_threshold = FUSE_DEFAULT_CONGESTION_THRESHOLD;
@@ -1186,6 +1188,12 @@ static void process_init_reply(struct fuse_mount *fm, struct fuse_args *args,
 				fc->handle_killpriv_v2 = 1;
 				fm->sb->s_flags |= SB_NOSEC;
 			}
+			if (flags & FUSE_PASSTHROUGH) {
+				fc->passthrough = 1;
+				/* Prevent further stacking */
+				fm->sb->s_stack_depth =
+					FILESYSTEM_MAX_STACK_DEPTH;
+			}
 			if (flags & FUSE_SETXATTR_EXT)
 				fc->setxattr_ext = 1;
 			if (flags & FUSE_SECURITY_CTX)
@@ -1234,6 +1242,7 @@ void fuse_send_init(struct fuse_mount *fm)
 		FUSE_PARALLEL_DIROPS | FUSE_HANDLE_KILLPRIV | FUSE_POSIX_ACL |
 		FUSE_ABORT_ERROR | FUSE_MAX_PAGES | FUSE_CACHE_SYMLINKS |
 		FUSE_NO_OPENDIR_SUPPORT | FUSE_EXPLICIT_INVAL_DATA |
+		FUSE_PASSTHROUGH |
 		FUSE_HANDLE_KILLPRIV_V2 | FUSE_SETXATTR_EXT | FUSE_INIT_EXT |
 		FUSE_SECURITY_CTX;
 #ifdef CONFIG_FUSE_DAX
@@ -1268,9 +1277,16 @@ void fuse_send_init(struct fuse_mount *fm)
 }
 EXPORT_SYMBOL_GPL(fuse_send_init);
 
+static int free_fuse_passthrough(int id, void *p, void *data)
+{
+	return 0;
+}
+
 void fuse_free_conn(struct fuse_conn *fc)
 {
 	WARN_ON(!list_empty(&fc->devices));
+	idr_for_each(&fc->passthrough_req, free_fuse_passthrough, NULL);
+	idr_destroy(&fc->passthrough_req);
 	kfree_rcu(fc, rcu);
 }
 EXPORT_SYMBOL_GPL(fuse_free_conn);
diff --git a/fs/fuse/passthrough.c b/fs/fuse/passthrough.c
new file mode 100644
--- /dev/null
+++ b/fs/fuse/passthrough.c
@@ -0,0 +1,21 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include "fuse_i.h"
+
+#include <linux/fuse.h>
+
+int fuse_passthrough_open(struct fuse_dev *fud,
+			  struct fuse_passthrough_out *pto)
+{
+	return -EINVAL;
+}
+
+int fuse_passthrough_setup(struct fuse_conn *fc, struct fuse_file *ff,
+			   struct fuse_open_out *openarg)
+{
+	return -EINVAL;
+}
+
+void fuse_passthrough_release(struct fuse_passthrough *passthrough)
+{
+}
diff --git a/include/uapi/linux/fuse.h b/include/uapi/linux/fuse.h
--- a/include/uapi/linux/fuse.h
+++ b/include/uapi/linux/fuse.h
@@ -389,6 +389,7 @@ struct fuse_file_lock {
 /* bits 32..63 get shifted down 32 bits into the flags2 field */
 #define FUSE_SECURITY_CTX	(1ULL << 32)
 #define FUSE_HAS_INODE_DAX	(1ULL << 33)
+#define FUSE_PASSTHROUGH	(1ULL << 34)
 
 /**
  * CUSE INIT request/reply flags
@@ -663,7 +664,7 @@ struct fuse_create_in {
 struct fuse_open_out {
 	uint64_t	fh;
 	uint32_t	open_flags;
-	uint32_t	padding;
+	uint32_t	passthrough_fh;
 };
 
 struct fuse_release_in {
@@ -873,6 +874,13 @@ struct fuse_in_header {
 	uint32_t	padding;
 };
 
+struct fuse_passthrough_out {
+	uint32_t	fd;
+	/* For future implementation */
+	uint32_t	len;
+	void		*vec;
+};
+
 struct fuse_out_header {
 	uint32_t	len;
 	int32_t		error;
@@ -953,6 +961,7 @@ struct fuse_notify_retrieve_in {
 /* Device ioctls: */
 #define FUSE_DEV_IOC_MAGIC		229
 #define FUSE_DEV_IOC_CLONE		_IOR(FUSE_DEV_IOC_MAGIC, 0, uint32_t)
+#define FUSE_DEV_IOC_PASSTHROUGH_OPEN	_IOW(FUSE_DEV_IOC_MAGIC, 1, struct fuse_passthrough_out)
 
 struct fuse_lseek_in {
 	uint64_t	fh;
-- 
2.35.0.rc0.227.g00780c9af4-goog