[PATCH v2 02/21] fuse: prepare for passthrough of inode operations

[Joanne Koong <joannelkoong@gmail.com>]

From: Amir Goldstein <amir73il@gmail.com>

So far, fuse passthrough was implemented for read/write/splice/mmap
operations for regular files opened with FOPEN_PASSTHROUGH.

A backing file is attached to a fuse inode, but only for as long as
there are FOPEN_PASSTHROUGH files opened on this inode.

We would like to attach a backing file to fuse inode also without an
open file to allow passthrough of some inode operations.

Add field ops_mask to the input argument of FUSE_DEV_IOC_BACKING_OPEN
ioctl to declare the operations that would passthrough to the backing
file once it has been attached to the fuse inode on lookup.

Setting the FUSE_READ/FUSE_WRITE operations in the ops_mask is not
required because those operations are implied by FOPEN_PASSTHROUGH.

When setting operations other than FUSE_READ/FUSE_WRITE in ops_mask,
non-regular backing files are allowed, so we need to verify when
attaching a backing file to a fuse inode, that their file types match.

For simplification of inode attribute caching, for now, require a
filesystem with FUSE_PASSTHROUGH_INO (one-to-one mapping from fuse inode
to backing inode) for setting up passthrough of any inode operations.
We may consider relaxing this requirement for some inode operations
in the future.

Reviewed-by: Joanne Koong <joannelkoong@gmail.com>
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
---
 fs/fuse/backing.c         | 13 ++++++++++---
 fs/fuse/fuse_i.h          | 30 ++++++++++++++++++++++++++++++
 fs/fuse/iomode.c          | 16 ++++++++++++++++
 include/uapi/linux/fuse.h |  9 ++++++++-
 4 files changed, 64 insertions(+), 4 deletions(-)

diff --git a/fs/fuse/backing.c b/fs/fuse/backing.c
index 3d3f49c2dd42..1fbb4d876eec 100644
--- a/fs/fuse/backing.c
+++ b/fs/fuse/backing.c
@@ -87,7 +87,8 @@ int fuse_backing_open(struct fuse_conn *fc, struct fuse_backing_map *map)
 	struct fuse_backing *fb = NULL;
 	int res;
 
-	pr_debug("%s: fd=%d flags=0x%x\n", __func__, map->fd, map->flags);
+	pr_debug("%s: fd=%d flags=0x%x ops_mask=0x%llx\n", __func__,
+		 map->fd, map->flags, map->ops_mask);
 
 	/* TODO: relax CAP_SYS_ADMIN once backing files are visible to lsof */
 	res = -EPERM;
@@ -95,7 +96,11 @@ int fuse_backing_open(struct fuse_conn *fc, struct fuse_backing_map *map)
 		goto out;
 
 	res = -EINVAL;
-	if (map->flags || map->padding)
+	if (map->flags || map->ops_mask & ~FUSE_BACKING_MAP_VALID_OPS)
+		goto out;
+
+	/* For now passthrough inode operations requires FUSE_PASSTHROUGH_INO */
+	if (!fc->passthrough_ino && map->ops_mask & FUSE_PASSTHROUGH_INODE_OPS)
 		goto out;
 
 	file = fget_raw(map->fd);
@@ -105,7 +110,8 @@ int fuse_backing_open(struct fuse_conn *fc, struct fuse_backing_map *map)
 
 	/* read/write/splice/mmap passthrough only relevant for regular files */
 	res = d_is_dir(file->f_path.dentry) ? -EISDIR : -EINVAL;
-	if (!d_is_reg(file->f_path.dentry))
+	if (!(map->ops_mask & ~FUSE_PASSTHROUGH_RW_OPS) &&
+	    !d_is_reg(file->f_path.dentry))
 		goto out_fput;
 
 	backing_sb = file_inode(file)->i_sb;
@@ -120,6 +126,7 @@ int fuse_backing_open(struct fuse_conn *fc, struct fuse_backing_map *map)
 
 	fb->file = file;
 	fb->cred = prepare_creds();
+	fb->ops_mask = map->ops_mask;
 	refcount_set(&fb->count, 1);
 
 	res = fuse_backing_id_alloc(fc, fb);
diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
index 0b925ac3e195..8e54dc7d56af 100644
--- a/fs/fuse/fuse_i.h
+++ b/fs/fuse/fuse_i.h
@@ -92,6 +92,7 @@ struct fuse_submount_lookup {
 struct fuse_backing {
 	struct file *file;
 	struct cred *cred;
+	u64 ops_mask;
 
 	/* refcount */
 	refcount_t count;
@@ -254,6 +255,8 @@ enum {
 	 * or the fuse server has an exclusive "lease" on distributed fs
 	 */
 	FUSE_I_EXCLUSIVE,
+	/* Has backing file for inode ops passthrough */
+	FUSE_I_PASSTHROUGH,
 };
 
 struct fuse_conn;
@@ -1252,6 +1255,25 @@ 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 */
+
+/* READ/WRITE are implied by FOPEN_PASSTHROUGH, but defined for completeness */
+#define FUSE_PASSTHROUGH_RW_OPS \
+	(FUSE_PASSTHROUGH_OP_READ | FUSE_PASSTHROUGH_OP_WRITE)
+
+/* File passthrough operations require a file opened with FOPEN_PASSTHROUGH */
+#define FUSE_PASSTHROUGH_FILE_OPS \
+	(FUSE_PASSTHROUGH_RW_OPS)
+
+/* Inode passthrough operations for backing file attached to inode */
+#define FUSE_PASSTHROUGH_INODE_OPS (0)
+
+#define FUSE_BACKING_MAP_OP(map, op) \
+	((map)->ops_mask & FUSE_PASSTHROUGH_OP(op))
+
+#define FUSE_BACKING_MAP_VALID_OPS \
+	(FUSE_PASSTHROUGH_FILE_OPS | FUSE_PASSTHROUGH_INODE_OPS)
+
 /* backing.c */
 #ifdef CONFIG_FUSE_PASSTHROUGH
 struct fuse_backing *fuse_backing_get(struct fuse_backing *fb);
@@ -1319,6 +1341,14 @@ ssize_t fuse_passthrough_splice_write(struct pipe_inode_info *pipe,
 				      size_t len, unsigned int flags);
 ssize_t fuse_passthrough_mmap(struct file *file, struct vm_area_struct *vma);
 
+static inline bool fuse_passthrough_op(struct inode *inode, enum fuse_opcode op)
+{
+	struct fuse_inode *fi = get_fuse_inode(inode);
+	struct fuse_backing *fb = fuse_inode_backing(fi);
+
+	return fb && fb->ops_mask & FUSE_PASSTHROUGH_OP(op);
+}
+
 #ifdef CONFIG_SYSCTL
 extern int fuse_sysctl_register(void);
 extern void fuse_sysctl_unregister(void);
diff --git a/fs/fuse/iomode.c b/fs/fuse/iomode.c
index ca3b28597722..5517711a3eca 100644
--- a/fs/fuse/iomode.c
+++ b/fs/fuse/iomode.c
@@ -96,6 +96,11 @@ int fuse_inode_uncached_io_start(struct inode *inode, struct fuse_backing *fb)
 		err = -EBUSY;
 		goto unlock;
 	}
+	/* fuse and backing file types must match */
+	if (fb && ((fb->file->f_inode->i_mode ^ inode->i_mode) & S_IFMT)) {
+		err = -EIO;
+		goto unlock;
+	}
 	/* With FUSE_PASSTHROUGH_INO, fuse and backing ino must match */
 	if (fb && fc->passthrough_ino &&
 	    fb->file->f_inode->i_ino != inode->i_ino) {
@@ -176,6 +181,7 @@ static int fuse_file_passthrough_open(struct inode *inode, struct file *file)
 {
 	struct fuse_file *ff = file->private_data;
 	struct fuse_conn *fc = get_fuse_conn(inode);
+	struct fuse_inode *fi = get_fuse_inode(inode);
 	struct fuse_backing *fb;
 	int err;
 
@@ -188,11 +194,21 @@ static int fuse_file_passthrough_open(struct inode *inode, struct file *file)
 	if (IS_ERR(fb))
 		return PTR_ERR(fb);
 
+	/*
+	 * Inode ops passthrough requires backing file setup at
+	 * creation/lookup time.
+	 */
+	err = -EOPNOTSUPP;
+	if (!fuse_inode_backing(fi) &&
+	    (fb->ops_mask & FUSE_PASSTHROUGH_INODE_OPS))
+		goto fail;
+
 	/* First passthrough file open denies caching inode io mode */
 	err = fuse_file_uncached_io_open(inode, ff, fb);
 	if (!err)
 		return 0;
 
+fail:
 	fuse_passthrough_release(ff, fb);
 	fuse_backing_put(fb);
 
diff --git a/include/uapi/linux/fuse.h b/include/uapi/linux/fuse.h
index 4be9ccc5b3ff..0f1e1c1ec367 100644
--- a/include/uapi/linux/fuse.h
+++ b/include/uapi/linux/fuse.h
@@ -243,6 +243,7 @@
  *
  *  7.46
  *  - add FUSE_PASSTHROUGH_INO
+ *  - add ops_mask field to struct fuse_backing_map
  */
 
 #ifndef _LINUX_FUSE_H
@@ -1133,9 +1134,15 @@ struct fuse_notify_prune_out {
 struct fuse_backing_map {
 	int32_t		fd;
 	uint32_t	flags;
-	uint64_t	padding;
+	uint64_t	ops_mask;
 };
 
+#define FUSE_PASSTHROUGH_OP(op)	(1ULL << ((op) - 1))
+
+/* op bits for fuse_backing_map ops_mask */
+#define FUSE_PASSTHROUGH_OP_READ	FUSE_PASSTHROUGH_OP(FUSE_READ)
+#define FUSE_PASSTHROUGH_OP_WRITE	FUSE_PASSTHROUGH_OP(FUSE_WRITE)
+
 /* Device ioctls: */
 #define FUSE_DEV_IOC_MAGIC		229
 #define FUSE_DEV_IOC_CLONE		_IOR(FUSE_DEV_IOC_MAGIC, 0, uint32_t)
-- 
2.52.0