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Date: Thu, 28 Mar 2024 18:53:24 -0700
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Subject: [RFC PATCH v4 09/36] fuse-bpf: Add lseek support
From: Daniel Rosenberg <drosen@google.com>
To: Miklos Szeredi <miklos@szeredi.hu>, bpf@vger.kernel.org, 
	Alexei Starovoitov <ast@kernel.org>
Cc: Amir Goldstein <amir73il@gmail.com>, linux-kernel@vger.kernel.org, 
	linux-fsdevel@vger.kernel.org, linux-unionfs@vger.kernel.org, 
	Daniel Borkmann <daniel@iogearbox.net>, John Fastabend <john.fastabend@gmail.com>, 
	Andrii Nakryiko <andrii@kernel.org>, Martin KaFai Lau <martin.lau@linux.dev>, Song Liu <song@kernel.org>, 
	Eduard Zingerman <eddyz87@gmail.com>, Yonghong Song <yonghong.song@linux.dev>, 
	KP Singh <kpsingh@kernel.org>, Stanislav Fomichev <sdf@google.com>, Hao Luo <haoluo@google.com>, 
	Jiri Olsa <jolsa@kernel.org>, Shuah Khan <shuah@kernel.org>, Jonathan Corbet <corbet@lwn.net>, 
	Joanne Koong <joannelkoong@gmail.com>, Mykola Lysenko <mykolal@fb.com>, 
	Christian Brauner <brauner@kernel.org>, kernel-team@android.com, 
	Daniel Rosenberg <drosen@google.com>, Paul Lawrence <paullawrence@google.com>
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This adds backing support for FUSE_LSEEK

Signed-off-by: Daniel Rosenberg <drosen@google.com>
Signed-off-by: Paul Lawrence <paullawrence@google.com>
---
 fs/fuse/backing.c | 89 +++++++++++++++++++++++++++++++++++++++++++++++
 fs/fuse/file.c    |  3 ++
 fs/fuse/fuse_i.h  |  6 ++++
 3 files changed, 98 insertions(+)

diff --git a/fs/fuse/backing.c b/fs/fuse/backing.c
index 331b3f23ef78..04cb0c0c10b0 100644
--- a/fs/fuse/backing.c
+++ b/fs/fuse/backing.c
@@ -210,6 +210,95 @@ static void fuse_stat_to_attr(struct fuse_conn *fc, struct inode *inode,
 	attr->blksize = 1 << blkbits;
 }
 
+struct fuse_lseek_args {
+	struct fuse_lseek_in in;
+	struct fuse_lseek_out out;
+};
+
+static int fuse_lseek_initialize_in(struct bpf_fuse_args *fa, struct fuse_lseek_args *args,
+				    struct file *file, loff_t offset, int whence)
+{
+	struct fuse_file *fuse_file = file->private_data;
+
+	args->in = (struct fuse_lseek_in) {
+		.fh = fuse_file->fh,
+		.offset = offset,
+		.whence = whence,
+	};
+
+	*fa = (struct bpf_fuse_args) {
+		.info = (struct bpf_fuse_meta_info) {
+			.nodeid = get_node_id(file->f_inode),
+			.opcode = FUSE_LSEEK,
+		},
+		.in_numargs = 1,
+		.in_args[0].size = sizeof(args->in),
+		.in_args[0].value = &args->in,
+	};
+
+	return 0;
+}
+
+static int fuse_lseek_initialize_out(struct bpf_fuse_args *fa, struct fuse_lseek_args *args,
+				     struct file *file, loff_t offset, int whence)
+{
+	fa->out_numargs = 1;
+	fa->out_args[0].size = sizeof(args->out);
+	fa->out_args[0].value = &args->out;
+
+	return 0;
+}
+
+static int fuse_lseek_backing(struct bpf_fuse_args *fa, loff_t *out,
+			      struct file *file, loff_t offset, int whence)
+{
+	const struct fuse_lseek_in *fli = fa->in_args[0].value;
+	struct fuse_lseek_out *flo = fa->out_args[0].value;
+	struct fuse_file *fuse_file = file->private_data;
+	struct file *backing_file = fuse_file->backing_file;
+
+	/* TODO: Handle changing of the file handle */
+	if (offset == 0) {
+		if (whence == SEEK_CUR) {
+			flo->offset = file->f_pos;
+			*out = flo->offset;
+			return 0;
+		}
+
+		if (whence == SEEK_SET) {
+			flo->offset = vfs_setpos(file, 0, 0);
+			*out = flo->offset;
+			return 0;
+		}
+	}
+
+	inode_lock(file->f_inode);
+	backing_file->f_pos = file->f_pos;
+	*out = vfs_llseek(backing_file, fli->offset, fli->whence);
+	flo->offset = *out;
+	inode_unlock(file->f_inode);
+	return 0;
+}
+
+static int fuse_lseek_finalize(struct bpf_fuse_args *fa, loff_t *out,
+			       struct file *file, loff_t offset, int whence)
+{
+	struct fuse_lseek_out *flo = fa->out_args[0].value;
+
+	if (!fa->info.error_in)
+		file->f_pos = flo->offset;
+	*out = flo->offset;
+	return 0;
+}
+
+int fuse_bpf_lseek(loff_t *out, struct inode *inode, struct file *file, loff_t offset, int whence)
+{
+	return bpf_fuse_backing(inode, struct fuse_lseek_args, out,
+				fuse_lseek_initialize_in, fuse_lseek_initialize_out,
+				fuse_lseek_backing, fuse_lseek_finalize,
+				file, offset, whence);
+}
+
 ssize_t fuse_backing_mmap(struct file *file, struct vm_area_struct *vma)
 {
 	int ret;
diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index b15a0c30fec8..b3cae6e677f8 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -2740,6 +2740,9 @@ static loff_t fuse_file_llseek(struct file *file, loff_t offset, int whence)
 	loff_t retval;
 	struct inode *inode = file_inode(file);
 
+	if (fuse_bpf_lseek(&retval, inode, file, offset, whence))
+		return retval;
+
 	switch (whence) {
 	case SEEK_SET:
 	case SEEK_CUR:
diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
index 5f76ba3c1e4b..24f453d162ae 100644
--- a/fs/fuse/fuse_i.h
+++ b/fs/fuse/fuse_i.h
@@ -1438,11 +1438,17 @@ int parse_fuse_bpf_entry(struct fuse_bpf_entry *fbe, int num_entries);
 
 #ifdef CONFIG_FUSE_BPF
 
+int fuse_bpf_lseek(loff_t *out, struct inode *inode, struct file *file, loff_t offset, int whence);
 int fuse_bpf_lookup(struct dentry **out, struct inode *dir, struct dentry *entry, unsigned int flags);
 int fuse_bpf_access(int *out, struct inode *inode, int mask);
 
 #else
 
+static inline int fuse_bpf_lseek(loff_t *out, struct inode *inode, struct file *file, loff_t offset, int whence)
+{
+	return 0;
+}
+
 static inline int fuse_bpf_lookup(struct dentry **out, struct inode *dir, struct dentry *entry, unsigned int flags)
 {
 	return 0;
-- 
2.44.0.478.gd926399ef9-goog