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Date: Thu, 28 Mar 2024 18:53:23 -0700
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Subject: [RFC PATCH v4 08/36] fuse-bpf: Partially add mapping 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 a backing implementation for mapping, but is not currently
hooked into the infrastructure that will call the bpf programs.

Signed-off-by: Daniel Rosenberg <drosen@google.com>
Signed-off-by: Paul Lawrence <paullawrence@google.com>
---
 fs/fuse/backing.c | 41 +++++++++++++++++++++++++++++++++++++++++
 fs/fuse/file.c    |  6 ++++++
 fs/fuse/fuse_i.h  |  4 +++-
 3 files changed, 50 insertions(+), 1 deletion(-)

diff --git a/fs/fuse/backing.c b/fs/fuse/backing.c
index a94d99ff9862..331b3f23ef78 100644
--- a/fs/fuse/backing.c
+++ b/fs/fuse/backing.c
@@ -210,6 +210,47 @@ static void fuse_stat_to_attr(struct fuse_conn *fc, struct inode *inode,
 	attr->blksize = 1 << blkbits;
 }
 
+ssize_t fuse_backing_mmap(struct file *file, struct vm_area_struct *vma)
+{
+	int ret;
+	struct fuse_file *ff = file->private_data;
+	struct inode *fuse_inode = file_inode(file);
+	struct file *backing_file = ff->backing_file;
+	struct inode *backing_inode = file_inode(backing_file);
+	struct timespec64 mtime, bmtime, ctime, bctime;
+
+	if (!backing_file->f_op->mmap)
+		return -ENODEV;
+
+	if (WARN_ON(file != vma->vm_file))
+		return -EIO;
+
+	vma->vm_file = get_file(backing_file);
+
+	ret = call_mmap(vma->vm_file, vma);
+
+	if (ret)
+		fput(backing_file);
+	else
+		fput(file);
+
+	if (file->f_flags & O_NOATIME)
+		return ret;
+
+	mtime = inode_get_mtime(fuse_inode);
+	bmtime = inode_get_mtime(backing_inode);
+	ctime = inode_get_ctime(fuse_inode);
+	bctime = inode_get_ctime(backing_inode);
+	if ((!timespec64_equal(&mtime, &bmtime) ||
+	     !timespec64_equal(&ctime, &bctime))) {
+		inode_set_mtime_to_ts(fuse_inode, bmtime);
+		inode_set_ctime_to_ts(fuse_inode, bctime);
+	}
+	touch_atime(&file->f_path);
+
+	return ret;
+}
+
 /*******************************************************************************
  * Directory operations after here                                             *
  ******************************************************************************/
diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index 41a2e88e8646..b15a0c30fec8 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -2486,6 +2486,12 @@ static int fuse_file_mmap(struct file *file, struct vm_area_struct *vma)
 	if (FUSE_IS_DAX(file_inode(file)))
 		return fuse_dax_mmap(file, vma);
 
+#ifdef CONFIG_FUSE_BPF
+	/* TODO - this is simply passthrough, not a proper BPF filter */
+	if (ff->backing_file)
+		return fuse_backing_mmap(file, vma);
+#endif
+
 	if (ff->open_flags & FOPEN_DIRECT_IO) {
 		/* Can't provide the coherency needed for MAP_SHARED
 		 * if FUSE_DIRECT_IO_ALLOW_MMAP isn't set.
diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
index 08ee98b7bb95..5f76ba3c1e4b 100644
--- a/fs/fuse/fuse_i.h
+++ b/fs/fuse/fuse_i.h
@@ -1455,7 +1455,9 @@ static inline int fuse_bpf_access(int *out, struct inode *inode, int mask)
 
 #endif // CONFIG_FUSE_BPF
 
-int fuse_handle_backing(struct fuse_bpf_entry *feb, struct path *backing_path);
+ssize_t fuse_backing_mmap(struct file *file, struct vm_area_struct *vma);
+
+int fuse_handle_backing(struct fuse_bpf_entry *fbe, struct path *backing_path);
 
 int fuse_revalidate_backing(struct dentry *entry, unsigned int flags);
 
-- 
2.44.0.478.gd926399ef9-goog