[RFC PATCH v3 12/37] fuse-bpf: Partially add mapping support

[Daniel Rosenberg <drosen@xxxxxxxxxx>]

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@xxxxxxxxxx>
Signed-off-by: Paul Lawrence <paullawrence@xxxxxxxxxx>
---
 fs/fuse/backing.c | 37 +++++++++++++++++++++++++++++++++++++
 fs/fuse/file.c    |  6 ++++++
 fs/fuse/fuse_i.h  |  4 +++-
 3 files changed, 46 insertions(+), 1 deletion(-)

diff --git a/fs/fuse/backing.c b/fs/fuse/backing.c
index e42622584037..930aa370e376 100644
--- a/fs/fuse/backing.c
+++ b/fs/fuse/backing.c
@@ -207,6 +207,43 @@ 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);
+
+	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;
+
+	if ((!timespec64_equal(&fuse_inode->i_mtime, &backing_inode->i_mtime) ||
+	     !timespec64_equal(&fuse_inode->i_ctime,
+			       &backing_inode->i_ctime))) {
+		fuse_inode->i_mtime = backing_inode->i_mtime;
+		fuse_inode->i_ctime = backing_inode->i_ctime;
+	}
+	touch_atime(&file->f_path);
+
+	return ret;
+}
+
 /*******************************************************************************
  * Directory operations after here                                             *
  ******************************************************************************/
diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index 25fb49f0a9f7..865167a80d35 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -2527,6 +2527,12 @@ 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 (vma->vm_flags & VM_MAYSHARE)
diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
index cb166168f9c2..5eb357f482dc 100644
--- a/fs/fuse/fuse_i.h
+++ b/fs/fuse/fuse_i.h
@@ -1422,7 +1422,9 @@ 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);
 
-- 
2.40.0.634.g4ca3ef3211-goog