linux/fs/fuse/passthrough.c

// SPDX-License-Identifier: GPL-2.0
/*
 * FUSE passthrough to backing file.
 *
 * Copyright (c) 2023 CTERA Networks.
 */

#include "fuse_i.h"

#include <linux/file.h>
#include <linux/backing-file.h>
#include <linux/splice.h>

static void fuse_file_accessed(struct file *file)
{
	struct inode *inode = file_inode(file);

	fuse_invalidate_atime(inode);
}

static void fuse_passthrough_end_write(struct kiocb *iocb, ssize_t ret)
{
	struct inode *inode = file_inode(iocb->ki_filp);

	fuse_write_update_attr(inode, iocb->ki_pos, ret);
}

ssize_t fuse_passthrough_read_iter(struct kiocb *iocb, struct iov_iter *iter)
{
	struct file *file = iocb->ki_filp;
	struct fuse_file *ff = file->private_data;
	struct file *backing_file = fuse_file_passthrough(ff);
	size_t count = iov_iter_count(iter);
	ssize_t ret;
	struct backing_file_ctx ctx = {
		.cred = ff->cred,
		.accessed = fuse_file_accessed,
	};


	pr_debug("%s: backing_file=0x%p, pos=%lld, len=%zu\n", __func__,
		 backing_file, iocb->ki_pos, count);

	if (!count)
		return 0;

	ret = backing_file_read_iter(backing_file, iter, iocb, iocb->ki_flags,
				     &ctx);

	return ret;
}

ssize_t fuse_passthrough_write_iter(struct kiocb *iocb,
				    struct iov_iter *iter)
{
	struct file *file = iocb->ki_filp;
	struct inode *inode = file_inode(file);
	struct fuse_file *ff = file->private_data;
	struct file *backing_file = fuse_file_passthrough(ff);
	size_t count = iov_iter_count(iter);
	ssize_t ret;
	struct backing_file_ctx ctx = {
		.cred = ff->cred,
		.end_write = fuse_passthrough_end_write,
	};

	pr_debug("%s: backing_file=0x%p, pos=%lld, len=%zu\n", __func__,
		 backing_file, iocb->ki_pos, count);

	if (!count)
		return 0;

	inode_lock(inode);
	ret = backing_file_write_iter(backing_file, iter, iocb, iocb->ki_flags,
				      &ctx);
	inode_unlock(inode);

	return ret;
}

ssize_t fuse_passthrough_splice_read(struct file *in, loff_t *ppos,
				     struct pipe_inode_info *pipe,
				     size_t len, unsigned int flags)
{
	struct fuse_file *ff = in->private_data;
	struct file *backing_file = fuse_file_passthrough(ff);
	struct backing_file_ctx ctx = {
		.cred = ff->cred,
		.accessed = fuse_file_accessed,
	};
	struct kiocb iocb;
	ssize_t ret;

	pr_debug("%s: backing_file=0x%p, pos=%lld, len=%zu, flags=0x%x\n", __func__,
		 backing_file, *ppos, len, flags);

	init_sync_kiocb(&iocb, in);
	iocb.ki_pos = *ppos;
	ret = backing_file_splice_read(backing_file, &iocb, pipe, len, flags, &ctx);
	*ppos = iocb.ki_pos;

	return ret;
}

ssize_t fuse_passthrough_splice_write(struct pipe_inode_info *pipe,
				      struct file *out, loff_t *ppos,
				      size_t len, unsigned int flags)
{
	struct fuse_file *ff = out->private_data;
	struct file *backing_file = fuse_file_passthrough(ff);
	struct inode *inode = file_inode(out);
	ssize_t ret;
	struct backing_file_ctx ctx = {
		.cred = ff->cred,
		.end_write = fuse_passthrough_end_write,
	};
	struct kiocb iocb;

	pr_debug("%s: backing_file=0x%p, pos=%lld, len=%zu, flags=0x%x\n", __func__,
		 backing_file, *ppos, len, flags);

	inode_lock(inode);
	init_sync_kiocb(&iocb, out);
	iocb.ki_pos = *ppos;
	ret = backing_file_splice_write(pipe, backing_file, &iocb, len, flags, &ctx);
	*ppos = iocb.ki_pos;
	inode_unlock(inode);

	return ret;
}

ssize_t fuse_passthrough_mmap(struct file *file, struct vm_area_struct *vma)
{
	struct fuse_file *ff = file->private_data;
	struct file *backing_file = fuse_file_passthrough(ff);
	struct backing_file_ctx ctx = {
		.cred = ff->cred,
		.accessed = fuse_file_accessed,
	};

	pr_debug("%s: backing_file=0x%p, start=%lu, end=%lu\n", __func__,
		 backing_file, vma->vm_start, vma->vm_end);

	return backing_file_mmap(backing_file, vma, &ctx);
}

/*
 * Setup passthrough to a backing file.
 *
 * Returns an fb object with elevated refcount to be stored in fuse inode.
 */
struct fuse_backing *fuse_passthrough_open(struct file *file, int backing_id)
{
	struct fuse_file *ff = file->private_data;
	struct fuse_conn *fc = ff->fm->fc;
	struct fuse_backing *fb = NULL;
	struct file *backing_file;
	int err;

	err = -EINVAL;
	if (backing_id <= 0)
		goto out;

	err = -ENOENT;
	fb = fuse_backing_lookup(fc, backing_id);
	if (!fb)
		goto out;

	/* Allocate backing file per fuse file to store fuse path */
	backing_file = backing_file_open(&file->f_path, file->f_flags,
					 &fb->file->f_path, fb->cred);
	err = PTR_ERR(backing_file);
	if (IS_ERR(backing_file)) {
		fuse_backing_put(fb);
		goto out;
	}

	err = 0;
	ff->passthrough = backing_file;
	ff->cred = get_cred(fb->cred);
out:
	pr_debug("%s: backing_id=%d, fb=0x%p, backing_file=0x%p, err=%i\n", __func__,
		 backing_id, fb, ff->passthrough, err);

	return err ? ERR_PTR(err) : fb;
}

void fuse_passthrough_release(struct fuse_file *ff, struct fuse_backing *fb)
{
	pr_debug("%s: fb=0x%p, backing_file=0x%p\n", __func__,
		 fb, ff->passthrough);

	fput(ff->passthrough);
	ff->passthrough = NULL;
	put_cred(ff->cred);
	ff->cred = NULL;
}