// 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;
}