linux/fs/vboxsf/file.c

// SPDX-License-Identifier: MIT
/*
 * VirtualBox Guest Shared Folders support: Regular file inode and file ops.
 *
 * Copyright (C) 2006-2018 Oracle Corporation
 */

#include <linux/mm.h>
#include <linux/page-flags.h>
#include <linux/pagemap.h>
#include <linux/highmem.h>
#include <linux/sizes.h>
#include "vfsmod.h"

struct vboxsf_handle { … };

struct vboxsf_handle *vboxsf_create_sf_handle(struct inode *inode,
					      u64 handle, u32 access_flags)
{ … }

static int vboxsf_file_open(struct inode *inode, struct file *file)
{ … }

static void vboxsf_handle_release(struct kref *refcount)
{ … }

void vboxsf_release_sf_handle(struct inode *inode, struct vboxsf_handle *sf_handle)
{ … }

static int vboxsf_file_release(struct inode *inode, struct file *file)
{ … }

/*
 * Write back dirty pages now, because there may not be any suitable
 * open files later
 */
static void vboxsf_vma_close(struct vm_area_struct *vma)
{ … }

static const struct vm_operations_struct vboxsf_file_vm_ops = …;

static int vboxsf_file_mmap(struct file *file, struct vm_area_struct *vma)
{ … }

/*
 * Note that since we are accessing files on the host's filesystem, files
 * may always be changed underneath us by the host!
 *
 * The vboxsf API between the guest and the host does not offer any functions
 * to deal with this. There is no inode-generation to check for changes, no
 * events / callback on changes and no way to lock files.
 *
 * To avoid returning stale data when a file gets *opened* on our (the guest)
 * side, we do a "stat" on the host side, then compare the mtime with the
 * last known mtime and invalidate the page-cache if they differ.
 * This is done from vboxsf_inode_revalidate().
 *
 * When reads are done through the read_iter fop, it is possible to do
 * further cache revalidation then, there are 3 options to deal with this:
 *
 * 1)  Rely solely on the revalidation done at open time
 * 2)  Do another "stat" and compare mtime again. Unfortunately the vboxsf
 *     host API does not allow stat on handles, so we would need to use
 *     file->f_path.dentry and the stat will then fail if the file was unlinked
 *     or renamed (and there is no thing like NFS' silly-rename). So we get:
 * 2a) "stat" and compare mtime, on stat failure invalidate the cache
 * 2b) "stat" and compare mtime, on stat failure do nothing
 * 3)  Simply always call invalidate_inode_pages2_range on the range of the read
 *
 * Currently we are keeping things KISS and using option 1. this allows
 * directly using generic_file_read_iter without wrapping it.
 *
 * This means that only data written on the host side before open() on
 * the guest side is guaranteed to be seen by the guest. If necessary
 * we may provide other read-cache strategies in the future and make this
 * configurable through a mount option.
 */
const struct file_operations vboxsf_reg_fops = …;

const struct inode_operations vboxsf_reg_iops = …;

static int vboxsf_read_folio(struct file *file, struct folio *folio)
{ … }

static struct vboxsf_handle *vboxsf_get_write_handle(struct vboxsf_inode *sf_i)
{ … }

static int vboxsf_writepage(struct page *page, struct writeback_control *wbc)
{ … }

static int vboxsf_write_end(struct file *file, struct address_space *mapping,
			    loff_t pos, unsigned int len, unsigned int copied,
			    struct page *page, void *fsdata)
{ … }

/*
 * Note simple_write_begin does not read the page from disk on partial writes
 * this is ok since vboxsf_write_end only writes the written parts of the
 * page and it does not call SetPageUptodate for partial writes.
 */
const struct address_space_operations vboxsf_reg_aops = …;

static const char *vboxsf_get_link(struct dentry *dentry, struct inode *inode,
				   struct delayed_call *done)
{ … }

const struct inode_operations vboxsf_lnk_iops = …;