1// SPDX-License-Identifier: MIT
2/*
3 * VirtualBox Guest Shared Folders support: Regular file inode and file ops.
4 *
5 * Copyright (C) 2006-2018 Oracle Corporation
6 */
7
8#include <linux/mm.h>
9#include <linux/page-flags.h>
10#include <linux/pagemap.h>
11#include <linux/highmem.h>
12#include <linux/sizes.h>
13#include "vfsmod.h"
14
15struct vboxsf_handle {
16 u64 handle;
17 u32 root;
18 u32 access_flags;
19 struct kref refcount;
20 struct list_head head;
21};
22
23struct vboxsf_handle *vboxsf_create_sf_handle(struct inode *inode,
24 u64 handle, u32 access_flags)
25{
26 struct vboxsf_inode *sf_i = VBOXSF_I(inode);
27 struct vboxsf_handle *sf_handle;
28
29 sf_handle = kmalloc(size: sizeof(*sf_handle), GFP_KERNEL);
30 if (!sf_handle)
31 return ERR_PTR(error: -ENOMEM);
32
33 /* the host may have given us different attr then requested */
34 sf_i->force_restat = 1;
35
36 /* init our handle struct and add it to the inode's handles list */
37 sf_handle->handle = handle;
38 sf_handle->root = VBOXSF_SBI(inode->i_sb)->root;
39 sf_handle->access_flags = access_flags;
40 kref_init(kref: &sf_handle->refcount);
41
42 mutex_lock(&sf_i->handle_list_mutex);
43 list_add(new: &sf_handle->head, head: &sf_i->handle_list);
44 mutex_unlock(lock: &sf_i->handle_list_mutex);
45
46 return sf_handle;
47}
48
49static int vboxsf_file_open(struct inode *inode, struct file *file)
50{
51 struct vboxsf_sbi *sbi = VBOXSF_SBI(inode->i_sb);
52 struct shfl_createparms params = {};
53 struct vboxsf_handle *sf_handle;
54 u32 access_flags = 0;
55 int err;
56
57 /*
58 * We check the value of params.handle afterwards to find out if
59 * the call succeeded or failed, as the API does not seem to cleanly
60 * distinguish error and informational messages.
61 *
62 * Furthermore, we must set params.handle to SHFL_HANDLE_NIL to
63 * make the shared folders host service use our mode parameter.
64 */
65 params.handle = SHFL_HANDLE_NIL;
66 if (file->f_flags & O_CREAT) {
67 params.create_flags |= SHFL_CF_ACT_CREATE_IF_NEW;
68 /*
69 * We ignore O_EXCL, as the Linux kernel seems to call create
70 * beforehand itself, so O_EXCL should always fail.
71 */
72 if (file->f_flags & O_TRUNC)
73 params.create_flags |= SHFL_CF_ACT_OVERWRITE_IF_EXISTS;
74 else
75 params.create_flags |= SHFL_CF_ACT_OPEN_IF_EXISTS;
76 } else {
77 params.create_flags |= SHFL_CF_ACT_FAIL_IF_NEW;
78 if (file->f_flags & O_TRUNC)
79 params.create_flags |= SHFL_CF_ACT_OVERWRITE_IF_EXISTS;
80 }
81
82 switch (file->f_flags & O_ACCMODE) {
83 case O_RDONLY:
84 access_flags |= SHFL_CF_ACCESS_READ;
85 break;
86
87 case O_WRONLY:
88 access_flags |= SHFL_CF_ACCESS_WRITE;
89 break;
90
91 case O_RDWR:
92 access_flags |= SHFL_CF_ACCESS_READWRITE;
93 break;
94
95 default:
96 WARN_ON(1);
97 }
98
99 if (file->f_flags & O_APPEND)
100 access_flags |= SHFL_CF_ACCESS_APPEND;
101
102 params.create_flags |= access_flags;
103 params.info.attr.mode = inode->i_mode;
104
105 err = vboxsf_create_at_dentry(dentry: file_dentry(file), params: &params);
106 if (err == 0 && params.handle == SHFL_HANDLE_NIL)
107 err = (params.result == SHFL_FILE_EXISTS) ? -EEXIST : -ENOENT;
108 if (err)
109 return err;
110
111 sf_handle = vboxsf_create_sf_handle(inode, handle: params.handle, access_flags);
112 if (IS_ERR(ptr: sf_handle)) {
113 vboxsf_close(root: sbi->root, handle: params.handle);
114 return PTR_ERR(ptr: sf_handle);
115 }
116
117 file->private_data = sf_handle;
118 return 0;
119}
120
121static void vboxsf_handle_release(struct kref *refcount)
122{
123 struct vboxsf_handle *sf_handle =
124 container_of(refcount, struct vboxsf_handle, refcount);
125
126 vboxsf_close(root: sf_handle->root, handle: sf_handle->handle);
127 kfree(objp: sf_handle);
128}
129
130void vboxsf_release_sf_handle(struct inode *inode, struct vboxsf_handle *sf_handle)
131{
132 struct vboxsf_inode *sf_i = VBOXSF_I(inode);
133
134 mutex_lock(&sf_i->handle_list_mutex);
135 list_del(entry: &sf_handle->head);
136 mutex_unlock(lock: &sf_i->handle_list_mutex);
137
138 kref_put(kref: &sf_handle->refcount, release: vboxsf_handle_release);
139}
140
141static int vboxsf_file_release(struct inode *inode, struct file *file)
142{
143 /*
144 * When a file is closed on our (the guest) side, we want any subsequent
145 * accesses done on the host side to see all changes done from our side.
146 */
147 filemap_write_and_wait(mapping: inode->i_mapping);
148
149 vboxsf_release_sf_handle(inode, sf_handle: file->private_data);
150 return 0;
151}
152
153/*
154 * Write back dirty pages now, because there may not be any suitable
155 * open files later
156 */
157static void vboxsf_vma_close(struct vm_area_struct *vma)
158{
159 filemap_write_and_wait(mapping: vma->vm_file->f_mapping);
160}
161
162static const struct vm_operations_struct vboxsf_file_vm_ops = {
163 .close = vboxsf_vma_close,
164 .fault = filemap_fault,
165 .map_pages = filemap_map_pages,
166};
167
168static int vboxsf_file_mmap(struct file *file, struct vm_area_struct *vma)
169{
170 int err;
171
172 err = generic_file_mmap(file, vma);
173 if (!err)
174 vma->vm_ops = &vboxsf_file_vm_ops;
175
176 return err;
177}
178
179/*
180 * Note that since we are accessing files on the host's filesystem, files
181 * may always be changed underneath us by the host!
182 *
183 * The vboxsf API between the guest and the host does not offer any functions
184 * to deal with this. There is no inode-generation to check for changes, no
185 * events / callback on changes and no way to lock files.
186 *
187 * To avoid returning stale data when a file gets *opened* on our (the guest)
188 * side, we do a "stat" on the host side, then compare the mtime with the
189 * last known mtime and invalidate the page-cache if they differ.
190 * This is done from vboxsf_inode_revalidate().
191 *
192 * When reads are done through the read_iter fop, it is possible to do
193 * further cache revalidation then, there are 3 options to deal with this:
194 *
195 * 1) Rely solely on the revalidation done at open time
196 * 2) Do another "stat" and compare mtime again. Unfortunately the vboxsf
197 * host API does not allow stat on handles, so we would need to use
198 * file->f_path.dentry and the stat will then fail if the file was unlinked
199 * or renamed (and there is no thing like NFS' silly-rename). So we get:
200 * 2a) "stat" and compare mtime, on stat failure invalidate the cache
201 * 2b) "stat" and compare mtime, on stat failure do nothing
202 * 3) Simply always call invalidate_inode_pages2_range on the range of the read
203 *
204 * Currently we are keeping things KISS and using option 1. this allows
205 * directly using generic_file_read_iter without wrapping it.
206 *
207 * This means that only data written on the host side before open() on
208 * the guest side is guaranteed to be seen by the guest. If necessary
209 * we may provide other read-cache strategies in the future and make this
210 * configurable through a mount option.
211 */
212const struct file_operations vboxsf_reg_fops = {
213 .llseek = generic_file_llseek,
214 .read_iter = generic_file_read_iter,
215 .write_iter = generic_file_write_iter,
216 .mmap = vboxsf_file_mmap,
217 .open = vboxsf_file_open,
218 .release = vboxsf_file_release,
219 .fsync = noop_fsync,
220 .splice_read = filemap_splice_read,
221 .setlease = simple_nosetlease,
222};
223
224const struct inode_operations vboxsf_reg_iops = {
225 .getattr = vboxsf_getattr,
226 .setattr = vboxsf_setattr
227};
228
229static int vboxsf_read_folio(struct file *file, struct folio *folio)
230{
231 struct page *page = &folio->page;
232 struct vboxsf_handle *sf_handle = file->private_data;
233 loff_t off = page_offset(page);
234 u32 nread = PAGE_SIZE;
235 u8 *buf;
236 int err;
237
238 buf = kmap(page);
239
240 err = vboxsf_read(root: sf_handle->root, handle: sf_handle->handle, offset: off, buf_len: &nread, buf);
241 if (err == 0) {
242 memset(&buf[nread], 0, PAGE_SIZE - nread);
243 flush_dcache_page(page);
244 SetPageUptodate(page);
245 } else {
246 SetPageError(page);
247 }
248
249 kunmap(page);
250 unlock_page(page);
251 return err;
252}
253
254static struct vboxsf_handle *vboxsf_get_write_handle(struct vboxsf_inode *sf_i)
255{
256 struct vboxsf_handle *h, *sf_handle = NULL;
257
258 mutex_lock(&sf_i->handle_list_mutex);
259 list_for_each_entry(h, &sf_i->handle_list, head) {
260 if (h->access_flags == SHFL_CF_ACCESS_WRITE ||
261 h->access_flags == SHFL_CF_ACCESS_READWRITE) {
262 kref_get(kref: &h->refcount);
263 sf_handle = h;
264 break;
265 }
266 }
267 mutex_unlock(lock: &sf_i->handle_list_mutex);
268
269 return sf_handle;
270}
271
272static int vboxsf_writepage(struct page *page, struct writeback_control *wbc)
273{
274 struct inode *inode = page->mapping->host;
275 struct vboxsf_inode *sf_i = VBOXSF_I(inode);
276 struct vboxsf_handle *sf_handle;
277 loff_t off = page_offset(page);
278 loff_t size = i_size_read(inode);
279 u32 nwrite = PAGE_SIZE;
280 u8 *buf;
281 int err;
282
283 if (off + PAGE_SIZE > size)
284 nwrite = size & ~PAGE_MASK;
285
286 sf_handle = vboxsf_get_write_handle(sf_i);
287 if (!sf_handle)
288 return -EBADF;
289
290 buf = kmap(page);
291 err = vboxsf_write(root: sf_handle->root, handle: sf_handle->handle,
292 offset: off, buf_len: &nwrite, buf);
293 kunmap(page);
294
295 kref_put(kref: &sf_handle->refcount, release: vboxsf_handle_release);
296
297 if (err == 0) {
298 ClearPageError(page);
299 /* mtime changed */
300 sf_i->force_restat = 1;
301 } else {
302 ClearPageUptodate(page);
303 }
304
305 unlock_page(page);
306 return err;
307}
308
309static int vboxsf_write_end(struct file *file, struct address_space *mapping,
310 loff_t pos, unsigned int len, unsigned int copied,
311 struct page *page, void *fsdata)
312{
313 struct inode *inode = mapping->host;
314 struct vboxsf_handle *sf_handle = file->private_data;
315 unsigned int from = pos & ~PAGE_MASK;
316 u32 nwritten = len;
317 u8 *buf;
318 int err;
319
320 /* zero the stale part of the page if we did a short copy */
321 if (!PageUptodate(page) && copied < len)
322 zero_user(page, start: from + copied, size: len - copied);
323
324 buf = kmap(page);
325 err = vboxsf_write(root: sf_handle->root, handle: sf_handle->handle,
326 offset: pos, buf_len: &nwritten, buf: buf + from);
327 kunmap(page);
328
329 if (err) {
330 nwritten = 0;
331 goto out;
332 }
333
334 /* mtime changed */
335 VBOXSF_I(inode)->force_restat = 1;
336
337 if (!PageUptodate(page) && nwritten == PAGE_SIZE)
338 SetPageUptodate(page);
339
340 pos += nwritten;
341 if (pos > inode->i_size)
342 i_size_write(inode, i_size: pos);
343
344out:
345 unlock_page(page);
346 put_page(page);
347
348 return nwritten;
349}
350
351/*
352 * Note simple_write_begin does not read the page from disk on partial writes
353 * this is ok since vboxsf_write_end only writes the written parts of the
354 * page and it does not call SetPageUptodate for partial writes.
355 */
356const struct address_space_operations vboxsf_reg_aops = {
357 .read_folio = vboxsf_read_folio,
358 .writepage = vboxsf_writepage,
359 .dirty_folio = filemap_dirty_folio,
360 .write_begin = simple_write_begin,
361 .write_end = vboxsf_write_end,
362};
363
364static const char *vboxsf_get_link(struct dentry *dentry, struct inode *inode,
365 struct delayed_call *done)
366{
367 struct vboxsf_sbi *sbi = VBOXSF_SBI(inode->i_sb);
368 struct shfl_string *path;
369 char *link;
370 int err;
371
372 if (!dentry)
373 return ERR_PTR(error: -ECHILD);
374
375 path = vboxsf_path_from_dentry(sbi, dentry);
376 if (IS_ERR(ptr: path))
377 return ERR_CAST(ptr: path);
378
379 link = kzalloc(PATH_MAX, GFP_KERNEL);
380 if (!link) {
381 __putname(path);
382 return ERR_PTR(error: -ENOMEM);
383 }
384
385 err = vboxsf_readlink(root: sbi->root, parsed_path: path, PATH_MAX, buf: link);
386 __putname(path);
387 if (err) {
388 kfree(objp: link);
389 return ERR_PTR(error: err);
390 }
391
392 set_delayed_call(call: done, fn: kfree_link, arg: link);
393 return link;
394}
395
396const struct inode_operations vboxsf_lnk_iops = {
397 .get_link = vboxsf_get_link
398};
399

source code of linux/fs/vboxsf/file.c