backing-file.c

  1// SPDX-License-Identifier: GPL-2.0-only
  2/*
  3 * Common helpers for stackable filesystems and backing files.
  4 *
  5 * Forked from fs/overlayfs/file.c.
  6 *
  7 * Copyright (C) 2017 Red Hat, Inc.
  8 * Copyright (C) 2023 CTERA Networks.
  9 */
 10
 11#include <linux/fs.h>
 12#include <linux/backing-file.h>
 13#include <linux/splice.h>
 14#include <linux/mm.h>
 15
 16#include "internal.h"
 17
 18/**
 19 * backing_file_open - open a backing file for kernel internal use
 20 * @user_path:	path that the user reuqested to open
 21 * @flags:	open flags
 22 * @real_path:	path of the backing file
 23 * @cred:	credentials for open
 24 *
 25 * Open a backing file for a stackable filesystem (e.g., overlayfs).
 26 * @user_path may be on the stackable filesystem and @real_path on the
 27 * underlying filesystem.  In this case, we want to be able to return the
 28 * @user_path of the stackable filesystem. This is done by embedding the
 29 * returned file into a container structure that also stores the stacked
 30 * file's path, which can be retrieved using backing_file_user_path().
 31 */
 32struct file *backing_file_open(const struct path *user_path, int flags,
 33			       const struct path *real_path,
 34			       const struct cred *cred)
 35{
 36	struct file *f;
 37	int error;
 38
 39	f = alloc_empty_backing_file(flags, cred);
 40	if (IS_ERR(f))
 41		return f;
 42
 43	path_get(user_path);
 44	backing_file_set_user_path(f, user_path);
 45	error = vfs_open(real_path, f);
 46	if (error) {
 47		fput(f);
 48		f = ERR_PTR(error);
 49	}
 50
 51	return f;
 52}
 53EXPORT_SYMBOL_GPL(backing_file_open);
 54
 55struct file *backing_tmpfile_open(const struct path *user_path, int flags,
 56				  const struct path *real_parentpath,
 57				  umode_t mode, const struct cred *cred)
 58{
 59	struct mnt_idmap *real_idmap = mnt_idmap(real_parentpath->mnt);
 60	struct file *f;
 61	int error;
 62
 63	f = alloc_empty_backing_file(flags, cred);
 64	if (IS_ERR(f))
 65		return f;
 66
 67	path_get(user_path);
 68	backing_file_set_user_path(f, user_path);
 69	error = vfs_tmpfile(real_idmap, real_parentpath, f, mode);
 70	if (error) {
 71		fput(f);
 72		f = ERR_PTR(error);
 73	}
 74	return f;
 75}
 76EXPORT_SYMBOL(backing_tmpfile_open);
 77
 78struct backing_aio {
 79	struct kiocb iocb;
 80	refcount_t ref;
 81	struct kiocb *orig_iocb;
 82	/* used for aio completion */
 83	void (*end_write)(struct kiocb *iocb, ssize_t);
 84	struct work_struct work;
 85	long res;
 86};
 87
 88static struct kmem_cache *backing_aio_cachep;
 89
 90#define BACKING_IOCB_MASK \
 91	(IOCB_NOWAIT | IOCB_HIPRI | IOCB_DSYNC | IOCB_SYNC | IOCB_APPEND)
 92
 93static rwf_t iocb_to_rw_flags(int flags)
 94{
 95	return (__force rwf_t)(flags & BACKING_IOCB_MASK);
 96}
 97
 98static void backing_aio_put(struct backing_aio *aio)
 99{
100	if (refcount_dec_and_test(&aio->ref)) {
101		fput(aio->iocb.ki_filp);
102		kmem_cache_free(backing_aio_cachep, aio);
103	}
104}
105
106static void backing_aio_cleanup(struct backing_aio *aio, long res)
107{
108	struct kiocb *iocb = &aio->iocb;
109	struct kiocb *orig_iocb = aio->orig_iocb;
110
111	orig_iocb->ki_pos = iocb->ki_pos;
112	if (aio->end_write)
113		aio->end_write(orig_iocb, res);
114
115	backing_aio_put(aio);
116}
117
118static void backing_aio_rw_complete(struct kiocb *iocb, long res)
119{
120	struct backing_aio *aio = container_of(iocb, struct backing_aio, iocb);
121	struct kiocb *orig_iocb = aio->orig_iocb;
122
123	if (iocb->ki_flags & IOCB_WRITE)
124		kiocb_end_write(iocb);
125
126	backing_aio_cleanup(aio, res);
127	orig_iocb->ki_complete(orig_iocb, res);
128}
129
130static void backing_aio_complete_work(struct work_struct *work)
131{
132	struct backing_aio *aio = container_of(work, struct backing_aio, work);
133
134	backing_aio_rw_complete(&aio->iocb, aio->res);
135}
136
137static void backing_aio_queue_completion(struct kiocb *iocb, long res)
138{
139	struct backing_aio *aio = container_of(iocb, struct backing_aio, iocb);
140
141	/*
142	 * Punt to a work queue to serialize updates of mtime/size.
143	 */
144	aio->res = res;
145	INIT_WORK(&aio->work, backing_aio_complete_work);
146	queue_work(file_inode(aio->orig_iocb->ki_filp)->i_sb->s_dio_done_wq,
147		   &aio->work);
148}
149
150static int backing_aio_init_wq(struct kiocb *iocb)
151{
152	struct super_block *sb = file_inode(iocb->ki_filp)->i_sb;
153
154	if (sb->s_dio_done_wq)
155		return 0;
156
157	return sb_init_dio_done_wq(sb);
158}
159
160static int do_backing_file_read_iter(struct file *file, struct iov_iter *iter,
161				     struct kiocb *iocb, int flags)
162{
163	struct backing_aio *aio = NULL;
164	int ret;
165
166	if (is_sync_kiocb(iocb)) {
167		rwf_t rwf = iocb_to_rw_flags(flags);
168
169		return vfs_iter_read(file, iter, &iocb->ki_pos, rwf);
170	}
171
172	aio = kmem_cache_zalloc(backing_aio_cachep, GFP_KERNEL);
173	if (!aio)
174		return -ENOMEM;
175
176	aio->orig_iocb = iocb;
177	kiocb_clone(&aio->iocb, iocb, get_file(file));
178	aio->iocb.ki_complete = backing_aio_rw_complete;
179	refcount_set(&aio->ref, 2);
180	ret = vfs_iocb_iter_read(file, &aio->iocb, iter);
181	backing_aio_put(aio);
182	if (ret != -EIOCBQUEUED)
183		backing_aio_cleanup(aio, ret);
184	return ret;
185}
186
187ssize_t backing_file_read_iter(struct file *file, struct iov_iter *iter,
188			       struct kiocb *iocb, int flags,
189			       struct backing_file_ctx *ctx)
190{
191	ssize_t ret;
192
193	if (WARN_ON_ONCE(!(file->f_mode & FMODE_BACKING)))
194		return -EIO;
195
196	if (!iov_iter_count(iter))
197		return 0;
198
199	if (iocb->ki_flags & IOCB_DIRECT &&
200	    !(file->f_mode & FMODE_CAN_ODIRECT))
201		return -EINVAL;
202
203	scoped_with_creds(ctx->cred)
204		ret = do_backing_file_read_iter(file, iter, iocb, flags);
205
206	if (ctx->accessed)
207		ctx->accessed(iocb->ki_filp);
208
209	return ret;
210}
211EXPORT_SYMBOL_GPL(backing_file_read_iter);
212
213static int do_backing_file_write_iter(struct file *file, struct iov_iter *iter,
214				      struct kiocb *iocb, int flags,
215				      void (*end_write)(struct kiocb *, ssize_t))
216{
217	struct backing_aio *aio;
218	int ret;
219
220	if (is_sync_kiocb(iocb)) {
221		rwf_t rwf = iocb_to_rw_flags(flags);
222
223		ret = vfs_iter_write(file, iter, &iocb->ki_pos, rwf);
224		if (end_write)
225			end_write(iocb, ret);
226		return ret;
227	}
228
229	ret = backing_aio_init_wq(iocb);
230	if (ret)
231		return ret;
232
233	aio = kmem_cache_zalloc(backing_aio_cachep, GFP_KERNEL);
234	if (!aio)
235		return -ENOMEM;
236
237	aio->orig_iocb = iocb;
238	aio->end_write = end_write;
239	kiocb_clone(&aio->iocb, iocb, get_file(file));
240	aio->iocb.ki_flags = flags;
241	aio->iocb.ki_complete = backing_aio_queue_completion;
242	refcount_set(&aio->ref, 2);
243	ret = vfs_iocb_iter_write(file, &aio->iocb, iter);
244	backing_aio_put(aio);
245	if (ret != -EIOCBQUEUED)
246		backing_aio_cleanup(aio, ret);
247	return ret;
248}
249
250ssize_t backing_file_write_iter(struct file *file, struct iov_iter *iter,
251				struct kiocb *iocb, int flags,
252				struct backing_file_ctx *ctx)
253{
254	ssize_t ret;
255
256	if (WARN_ON_ONCE(!(file->f_mode & FMODE_BACKING)))
257		return -EIO;
258
259	if (!iov_iter_count(iter))
260		return 0;
261
262	ret = file_remove_privs(iocb->ki_filp);
263	if (ret)
264		return ret;
265
266	if (iocb->ki_flags & IOCB_DIRECT &&
267	    !(file->f_mode & FMODE_CAN_ODIRECT))
268		return -EINVAL;
269
270	scoped_with_creds(ctx->cred)
271		return do_backing_file_write_iter(file, iter, iocb, flags, ctx->end_write);
272}
273EXPORT_SYMBOL_GPL(backing_file_write_iter);
274
275ssize_t backing_file_splice_read(struct file *in, struct kiocb *iocb,
276				 struct pipe_inode_info *pipe, size_t len,
277				 unsigned int flags,
278				 struct backing_file_ctx *ctx)
279{
280	ssize_t ret;
281
282	if (WARN_ON_ONCE(!(in->f_mode & FMODE_BACKING)))
283		return -EIO;
284
285	scoped_with_creds(ctx->cred)
286		ret = vfs_splice_read(in, &iocb->ki_pos, pipe, len, flags);
287
288	if (ctx->accessed)
289		ctx->accessed(iocb->ki_filp);
290
291	return ret;
292}
293EXPORT_SYMBOL_GPL(backing_file_splice_read);
294
295ssize_t backing_file_splice_write(struct pipe_inode_info *pipe,
296				  struct file *out, struct kiocb *iocb,
297				  size_t len, unsigned int flags,
298				  struct backing_file_ctx *ctx)
299{
300	ssize_t ret;
301
302	if (WARN_ON_ONCE(!(out->f_mode & FMODE_BACKING)))
303		return -EIO;
304
305	if (!out->f_op->splice_write)
306		return -EINVAL;
307
308	ret = file_remove_privs(iocb->ki_filp);
309	if (ret)
310		return ret;
311
312	scoped_with_creds(ctx->cred) {
313		file_start_write(out);
314		ret = out->f_op->splice_write(pipe, out, &iocb->ki_pos, len, flags);
315		file_end_write(out);
316	}
317
318	if (ctx->end_write)
319		ctx->end_write(iocb, ret);
320
321	return ret;
322}
323EXPORT_SYMBOL_GPL(backing_file_splice_write);
324
325int backing_file_mmap(struct file *file, struct vm_area_struct *vma,
326		      struct backing_file_ctx *ctx)
327{
328	struct file *user_file = vma->vm_file;
329	int ret;
330
331	if (WARN_ON_ONCE(!(file->f_mode & FMODE_BACKING)))
332		return -EIO;
333
334	if (!can_mmap_file(file))
335		return -ENODEV;
336
337	vma_set_file(vma, file);
338
339	scoped_with_creds(ctx->cred)
340		ret = vfs_mmap(vma->vm_file, vma);
341
342	if (ctx->accessed)
343		ctx->accessed(user_file);
344
345	return ret;
346}
347EXPORT_SYMBOL_GPL(backing_file_mmap);
348
349static int __init backing_aio_init(void)
350{
351	backing_aio_cachep = KMEM_CACHE(backing_aio, SLAB_HWCACHE_ALIGN);
352	if (!backing_aio_cachep)
353		return -ENOMEM;
354
355	return 0;
356}
357fs_initcall(backing_aio_init);