1 // SPDX-License-Identifier: GPL-2.0-only
3 * Common helpers for stackable filesystems and backing files.
5 * Forked from fs/overlayfs/file.c.
7 * Copyright (C) 2017 Red Hat, Inc.
8 * Copyright (C) 2023 CTERA Networks.
12 #include <linux/backing-file.h>
13 #include <linux/splice.h>
19 * backing_file_open - open a backing file for kernel internal use
20 * @user_path: path that the user reuqested to open
22 * @real_path: path of the backing file
23 * @cred: credentials for open
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().
32 struct file *backing_file_open(const struct path *user_path, int flags,
33 const struct path *real_path,
34 const struct cred *cred)
39 f = alloc_empty_backing_file(flags, cred);
44 *backing_file_user_path(f) = *user_path;
45 error = vfs_open(real_path, f);
53 EXPORT_SYMBOL_GPL(backing_file_open);
58 struct kiocb *orig_iocb;
59 /* used for aio completion */
60 void (*end_write)(struct file *);
61 struct work_struct work;
65 static struct kmem_cache *backing_aio_cachep;
67 #define BACKING_IOCB_MASK \
68 (IOCB_NOWAIT | IOCB_HIPRI | IOCB_DSYNC | IOCB_SYNC | IOCB_APPEND)
70 static rwf_t iocb_to_rw_flags(int flags)
72 return (__force rwf_t)(flags & BACKING_IOCB_MASK);
75 static void backing_aio_put(struct backing_aio *aio)
77 if (refcount_dec_and_test(&aio->ref)) {
78 fput(aio->iocb.ki_filp);
79 kmem_cache_free(backing_aio_cachep, aio);
83 static void backing_aio_cleanup(struct backing_aio *aio, long res)
85 struct kiocb *iocb = &aio->iocb;
86 struct kiocb *orig_iocb = aio->orig_iocb;
89 aio->end_write(orig_iocb->ki_filp);
91 orig_iocb->ki_pos = iocb->ki_pos;
95 static void backing_aio_rw_complete(struct kiocb *iocb, long res)
97 struct backing_aio *aio = container_of(iocb, struct backing_aio, iocb);
98 struct kiocb *orig_iocb = aio->orig_iocb;
100 if (iocb->ki_flags & IOCB_WRITE)
101 kiocb_end_write(iocb);
103 backing_aio_cleanup(aio, res);
104 orig_iocb->ki_complete(orig_iocb, res);
107 static void backing_aio_complete_work(struct work_struct *work)
109 struct backing_aio *aio = container_of(work, struct backing_aio, work);
111 backing_aio_rw_complete(&aio->iocb, aio->res);
114 static void backing_aio_queue_completion(struct kiocb *iocb, long res)
116 struct backing_aio *aio = container_of(iocb, struct backing_aio, iocb);
119 * Punt to a work queue to serialize updates of mtime/size.
122 INIT_WORK(&aio->work, backing_aio_complete_work);
123 queue_work(file_inode(aio->orig_iocb->ki_filp)->i_sb->s_dio_done_wq,
127 static int backing_aio_init_wq(struct kiocb *iocb)
129 struct super_block *sb = file_inode(iocb->ki_filp)->i_sb;
131 if (sb->s_dio_done_wq)
134 return sb_init_dio_done_wq(sb);
138 ssize_t backing_file_read_iter(struct file *file, struct iov_iter *iter,
139 struct kiocb *iocb, int flags,
140 struct backing_file_ctx *ctx)
142 struct backing_aio *aio = NULL;
143 const struct cred *old_cred;
146 if (WARN_ON_ONCE(!(file->f_mode & FMODE_BACKING)))
149 if (!iov_iter_count(iter))
152 if (iocb->ki_flags & IOCB_DIRECT &&
153 !(file->f_mode & FMODE_CAN_ODIRECT))
156 old_cred = override_creds(ctx->cred);
157 if (is_sync_kiocb(iocb)) {
158 rwf_t rwf = iocb_to_rw_flags(flags);
160 ret = vfs_iter_read(file, iter, &iocb->ki_pos, rwf);
163 aio = kmem_cache_zalloc(backing_aio_cachep, GFP_KERNEL);
167 aio->orig_iocb = iocb;
168 kiocb_clone(&aio->iocb, iocb, get_file(file));
169 aio->iocb.ki_complete = backing_aio_rw_complete;
170 refcount_set(&aio->ref, 2);
171 ret = vfs_iocb_iter_read(file, &aio->iocb, iter);
172 backing_aio_put(aio);
173 if (ret != -EIOCBQUEUED)
174 backing_aio_cleanup(aio, ret);
177 revert_creds(old_cred);
180 ctx->accessed(ctx->user_file);
184 EXPORT_SYMBOL_GPL(backing_file_read_iter);
186 ssize_t backing_file_write_iter(struct file *file, struct iov_iter *iter,
187 struct kiocb *iocb, int flags,
188 struct backing_file_ctx *ctx)
190 const struct cred *old_cred;
193 if (WARN_ON_ONCE(!(file->f_mode & FMODE_BACKING)))
196 if (!iov_iter_count(iter))
199 ret = file_remove_privs(ctx->user_file);
203 if (iocb->ki_flags & IOCB_DIRECT &&
204 !(file->f_mode & FMODE_CAN_ODIRECT))
208 * Stacked filesystems don't support deferred completions, don't copy
209 * this property in case it is set by the issuer.
211 flags &= ~IOCB_DIO_CALLER_COMP;
213 old_cred = override_creds(ctx->cred);
214 if (is_sync_kiocb(iocb)) {
215 rwf_t rwf = iocb_to_rw_flags(flags);
217 ret = vfs_iter_write(file, iter, &iocb->ki_pos, rwf);
219 ctx->end_write(ctx->user_file);
221 struct backing_aio *aio;
223 ret = backing_aio_init_wq(iocb);
228 aio = kmem_cache_zalloc(backing_aio_cachep, GFP_KERNEL);
232 aio->orig_iocb = iocb;
233 aio->end_write = ctx->end_write;
234 kiocb_clone(&aio->iocb, iocb, get_file(file));
235 aio->iocb.ki_flags = flags;
236 aio->iocb.ki_complete = backing_aio_queue_completion;
237 refcount_set(&aio->ref, 2);
238 ret = vfs_iocb_iter_write(file, &aio->iocb, iter);
239 backing_aio_put(aio);
240 if (ret != -EIOCBQUEUED)
241 backing_aio_cleanup(aio, ret);
244 revert_creds(old_cred);
248 EXPORT_SYMBOL_GPL(backing_file_write_iter);
250 ssize_t backing_file_splice_read(struct file *in, loff_t *ppos,
251 struct pipe_inode_info *pipe, size_t len,
253 struct backing_file_ctx *ctx)
255 const struct cred *old_cred;
258 if (WARN_ON_ONCE(!(in->f_mode & FMODE_BACKING)))
261 old_cred = override_creds(ctx->cred);
262 ret = vfs_splice_read(in, ppos, pipe, len, flags);
263 revert_creds(old_cred);
266 ctx->accessed(ctx->user_file);
270 EXPORT_SYMBOL_GPL(backing_file_splice_read);
272 ssize_t backing_file_splice_write(struct pipe_inode_info *pipe,
273 struct file *out, loff_t *ppos, size_t len,
275 struct backing_file_ctx *ctx)
277 const struct cred *old_cred;
280 if (WARN_ON_ONCE(!(out->f_mode & FMODE_BACKING)))
283 ret = file_remove_privs(ctx->user_file);
287 old_cred = override_creds(ctx->cred);
288 file_start_write(out);
289 ret = iter_file_splice_write(pipe, out, ppos, len, flags);
291 revert_creds(old_cred);
294 ctx->end_write(ctx->user_file);
298 EXPORT_SYMBOL_GPL(backing_file_splice_write);
300 int backing_file_mmap(struct file *file, struct vm_area_struct *vma,
301 struct backing_file_ctx *ctx)
303 const struct cred *old_cred;
306 if (WARN_ON_ONCE(!(file->f_mode & FMODE_BACKING)) ||
307 WARN_ON_ONCE(ctx->user_file != vma->vm_file))
310 if (!file->f_op->mmap)
313 vma_set_file(vma, file);
315 old_cred = override_creds(ctx->cred);
316 ret = call_mmap(vma->vm_file, vma);
317 revert_creds(old_cred);
320 ctx->accessed(ctx->user_file);
324 EXPORT_SYMBOL_GPL(backing_file_mmap);
326 static int __init backing_aio_init(void)
328 backing_aio_cachep = KMEM_CACHE(backing_aio, SLAB_HWCACHE_ALIGN);
329 if (!backing_aio_cachep)
334 fs_initcall(backing_aio_init);