xref: /openbmc/linux/fs/file_table.c (revision d5cb9783536a41df9f9cba5b0a1d78047ed787f7)
1 /*
2  *  linux/fs/file_table.c
3  *
4  *  Copyright (C) 1991, 1992  Linus Torvalds
5  *  Copyright (C) 1997 David S. Miller (davem@caip.rutgers.edu)
6  */
7 
8 #include <linux/string.h>
9 #include <linux/slab.h>
10 #include <linux/file.h>
11 #include <linux/init.h>
12 #include <linux/module.h>
13 #include <linux/smp_lock.h>
14 #include <linux/fs.h>
15 #include <linux/security.h>
16 #include <linux/eventpoll.h>
17 #include <linux/rcupdate.h>
18 #include <linux/mount.h>
19 #include <linux/cdev.h>
20 #include <linux/fsnotify.h>
21 
22 /* sysctl tunables... */
23 struct files_stat_struct files_stat = {
24 	.max_files = NR_FILE
25 };
26 
27 EXPORT_SYMBOL(files_stat); /* Needed by unix.o */
28 
29 /* public. Not pretty! */
30  __cacheline_aligned_in_smp DEFINE_SPINLOCK(files_lock);
31 
32 static DEFINE_SPINLOCK(filp_count_lock);
33 
34 /* slab constructors and destructors are called from arbitrary
35  * context and must be fully threaded - use a local spinlock
36  * to protect files_stat.nr_files
37  */
38 void filp_ctor(void *objp, struct kmem_cache *cachep, unsigned long cflags)
39 {
40 	if ((cflags & (SLAB_CTOR_VERIFY|SLAB_CTOR_CONSTRUCTOR)) ==
41 	    SLAB_CTOR_CONSTRUCTOR) {
42 		unsigned long flags;
43 		spin_lock_irqsave(&filp_count_lock, flags);
44 		files_stat.nr_files++;
45 		spin_unlock_irqrestore(&filp_count_lock, flags);
46 	}
47 }
48 
49 void filp_dtor(void *objp, struct kmem_cache *cachep, unsigned long dflags)
50 {
51 	unsigned long flags;
52 	spin_lock_irqsave(&filp_count_lock, flags);
53 	files_stat.nr_files--;
54 	spin_unlock_irqrestore(&filp_count_lock, flags);
55 }
56 
57 static inline void file_free_rcu(struct rcu_head *head)
58 {
59 	struct file *f =  container_of(head, struct file, f_u.fu_rcuhead);
60 	kmem_cache_free(filp_cachep, f);
61 }
62 
63 static inline void file_free(struct file *f)
64 {
65 	call_rcu(&f->f_u.fu_rcuhead, file_free_rcu);
66 }
67 
68 /* Find an unused file structure and return a pointer to it.
69  * Returns NULL, if there are no more free file structures or
70  * we run out of memory.
71  */
72 struct file *get_empty_filp(void)
73 {
74 	static int old_max;
75 	struct file * f;
76 
77 	/*
78 	 * Privileged users can go above max_files
79 	 */
80 	if (files_stat.nr_files >= files_stat.max_files &&
81 				!capable(CAP_SYS_ADMIN))
82 		goto over;
83 
84 	f = kmem_cache_alloc(filp_cachep, GFP_KERNEL);
85 	if (f == NULL)
86 		goto fail;
87 
88 	memset(f, 0, sizeof(*f));
89 	if (security_file_alloc(f))
90 		goto fail_sec;
91 
92 	eventpoll_init_file(f);
93 	atomic_set(&f->f_count, 1);
94 	f->f_uid = current->fsuid;
95 	f->f_gid = current->fsgid;
96 	rwlock_init(&f->f_owner.lock);
97 	/* f->f_version: 0 */
98 	INIT_LIST_HEAD(&f->f_u.fu_list);
99 	return f;
100 
101 over:
102 	/* Ran out of filps - report that */
103 	if (files_stat.nr_files > old_max) {
104 		printk(KERN_INFO "VFS: file-max limit %d reached\n",
105 					files_stat.max_files);
106 		old_max = files_stat.nr_files;
107 	}
108 	goto fail;
109 
110 fail_sec:
111 	file_free(f);
112 fail:
113 	return NULL;
114 }
115 
116 EXPORT_SYMBOL(get_empty_filp);
117 
118 void fastcall fput(struct file *file)
119 {
120 	if (rcuref_dec_and_test(&file->f_count))
121 		__fput(file);
122 }
123 
124 EXPORT_SYMBOL(fput);
125 
126 /* __fput is called from task context when aio completion releases the last
127  * last use of a struct file *.  Do not use otherwise.
128  */
129 void fastcall __fput(struct file *file)
130 {
131 	struct dentry *dentry = file->f_dentry;
132 	struct vfsmount *mnt = file->f_vfsmnt;
133 	struct inode *inode = dentry->d_inode;
134 
135 	might_sleep();
136 
137 	fsnotify_close(file);
138 	/*
139 	 * The function eventpoll_release() should be the first called
140 	 * in the file cleanup chain.
141 	 */
142 	eventpoll_release(file);
143 	locks_remove_flock(file);
144 
145 	if (file->f_op && file->f_op->release)
146 		file->f_op->release(inode, file);
147 	security_file_free(file);
148 	if (unlikely(inode->i_cdev != NULL))
149 		cdev_put(inode->i_cdev);
150 	fops_put(file->f_op);
151 	if (file->f_mode & FMODE_WRITE)
152 		put_write_access(inode);
153 	file_kill(file);
154 	file->f_dentry = NULL;
155 	file->f_vfsmnt = NULL;
156 	file_free(file);
157 	dput(dentry);
158 	mntput(mnt);
159 }
160 
161 struct file fastcall *fget(unsigned int fd)
162 {
163 	struct file *file;
164 	struct files_struct *files = current->files;
165 
166 	rcu_read_lock();
167 	file = fcheck_files(files, fd);
168 	if (file) {
169 		if (!rcuref_inc_lf(&file->f_count)) {
170 			/* File object ref couldn't be taken */
171 			rcu_read_unlock();
172 			return NULL;
173 		}
174 	}
175 	rcu_read_unlock();
176 
177 	return file;
178 }
179 
180 EXPORT_SYMBOL(fget);
181 
182 /*
183  * Lightweight file lookup - no refcnt increment if fd table isn't shared.
184  * You can use this only if it is guranteed that the current task already
185  * holds a refcnt to that file. That check has to be done at fget() only
186  * and a flag is returned to be passed to the corresponding fput_light().
187  * There must not be a cloning between an fget_light/fput_light pair.
188  */
189 struct file fastcall *fget_light(unsigned int fd, int *fput_needed)
190 {
191 	struct file *file;
192 	struct files_struct *files = current->files;
193 
194 	*fput_needed = 0;
195 	if (likely((atomic_read(&files->count) == 1))) {
196 		file = fcheck_files(files, fd);
197 	} else {
198 		rcu_read_lock();
199 		file = fcheck_files(files, fd);
200 		if (file) {
201 			if (rcuref_inc_lf(&file->f_count))
202 				*fput_needed = 1;
203 			else
204 				/* Didn't get the reference, someone's freed */
205 				file = NULL;
206 		}
207 		rcu_read_unlock();
208 	}
209 
210 	return file;
211 }
212 
213 
214 void put_filp(struct file *file)
215 {
216 	if (rcuref_dec_and_test(&file->f_count)) {
217 		security_file_free(file);
218 		file_kill(file);
219 		file_free(file);
220 	}
221 }
222 
223 void file_move(struct file *file, struct list_head *list)
224 {
225 	if (!list)
226 		return;
227 	file_list_lock();
228 	list_move(&file->f_u.fu_list, list);
229 	file_list_unlock();
230 }
231 
232 void file_kill(struct file *file)
233 {
234 	if (!list_empty(&file->f_u.fu_list)) {
235 		file_list_lock();
236 		list_del_init(&file->f_u.fu_list);
237 		file_list_unlock();
238 	}
239 }
240 
241 int fs_may_remount_ro(struct super_block *sb)
242 {
243 	struct list_head *p;
244 
245 	/* Check that no files are currently opened for writing. */
246 	file_list_lock();
247 	list_for_each(p, &sb->s_files) {
248 		struct file *file = list_entry(p, struct file, f_u.fu_list);
249 		struct inode *inode = file->f_dentry->d_inode;
250 
251 		/* File with pending delete? */
252 		if (inode->i_nlink == 0)
253 			goto too_bad;
254 
255 		/* Writeable file? */
256 		if (S_ISREG(inode->i_mode) && (file->f_mode & FMODE_WRITE))
257 			goto too_bad;
258 	}
259 	file_list_unlock();
260 	return 1; /* Tis' cool bro. */
261 too_bad:
262 	file_list_unlock();
263 	return 0;
264 }
265 
266 void __init files_init(unsigned long mempages)
267 {
268 	int n;
269 	/* One file with associated inode and dcache is very roughly 1K.
270 	 * Per default don't use more than 10% of our memory for files.
271 	 */
272 
273 	n = (mempages * (PAGE_SIZE / 1024)) / 10;
274 	files_stat.max_files = n;
275 	if (files_stat.max_files < NR_FILE)
276 		files_stat.max_files = NR_FILE;
277 	files_defer_init();
278 }
279