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Linux/fs/ramfs/inode.c

  1 /*
  2  * Resizable simple ram filesystem for Linux.
  3  *
  4  * Copyright (C) 2000 Linus Torvalds.
  5  *               2000 Transmeta Corp.
  6  *
  7  * Usage limits added by David Gibson, Linuxcare Australia.
  8  * This file is released under the GPL.
  9  */
 10 
 11 /*
 12  * NOTE! This filesystem is probably most useful
 13  * not as a real filesystem, but as an example of
 14  * how virtual filesystems can be written.
 15  *
 16  * It doesn't get much simpler than this. Consider
 17  * that this file implements the full semantics of
 18  * a POSIX-compliant read-write filesystem.
 19  *
 20  * Note in particular how the filesystem does not
 21  * need to implement any data structures of its own
 22  * to keep track of the virtual data: using the VFS
 23  * caches is sufficient.
 24  */
 25 
 26 #include <linux/fs.h>
 27 #include <linux/pagemap.h>
 28 #include <linux/highmem.h>
 29 #include <linux/time.h>
 30 #include <linux/init.h>
 31 #include <linux/string.h>
 32 #include <linux/backing-dev.h>
 33 #include <linux/ramfs.h>
 34 #include <linux/sched.h>
 35 #include <linux/parser.h>
 36 #include <linux/magic.h>
 37 #include <linux/slab.h>
 38 #include <asm/uaccess.h>
 39 #include "internal.h"
 40 
 41 #define RAMFS_DEFAULT_MODE      0755
 42 
 43 static const struct super_operations ramfs_ops;
 44 static const struct inode_operations ramfs_dir_inode_operations;
 45 
 46 static const struct address_space_operations ramfs_aops = {
 47         .readpage       = simple_readpage,
 48         .write_begin    = simple_write_begin,
 49         .write_end      = simple_write_end,
 50         .set_page_dirty = __set_page_dirty_no_writeback,
 51 };
 52 
 53 static struct backing_dev_info ramfs_backing_dev_info = {
 54         .name           = "ramfs",
 55         .ra_pages       = 0,    /* No readahead */
 56         .capabilities   = BDI_CAP_NO_ACCT_AND_WRITEBACK |
 57                           BDI_CAP_MAP_DIRECT | BDI_CAP_MAP_COPY |
 58                           BDI_CAP_READ_MAP | BDI_CAP_WRITE_MAP | BDI_CAP_EXEC_MAP,
 59 };
 60 
 61 struct inode *ramfs_get_inode(struct super_block *sb,
 62                                 const struct inode *dir, umode_t mode, dev_t dev)
 63 {
 64         struct inode * inode = new_inode(sb);
 65 
 66         if (inode) {
 67                 inode->i_ino = get_next_ino();
 68                 inode_init_owner(inode, dir, mode);
 69                 inode->i_mapping->a_ops = &ramfs_aops;
 70                 inode->i_mapping->backing_dev_info = &ramfs_backing_dev_info;
 71                 mapping_set_gfp_mask(inode->i_mapping, GFP_HIGHUSER);
 72                 mapping_set_unevictable(inode->i_mapping);
 73                 inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
 74                 switch (mode & S_IFMT) {
 75                 default:
 76                         init_special_inode(inode, mode, dev);
 77                         break;
 78                 case S_IFREG:
 79                         inode->i_op = &ramfs_file_inode_operations;
 80                         inode->i_fop = &ramfs_file_operations;
 81                         break;
 82                 case S_IFDIR:
 83                         inode->i_op = &ramfs_dir_inode_operations;
 84                         inode->i_fop = &simple_dir_operations;
 85 
 86                         /* directory inodes start off with i_nlink == 2 (for "." entry) */
 87                         inc_nlink(inode);
 88                         break;
 89                 case S_IFLNK:
 90                         inode->i_op = &page_symlink_inode_operations;
 91                         break;
 92                 }
 93         }
 94         return inode;
 95 }
 96 
 97 /*
 98  * File creation. Allocate an inode, and we're done..
 99  */
100 /* SMP-safe */
101 static int
102 ramfs_mknod(struct inode *dir, struct dentry *dentry, umode_t mode, dev_t dev)
103 {
104         struct inode * inode = ramfs_get_inode(dir->i_sb, dir, mode, dev);
105         int error = -ENOSPC;
106 
107         if (inode) {
108                 d_instantiate(dentry, inode);
109                 dget(dentry);   /* Extra count - pin the dentry in core */
110                 error = 0;
111                 dir->i_mtime = dir->i_ctime = CURRENT_TIME;
112         }
113         return error;
114 }
115 
116 static int ramfs_mkdir(struct inode * dir, struct dentry * dentry, umode_t mode)
117 {
118         int retval = ramfs_mknod(dir, dentry, mode | S_IFDIR, 0);
119         if (!retval)
120                 inc_nlink(dir);
121         return retval;
122 }
123 
124 static int ramfs_create(struct inode *dir, struct dentry *dentry, umode_t mode, bool excl)
125 {
126         return ramfs_mknod(dir, dentry, mode | S_IFREG, 0);
127 }
128 
129 static int ramfs_symlink(struct inode * dir, struct dentry *dentry, const char * symname)
130 {
131         struct inode *inode;
132         int error = -ENOSPC;
133 
134         inode = ramfs_get_inode(dir->i_sb, dir, S_IFLNK|S_IRWXUGO, 0);
135         if (inode) {
136                 int l = strlen(symname)+1;
137                 error = page_symlink(inode, symname, l);
138                 if (!error) {
139                         d_instantiate(dentry, inode);
140                         dget(dentry);
141                         dir->i_mtime = dir->i_ctime = CURRENT_TIME;
142                 } else
143                         iput(inode);
144         }
145         return error;
146 }
147 
148 static const struct inode_operations ramfs_dir_inode_operations = {
149         .create         = ramfs_create,
150         .lookup         = simple_lookup,
151         .link           = simple_link,
152         .unlink         = simple_unlink,
153         .symlink        = ramfs_symlink,
154         .mkdir          = ramfs_mkdir,
155         .rmdir          = simple_rmdir,
156         .mknod          = ramfs_mknod,
157         .rename         = simple_rename,
158 };
159 
160 static const struct super_operations ramfs_ops = {
161         .statfs         = simple_statfs,
162         .drop_inode     = generic_delete_inode,
163         .show_options   = generic_show_options,
164 };
165 
166 struct ramfs_mount_opts {
167         umode_t mode;
168 };
169 
170 enum {
171         Opt_mode,
172         Opt_err
173 };
174 
175 static const match_table_t tokens = {
176         {Opt_mode, "mode=%o"},
177         {Opt_err, NULL}
178 };
179 
180 struct ramfs_fs_info {
181         struct ramfs_mount_opts mount_opts;
182 };
183 
184 static int ramfs_parse_options(char *data, struct ramfs_mount_opts *opts)
185 {
186         substring_t args[MAX_OPT_ARGS];
187         int option;
188         int token;
189         char *p;
190 
191         opts->mode = RAMFS_DEFAULT_MODE;
192 
193         while ((p = strsep(&data, ",")) != NULL) {
194                 if (!*p)
195                         continue;
196 
197                 token = match_token(p, tokens, args);
198                 switch (token) {
199                 case Opt_mode:
200                         if (match_octal(&args[0], &option))
201                                 return -EINVAL;
202                         opts->mode = option & S_IALLUGO;
203                         break;
204                 /*
205                  * We might like to report bad mount options here;
206                  * but traditionally ramfs has ignored all mount options,
207                  * and as it is used as a !CONFIG_SHMEM simple substitute
208                  * for tmpfs, better continue to ignore other mount options.
209                  */
210                 }
211         }
212 
213         return 0;
214 }
215 
216 int ramfs_fill_super(struct super_block *sb, void *data, int silent)
217 {
218         struct ramfs_fs_info *fsi;
219         struct inode *inode;
220         int err;
221 
222         save_mount_options(sb, data);
223 
224         fsi = kzalloc(sizeof(struct ramfs_fs_info), GFP_KERNEL);
225         sb->s_fs_info = fsi;
226         if (!fsi)
227                 return -ENOMEM;
228 
229         err = ramfs_parse_options(data, &fsi->mount_opts);
230         if (err)
231                 return err;
232 
233         sb->s_maxbytes          = MAX_LFS_FILESIZE;
234         sb->s_blocksize         = PAGE_CACHE_SIZE;
235         sb->s_blocksize_bits    = PAGE_CACHE_SHIFT;
236         sb->s_magic             = RAMFS_MAGIC;
237         sb->s_op                = &ramfs_ops;
238         sb->s_time_gran         = 1;
239 
240         inode = ramfs_get_inode(sb, NULL, S_IFDIR | fsi->mount_opts.mode, 0);
241         sb->s_root = d_make_root(inode);
242         if (!sb->s_root)
243                 return -ENOMEM;
244 
245         return 0;
246 }
247 
248 struct dentry *ramfs_mount(struct file_system_type *fs_type,
249         int flags, const char *dev_name, void *data)
250 {
251         return mount_nodev(fs_type, flags, data, ramfs_fill_super);
252 }
253 
254 static void ramfs_kill_sb(struct super_block *sb)
255 {
256         kfree(sb->s_fs_info);
257         kill_litter_super(sb);
258 }
259 
260 static struct file_system_type ramfs_fs_type = {
261         .name           = "ramfs",
262         .mount          = ramfs_mount,
263         .kill_sb        = ramfs_kill_sb,
264         .fs_flags       = FS_USERNS_MOUNT,
265 };
266 
267 int __init init_ramfs_fs(void)
268 {
269         static unsigned long once;
270         int err;
271 
272         if (test_and_set_bit(0, &once))
273                 return 0;
274 
275         err = bdi_init(&ramfs_backing_dev_info);
276         if (err)
277                 return err;
278 
279         err = register_filesystem(&ramfs_fs_type);
280         if (err)
281                 bdi_destroy(&ramfs_backing_dev_info);
282 
283         return err;
284 }
285 fs_initcall(init_ramfs_fs);
286 

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