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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 struct inode *ramfs_get_inode(struct super_block *sb,
 54                                 const struct inode *dir, umode_t mode, dev_t dev)
 55 {
 56         struct inode * inode = new_inode(sb);
 57 
 58         if (inode) {
 59                 inode->i_ino = get_next_ino();
 60                 inode_init_owner(inode, dir, mode);
 61                 inode->i_mapping->a_ops = &ramfs_aops;
 62                 mapping_set_gfp_mask(inode->i_mapping, GFP_HIGHUSER);
 63                 mapping_set_unevictable(inode->i_mapping);
 64                 inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
 65                 switch (mode & S_IFMT) {
 66                 default:
 67                         init_special_inode(inode, mode, dev);
 68                         break;
 69                 case S_IFREG:
 70                         inode->i_op = &ramfs_file_inode_operations;
 71                         inode->i_fop = &ramfs_file_operations;
 72                         break;
 73                 case S_IFDIR:
 74                         inode->i_op = &ramfs_dir_inode_operations;
 75                         inode->i_fop = &simple_dir_operations;
 76 
 77                         /* directory inodes start off with i_nlink == 2 (for "." entry) */
 78                         inc_nlink(inode);
 79                         break;
 80                 case S_IFLNK:
 81                         inode->i_op = &page_symlink_inode_operations;
 82                         break;
 83                 }
 84         }
 85         return inode;
 86 }
 87 
 88 /*
 89  * File creation. Allocate an inode, and we're done..
 90  */
 91 /* SMP-safe */
 92 static int
 93 ramfs_mknod(struct inode *dir, struct dentry *dentry, umode_t mode, dev_t dev)
 94 {
 95         struct inode * inode = ramfs_get_inode(dir->i_sb, dir, mode, dev);
 96         int error = -ENOSPC;
 97 
 98         if (inode) {
 99                 d_instantiate(dentry, inode);
100                 dget(dentry);   /* Extra count - pin the dentry in core */
101                 error = 0;
102                 dir->i_mtime = dir->i_ctime = CURRENT_TIME;
103         }
104         return error;
105 }
106 
107 static int ramfs_mkdir(struct inode * dir, struct dentry * dentry, umode_t mode)
108 {
109         int retval = ramfs_mknod(dir, dentry, mode | S_IFDIR, 0);
110         if (!retval)
111                 inc_nlink(dir);
112         return retval;
113 }
114 
115 static int ramfs_create(struct inode *dir, struct dentry *dentry, umode_t mode, bool excl)
116 {
117         return ramfs_mknod(dir, dentry, mode | S_IFREG, 0);
118 }
119 
120 static int ramfs_symlink(struct inode * dir, struct dentry *dentry, const char * symname)
121 {
122         struct inode *inode;
123         int error = -ENOSPC;
124 
125         inode = ramfs_get_inode(dir->i_sb, dir, S_IFLNK|S_IRWXUGO, 0);
126         if (inode) {
127                 int l = strlen(symname)+1;
128                 error = page_symlink(inode, symname, l);
129                 if (!error) {
130                         d_instantiate(dentry, inode);
131                         dget(dentry);
132                         dir->i_mtime = dir->i_ctime = CURRENT_TIME;
133                 } else
134                         iput(inode);
135         }
136         return error;
137 }
138 
139 static const struct inode_operations ramfs_dir_inode_operations = {
140         .create         = ramfs_create,
141         .lookup         = simple_lookup,
142         .link           = simple_link,
143         .unlink         = simple_unlink,
144         .symlink        = ramfs_symlink,
145         .mkdir          = ramfs_mkdir,
146         .rmdir          = simple_rmdir,
147         .mknod          = ramfs_mknod,
148         .rename         = simple_rename,
149 };
150 
151 static const struct super_operations ramfs_ops = {
152         .statfs         = simple_statfs,
153         .drop_inode     = generic_delete_inode,
154         .show_options   = generic_show_options,
155 };
156 
157 struct ramfs_mount_opts {
158         umode_t mode;
159 };
160 
161 enum {
162         Opt_mode,
163         Opt_err
164 };
165 
166 static const match_table_t tokens = {
167         {Opt_mode, "mode=%o"},
168         {Opt_err, NULL}
169 };
170 
171 struct ramfs_fs_info {
172         struct ramfs_mount_opts mount_opts;
173 };
174 
175 static int ramfs_parse_options(char *data, struct ramfs_mount_opts *opts)
176 {
177         substring_t args[MAX_OPT_ARGS];
178         int option;
179         int token;
180         char *p;
181 
182         opts->mode = RAMFS_DEFAULT_MODE;
183 
184         while ((p = strsep(&data, ",")) != NULL) {
185                 if (!*p)
186                         continue;
187 
188                 token = match_token(p, tokens, args);
189                 switch (token) {
190                 case Opt_mode:
191                         if (match_octal(&args[0], &option))
192                                 return -EINVAL;
193                         opts->mode = option & S_IALLUGO;
194                         break;
195                 /*
196                  * We might like to report bad mount options here;
197                  * but traditionally ramfs has ignored all mount options,
198                  * and as it is used as a !CONFIG_SHMEM simple substitute
199                  * for tmpfs, better continue to ignore other mount options.
200                  */
201                 }
202         }
203 
204         return 0;
205 }
206 
207 int ramfs_fill_super(struct super_block *sb, void *data, int silent)
208 {
209         struct ramfs_fs_info *fsi;
210         struct inode *inode;
211         int err;
212 
213         save_mount_options(sb, data);
214 
215         fsi = kzalloc(sizeof(struct ramfs_fs_info), GFP_KERNEL);
216         sb->s_fs_info = fsi;
217         if (!fsi)
218                 return -ENOMEM;
219 
220         err = ramfs_parse_options(data, &fsi->mount_opts);
221         if (err)
222                 return err;
223 
224         sb->s_maxbytes          = MAX_LFS_FILESIZE;
225         sb->s_blocksize         = PAGE_CACHE_SIZE;
226         sb->s_blocksize_bits    = PAGE_CACHE_SHIFT;
227         sb->s_magic             = RAMFS_MAGIC;
228         sb->s_op                = &ramfs_ops;
229         sb->s_time_gran         = 1;
230 
231         inode = ramfs_get_inode(sb, NULL, S_IFDIR | fsi->mount_opts.mode, 0);
232         sb->s_root = d_make_root(inode);
233         if (!sb->s_root)
234                 return -ENOMEM;
235 
236         return 0;
237 }
238 
239 struct dentry *ramfs_mount(struct file_system_type *fs_type,
240         int flags, const char *dev_name, void *data)
241 {
242         return mount_nodev(fs_type, flags, data, ramfs_fill_super);
243 }
244 
245 static void ramfs_kill_sb(struct super_block *sb)
246 {
247         kfree(sb->s_fs_info);
248         kill_litter_super(sb);
249 }
250 
251 static struct file_system_type ramfs_fs_type = {
252         .name           = "ramfs",
253         .mount          = ramfs_mount,
254         .kill_sb        = ramfs_kill_sb,
255         .fs_flags       = FS_USERNS_MOUNT,
256 };
257 
258 int __init init_ramfs_fs(void)
259 {
260         static unsigned long once;
261 
262         if (test_and_set_bit(0, &once))
263                 return 0;
264         return register_filesystem(&ramfs_fs_type);
265 }
266 fs_initcall(init_ramfs_fs);
267 

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