inode.c

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    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/module.h>
   27 #include <linux/fs.h>
   28 #include <linux/pagemap.h>
   29 #include <linux/init.h>
   30 #include <linux/string.h>
   31 #include <linux/locks.h>
   32 
   33 #include <asm/uaccess.h>
   34 
   35 /* some random number */
   36 #define RAMFS_MAGIC     0x858458f6
   37 
   38 static struct super_operations ramfs_ops;
   39 static struct address_space_operations ramfs_aops;
   40 static struct file_operations ramfs_file_operations;
   41 static struct inode_operations ramfs_dir_inode_operations;
   42 
   43 static int ramfs_statfs(struct super_block *sb, struct statfs *buf)
   44 {
   45         buf->f_type = RAMFS_MAGIC;
   46         buf->f_bsize = PAGE_CACHE_SIZE;
   47         buf->f_namelen = 255;
   48         return 0;
   49 }
   50 
   51 /*
   52  * Lookup the data. This is trivial - if the dentry didn't already
   53  * exist, we know it is negative.
   54  */
   55 static struct dentry * ramfs_lookup(struct inode *dir, struct dentry *dentry)
   56 {
   57         d_add(dentry, NULL);
   58         return NULL;
   59 }
   60 
   61 /*
   62  * Read a page. Again trivial. If it didn't already exist
   63  * in the page cache, it is zero-filled.
   64  */
   65 static int ramfs_readpage(struct file *file, struct page * page)
   66 {
   67         if (!Page_Uptodate(page)) {
   68                 memset(kmap(page), 0, PAGE_CACHE_SIZE);
   69                 kunmap(page);
   70                 flush_dcache_page(page);
   71                 SetPageUptodate(page);
   72         }
   73         UnlockPage(page);
   74         return 0;
   75 }
   76 
   77 static int ramfs_prepare_write(struct file *file, struct page *page, unsigned offset, unsigned to)
   78 {
   79         void *addr = kmap(page);
   80         if (!Page_Uptodate(page)) {
   81                 memset(addr, 0, PAGE_CACHE_SIZE);
   82                 flush_dcache_page(page);
   83                 SetPageUptodate(page);
   84         }
   85         SetPageDirty(page);
   86         return 0;
   87 }
   88 
   89 static int ramfs_commit_write(struct file *file, struct page *page, unsigned offset, unsigned to)
   90 {
   91         struct inode *inode = page->mapping->host;
   92         loff_t pos = ((loff_t)page->index << PAGE_CACHE_SHIFT) + to;
   93 
   94         kunmap(page);
   95         if (pos > inode->i_size)
   96                 inode->i_size = pos;
   97         return 0;
   98 }
   99 
  100 struct inode *ramfs_get_inode(struct super_block *sb, int mode, int dev)
  101 {
  102         struct inode * inode = new_inode(sb);
  103 
  104         if (inode) {
  105                 inode->i_mode = mode;
  106                 inode->i_uid = current->fsuid;
  107                 inode->i_gid = current->fsgid;
  108                 inode->i_blksize = PAGE_CACHE_SIZE;
  109                 inode->i_blocks = 0;
  110                 inode->i_rdev = NODEV;
  111                 inode->i_mapping->a_ops = &ramfs_aops;
  112                 inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
  113                 switch (mode & S_IFMT) {
  114                 default:
  115                         init_special_inode(inode, mode, dev);
  116                         break;
  117                 case S_IFREG:
  118                         inode->i_fop = &ramfs_file_operations;
  119                         break;
  120                 case S_IFDIR:
  121                         inode->i_op = &ramfs_dir_inode_operations;
  122                         inode->i_fop = &dcache_dir_ops;
  123                         break;
  124                 case S_IFLNK:
  125                         inode->i_op = &page_symlink_inode_operations;
  126                         break;
  127                 }
  128         }
  129         return inode;
  130 }
  131 
  132 /*
  133  * File creation. Allocate an inode, and we're done..
  134  */
  135 static int ramfs_mknod(struct inode *dir, struct dentry *dentry, int mode, int dev)
  136 {
  137         struct inode * inode = ramfs_get_inode(dir->i_sb, mode, dev);
  138         int error = -ENOSPC;
  139 
  140         if (inode) {
  141                 d_instantiate(dentry, inode);
  142                 dget(dentry);           /* Extra count - pin the dentry in core */
  143                 error = 0;
  144         }
  145         return error;
  146 }
  147 
  148 static int ramfs_mkdir(struct inode * dir, struct dentry * dentry, int mode)
  149 {
  150         return ramfs_mknod(dir, dentry, mode | S_IFDIR, 0);
  151 }
  152 
  153 static int ramfs_create(struct inode *dir, struct dentry *dentry, int mode)
  154 {
  155         return ramfs_mknod(dir, dentry, mode | S_IFREG, 0);
  156 }
  157 
  158 /*
  159  * Link a file..
  160  */
  161 static int ramfs_link(struct dentry *old_dentry, struct inode * dir, struct dentry * dentry)
  162 {
  163         struct inode *inode = old_dentry->d_inode;
  164 
  165         if (S_ISDIR(inode->i_mode))
  166                 return -EPERM;
  167 
  168         inode->i_nlink++;
  169         atomic_inc(&inode->i_count);    /* New dentry reference */
  170         dget(dentry);           /* Extra pinning count for the created dentry */
  171         d_instantiate(dentry, inode);
  172         return 0;
  173 }
  174 
  175 static inline int ramfs_positive(struct dentry *dentry)
  176 {
  177         return dentry->d_inode && !d_unhashed(dentry);
  178 }
  179 
  180 /*
  181  * Check that a directory is empty (this works
  182  * for regular files too, they'll just always be
  183  * considered empty..).
  184  *
  185  * Note that an empty directory can still have
  186  * children, they just all have to be negative..
  187  */
  188 static int ramfs_empty(struct dentry *dentry)
  189 {
  190         struct list_head *list;
  191 
  192         spin_lock(&dcache_lock);
  193         list = dentry->d_subdirs.next;
  194 
  195         while (list != &dentry->d_subdirs) {
  196                 struct dentry *de = list_entry(list, struct dentry, d_child);
  197 
  198                 if (ramfs_positive(de)) {
  199                         spin_unlock(&dcache_lock);
  200                         return 0;
  201                 }
  202                 list = list->next;
  203         }
  204         spin_unlock(&dcache_lock);
  205         return 1;
  206 }
  207 
  208 /*
  209  * This works for both directories and regular files.
  210  * (non-directories will always have empty subdirs)
  211  */
  212 static int ramfs_unlink(struct inode * dir, struct dentry *dentry)
  213 {
  214         int retval = -ENOTEMPTY;
  215 
  216         if (ramfs_empty(dentry)) {
  217                 struct inode *inode = dentry->d_inode;
  218 
  219                 inode->i_nlink--;
  220                 dput(dentry);                   /* Undo the count from "create" - this does all the work */
  221                 retval = 0;
  222         }
  223         return retval;
  224 }
  225 
  226 #define ramfs_rmdir ramfs_unlink
  227 
  228 /*
  229  * The VFS layer already does all the dentry stuff for rename,
  230  * we just have to decrement the usage count for the target if
  231  * it exists so that the VFS layer correctly free's it when it
  232  * gets overwritten.
  233  */
  234 static int ramfs_rename(struct inode * old_dir, struct dentry *old_dentry, struct inode * new_dir,struct dentry *new_dentry)
  235 {
  236         int error = -ENOTEMPTY;
  237 
  238         if (ramfs_empty(new_dentry)) {
  239                 struct inode *inode = new_dentry->d_inode;
  240                 if (inode) {
  241                         inode->i_nlink--;
  242                         dput(new_dentry);
  243                 }
  244                 error = 0;
  245         }
  246         return error;
  247 }
  248 
  249 static int ramfs_symlink(struct inode * dir, struct dentry *dentry, const char * symname)
  250 {
  251         int error;
  252 
  253         error = ramfs_mknod(dir, dentry, S_IFLNK | S_IRWXUGO, 0);
  254         if (!error) {
  255                 int l = strlen(symname)+1;
  256                 struct inode *inode = dentry->d_inode;
  257                 error = block_symlink(inode, symname, l);
  258         }
  259         return error;
  260 }
  261 
  262 static int ramfs_sync_file(struct file * file, struct dentry *dentry, int datasync)
  263 {
  264         return 0;
  265 }
  266 
  267 static struct address_space_operations ramfs_aops = {
  268         readpage:       ramfs_readpage,
  269         writepage:      fail_writepage,
  270         prepare_write:  ramfs_prepare_write,
  271         commit_write:   ramfs_commit_write
  272 };
  273 
  274 static struct file_operations ramfs_file_operations = {
  275         read:           generic_file_read,
  276         write:          generic_file_write,
  277         mmap:           generic_file_mmap,
  278         fsync:          ramfs_sync_file,
  279 };
  280 
  281 static struct inode_operations ramfs_dir_inode_operations = {
  282         create:         ramfs_create,
  283         lookup:         ramfs_lookup,
  284         link:           ramfs_link,
  285         unlink:         ramfs_unlink,
  286         symlink:        ramfs_symlink,
  287         mkdir:          ramfs_mkdir,
  288         rmdir:          ramfs_rmdir,
  289         mknod:          ramfs_mknod,
  290         rename:         ramfs_rename,
  291 };
  292 
  293 static struct super_operations ramfs_ops = {
  294         statfs:         ramfs_statfs,
  295         put_inode:      force_delete,
  296 };
  297 
  298 static struct super_block *ramfs_read_super(struct super_block * sb, void * data, int silent)
  299 {
  300         struct inode * inode;
  301         struct dentry * root;
  302 
  303         sb->s_blocksize = PAGE_CACHE_SIZE;
  304         sb->s_blocksize_bits = PAGE_CACHE_SHIFT;
  305         sb->s_magic = RAMFS_MAGIC;
  306         sb->s_op = &ramfs_ops;
  307         inode = ramfs_get_inode(sb, S_IFDIR | 0755, 0);
  308         if (!inode)
  309                 return NULL;
  310 
  311         root = d_alloc_root(inode);
  312         if (!root) {
  313                 iput(inode);
  314                 return NULL;
  315         }
  316         sb->s_root = root;
  317         return sb;
  318 }
  319 
  320 static DECLARE_FSTYPE(ramfs_fs_type, "ramfs", ramfs_read_super, FS_LITTER);
  321 static DECLARE_FSTYPE(rootfs_fs_type, "rootfs", ramfs_read_super, FS_NOMOUNT|FS_LITTER);
  322 
  323 static int __init init_ramfs_fs(void)
  324 {
  325         return register_filesystem(&ramfs_fs_type);
  326 }
  327 
  328 static void __exit exit_ramfs_fs(void)
  329 {
  330         unregister_filesystem(&ramfs_fs_type);
  331 }
  332 
  333 module_init(init_ramfs_fs)
  334 module_exit(exit_ramfs_fs)
  335 
  336 int __init init_rootfs(void)
  337 {
  338         return register_filesystem(&rootfs_fs_type);
  339 }
  340 
  341 MODULE_LICENSE("GPL");
  342
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FreeBSD/Linux Kernel Cross Reference sys/fs/ramfs/inode.c

FreeBSD/Linux Kernel Cross Reference
sys/fs/ramfs/inode.c
