kernel/anon_inodes.c

   1 /*
   2  *  fs/anon_inodes.c
   3  *
   4  *  Copyright (C) 2007  Davide Libenzi <davidel@xmailserver.org>
   5  *
   6  *  Thanks to Arnd Bergmann for code review and suggestions.
   7  *  More changes for Thomas Gleixner suggestions.
   8  *
   9  */
  10
  11 #include <linux/file.h>
  12 #include <linux/poll.h>
  13 #include <linux/slab.h>
  14 #include <linux/init.h>
  15 #include <linux/fs.h>
  16 #include <linux/mount.h>
  17 #include <linux/module.h>
  18 #include <linux/kernel.h>
  19 #include <linux/magic.h>
  20 #include <linux/anon_inodes.h>
  21
  22 #include <asm/uaccess.h>
  23
  24 #if LINUX_VERSION_CODE < KERNEL_VERSION(2,6,23)
  25
  26 static struct vfsmount *anon_inode_mnt __read_mostly;
  27 static struct inode *anon_inode_inode;
  28 static struct file_operations anon_inode_fops;
  29
  30 #if LINUX_VERSION_CODE > KERNEL_VERSION(2,6,17)
  31
  32 static int anon_inodefs_get_sb(struct file_system_type *fs_type, int flags,
  33                                const char *dev_name, void *data,
  34                                struct vfsmount *mnt)
  35 {
  36         return get_sb_pseudo(fs_type, "kvm_anon_inode:", NULL, 0x99700426, mnt);
  37 }
  38
  39 #else
  40
  41 static struct super_block *anon_inodefs_get_sb(struct file_system_type *fs_type,
  42                                             int flags, const char *dev_name,
  43                                             void *data)
  44 {
  45         return get_sb_pseudo(fs_type, "kvm_anon_inode:", NULL, 0x99700426);
  46 }
  47
  48 #endif
  49
  50 static int anon_inodefs_delete_dentry(struct dentry *dentry)
  51 {
  52         /*
  53          * We faked vfs to believe the dentry was hashed when we created it.
  54          * Now we restore the flag so that dput() will work correctly.
  55          */
  56         dentry->d_flags |= DCACHE_UNHASHED;
  57         return 1;
  58 }
  59
  60 static struct file_system_type anon_inode_fs_type = {
  61         .name           = "kvm_anon_inodefs",
  62         .get_sb         = anon_inodefs_get_sb,
  63         .kill_sb        = kill_anon_super,
  64 };
  65 static struct dentry_operations anon_inodefs_dentry_operations = {
  66         .d_delete       = anon_inodefs_delete_dentry,
  67 };
  68
  69 /**
  70  * anon_inode_getfd - creates a new file instance by hooking it up to and
  71  *                    anonymous inode, and a dentry that describe the "class"
  72  *                    of the file
  73  *
  74  * @name:    [in]    name of the "class" of the new file
  75  * @fops     [in]    file operations for the new file
  76  * @priv     [in]    private data for the new file (will be file's private_data)
  77  *
  78  * Creates a new file by hooking it on a single inode. This is useful for files
  79  * that do not need to have a full-fledged inode in order to operate correctly.
  80  * All the files created with anon_inode_getfd() will share a single inode, by
  81  * hence saving memory and avoiding code duplication for the file/inode/dentry
  82  * setup. Returns new descriptor or -error.
  83  */
  84 int anon_inode_getfd(const char *name, const struct file_operations *fops,
  85                      void *priv, int flags)
  86 {
  87         struct qstr this;
  88         struct dentry *dentry;
  89         struct inode *inode;
  90         struct file *file;
  91         int error, fd;
  92
  93         if (IS_ERR(anon_inode_inode))
  94                 return -ENODEV;
  95         file = get_empty_filp();
  96         if (!file)
  97                 return -ENFILE;
  98
  99         inode = igrab(anon_inode_inode);
 100         if (IS_ERR(inode)) {
 101                 error = PTR_ERR(inode);
 102                 goto err_put_filp;
 103         }
 104
 105         error = get_unused_fd();
 106         if (error < 0)
 107                 goto err_iput;
 108         fd = error;
 109
 110         /*
 111          * Link the inode to a directory entry by creating a unique name
 112          * using the inode sequence number.
 113          */
 114         error = -ENOMEM;
 115         this.name = name;
 116         this.len = strlen(name);
 117         this.hash = 0;
 118         dentry = d_alloc(anon_inode_mnt->mnt_sb->s_root, &this);
 119         if (!dentry)
 120                 goto err_put_unused_fd;
 121         dentry->d_op = &anon_inodefs_dentry_operations;
 122         /* Do not publish this dentry inside the global dentry hash table */
 123         dentry->d_flags &= ~DCACHE_UNHASHED;
 124         d_instantiate(dentry, inode);
 125
 126         file->f_vfsmnt = mntget(anon_inode_mnt);
 127         file->f_dentry = dentry;
 128         file->f_mapping = inode->i_mapping;
 129
 130         file->f_pos = 0;
 131         file->f_flags = O_RDWR;
 132         file->f_op = (struct file_operations *)fops;
 133         file->f_mode = FMODE_READ | FMODE_WRITE;
 134         file->f_version = 0;
 135         file->private_data = priv;
 136
 137         fd_install(fd, file);
 138
 139         return fd;
 140
 141 err_put_unused_fd:
 142         put_unused_fd(fd);
 143 err_iput:
 144         iput(inode);
 145 err_put_filp:
 146         fput(file);
 147         return error;
 148 }
 149
 150 /*
 151  * A single inode exist for all anon_inode files. Contrary to pipes,
 152  * anon_inode inodes has no per-instance data associated, so we can avoid
 153  * the allocation of multiple of them.
 154  */
 155 static struct inode *anon_inode_mkinode(void)
 156 {
 157         struct inode *inode = new_inode(anon_inode_mnt->mnt_sb);
 158
 159         if (!inode)
 160                 return ERR_PTR(-ENOMEM);
 161
 162         inode->i_fop = &anon_inode_fops;
 163
 164         /*
 165          * Mark the inode dirty from the very beginning,
 166          * that way it will never be moved to the dirty
 167          * list because mark_inode_dirty() will think
 168          * that it already _is_ on the dirty list.
 169          */
 170         inode->i_state = I_DIRTY;
 171         inode->i_mode = S_IRUSR | S_IWUSR;
 172         inode->i_uid = current->fsuid;
 173         inode->i_gid = current->fsgid;
 174         inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
 175         return inode;
 176 }
 177
 178 static int anon_inode_init(void)
 179 {
 180         int error;
 181
 182         error = register_filesystem(&anon_inode_fs_type);
 183         if (error)
 184                 goto err_exit;
 185         anon_inode_mnt = kern_mount(&anon_inode_fs_type);
 186         if (IS_ERR(anon_inode_mnt)) {
 187                 error = PTR_ERR(anon_inode_mnt);
 188                 goto err_unregister_filesystem;
 189         }
 190         anon_inode_inode = anon_inode_mkinode();
 191         if (IS_ERR(anon_inode_inode)) {
 192                 error = PTR_ERR(anon_inode_inode);
 193                 goto err_mntput;
 194         }
 195
 196         return 0;
 197
 198 err_mntput:
 199         mntput(anon_inode_mnt);
 200 err_unregister_filesystem:
 201         unregister_filesystem(&anon_inode_fs_type);
 202 err_exit:
 203         return -ENOMEM;
 204 }
 205
 206 int kvm_init_anon_inodes(void)
 207 {
 208         return anon_inode_init();
 209 }
 210
 211 void kvm_exit_anon_inodes(void)
 212 {
 213         iput(anon_inode_inode);
 214         mntput(anon_inode_mnt);
 215         unregister_filesystem(&anon_inode_fs_type);
 216 }
 217
 218 #else
 219
 220 int kvm_init_anon_inodes(void)
 221 {
 222         return 0;
 223 }
 224
 225 void kvm_exit_anon_inodes(void)
 226 {
 227 }
 228
 229 #undef anon_inode_getfd
 230
 231 #if LINUX_VERSION_CODE < KERNEL_VERSION(2,6,26)
 232
 233 int kvm_anon_inode_getfd(const char *name,
 234                          const struct file_operations *fops,
 235                          void *priv, int flags)
 236 {
 237         int r;
 238         int fd;
 239         struct inode *inode;
 240         struct file *file;
 241
 242         r = anon_inode_getfd(&fd, &inode, &file, name, fops, priv);
 243         if (r < 0)
 244                 return r;
 245         return fd;
 246 }
 247
 248 #elif LINUX_VERSION_CODE == KERNEL_VERSION(2,6,26)
 249
 250 int kvm_anon_inode_getfd(const char *name,
 251                          const struct file_operations *fops,
 252                          void *priv, int flags)
 253 {
 254         return anon_inode_getfd(name, fops, priv);
 255 }
 256
 257 #else
 258
 259 int kvm_anon_inode_getfd(const char *name,
 260                          const struct file_operations *fops,
 261                          void *priv, int flags)
 262 {
 263         return anon_inode_getfd(name, fops, priv, flags);
 264 }
 265
 266 #endif
 267
 268 #endif