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 /* anon_inodes on RHEL >= 5.2 is equivalent to 2.6.27 version */
  25 #ifdef RHEL_RELEASE_CODE
  26 #  if (RHEL_RELEASE_CODE >= RHEL_RELEASE_VERSION(5,2)) && defined(CONFIG_ANON_INODES)
  27 #    define RHEL_ANON_INODES
  28 #  endif
  29 #endif
  30
  31 #if LINUX_VERSION_CODE < KERNEL_VERSION(2,6,23) && !defined(RHEL_ANON_INODES)
  32
  33 static struct vfsmount *anon_inode_mnt __read_mostly;
  34 static struct inode *anon_inode_inode;
  35 static struct file_operations anon_inode_fops;
  36
  37 #if LINUX_VERSION_CODE > KERNEL_VERSION(2,6,17)
  38
  39 static int anon_inodefs_get_sb(struct file_system_type *fs_type, int flags,
  40                                const char *dev_name, void *data,
  41                                struct vfsmount *mnt)
  42 {
  43         return get_sb_pseudo(fs_type, "kvm_anon_inode:", NULL, 0x99700426, mnt);
  44 }
  45
  46 #else
  47
  48 static struct super_block *anon_inodefs_get_sb(struct file_system_type *fs_type,
  49                                             int flags, const char *dev_name,
  50                                             void *data)
  51 {
  52         return get_sb_pseudo(fs_type, "kvm_anon_inode:", NULL, 0x99700426);
  53 }
  54
  55 #endif
  56
  57 static int anon_inodefs_delete_dentry(struct dentry *dentry)
  58 {
  59         /*
  60          * We faked vfs to believe the dentry was hashed when we created it.
  61          * Now we restore the flag so that dput() will work correctly.
  62          */
  63         dentry->d_flags |= DCACHE_UNHASHED;
  64         return 1;
  65 }
  66
  67 static struct file_system_type anon_inode_fs_type = {
  68         .name           = "kvm_anon_inodefs",
  69         .get_sb         = anon_inodefs_get_sb,
  70         .kill_sb        = kill_anon_super,
  71 };
  72 static struct dentry_operations anon_inodefs_dentry_operations = {
  73         .d_delete       = anon_inodefs_delete_dentry,
  74 };
  75
  76 /**
  77  * anon_inode_getfd - creates a new file instance by hooking it up to and
  78  *                    anonymous inode, and a dentry that describe the "class"
  79  *                    of the file
  80  *
  81  * @name:    [in]    name of the "class" of the new file
  82  * @fops     [in]    file operations for the new file
  83  * @priv     [in]    private data for the new file (will be file's private_data)
  84  *
  85  * Creates a new file by hooking it on a single inode. This is useful for files
  86  * that do not need to have a full-fledged inode in order to operate correctly.
  87  * All the files created with anon_inode_getfd() will share a single inode, by
  88  * hence saving memory and avoiding code duplication for the file/inode/dentry
  89  * setup. Returns new descriptor or -error.
  90  */
  91 int anon_inode_getfd(const char *name, const struct file_operations *fops,
  92                      void *priv, int flags)
  93 {
  94         struct qstr this;
  95         struct dentry *dentry;
  96         struct inode *inode;
  97         struct file *file;
  98         int error, fd;
  99
 100         if (IS_ERR(anon_inode_inode))
 101                 return -ENODEV;
 102         file = get_empty_filp();
 103         if (!file)
 104                 return -ENFILE;
 105
 106         inode = igrab(anon_inode_inode);
 107         if (IS_ERR(inode)) {
 108                 error = PTR_ERR(inode);
 109                 goto err_put_filp;
 110         }
 111
 112         error = get_unused_fd();
 113         if (error < 0)
 114                 goto err_iput;
 115         fd = error;
 116
 117         /*
 118          * Link the inode to a directory entry by creating a unique name
 119          * using the inode sequence number.
 120          */
 121         error = -ENOMEM;
 122         this.name = name;
 123         this.len = strlen(name);
 124         this.hash = 0;
 125         dentry = d_alloc(anon_inode_mnt->mnt_sb->s_root, &this);
 126         if (!dentry)
 127                 goto err_put_unused_fd;
 128         dentry->d_op = &anon_inodefs_dentry_operations;
 129         /* Do not publish this dentry inside the global dentry hash table */
 130         dentry->d_flags &= ~DCACHE_UNHASHED;
 131         d_instantiate(dentry, inode);
 132
 133         file->f_vfsmnt = mntget(anon_inode_mnt);
 134         file->f_dentry = dentry;
 135         file->f_mapping = inode->i_mapping;
 136
 137         file->f_pos = 0;
 138         file->f_flags = O_RDWR;
 139         file->f_op = (struct file_operations *)fops;
 140         file->f_mode = FMODE_READ | FMODE_WRITE;
 141         file->f_version = 0;
 142         file->private_data = priv;
 143
 144         fd_install(fd, file);
 145
 146         return fd;
 147
 148 err_put_unused_fd:
 149         put_unused_fd(fd);
 150 err_iput:
 151         iput(inode);
 152 err_put_filp:
 153         fput(file);
 154         return error;
 155 }
 156
 157 /*
 158  * A single inode exist for all anon_inode files. Contrary to pipes,
 159  * anon_inode inodes has no per-instance data associated, so we can avoid
 160  * the allocation of multiple of them.
 161  */
 162 static struct inode *anon_inode_mkinode(void)
 163 {
 164         struct inode *inode = new_inode(anon_inode_mnt->mnt_sb);
 165
 166         if (!inode)
 167                 return ERR_PTR(-ENOMEM);
 168
 169         inode->i_fop = &anon_inode_fops;
 170
 171         /*
 172          * Mark the inode dirty from the very beginning,
 173          * that way it will never be moved to the dirty
 174          * list because mark_inode_dirty() will think
 175          * that it already _is_ on the dirty list.
 176          */
 177         inode->i_state = I_DIRTY;
 178         inode->i_mode = S_IRUSR | S_IWUSR;
 179         inode->i_uid = current->fsuid;
 180         inode->i_gid = current->fsgid;
 181         inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
 182         return inode;
 183 }
 184
 185 static int anon_inode_init(void)
 186 {
 187         int error;
 188
 189         error = register_filesystem(&anon_inode_fs_type);
 190         if (error)
 191                 goto err_exit;
 192         anon_inode_mnt = kern_mount(&anon_inode_fs_type);
 193         if (IS_ERR(anon_inode_mnt)) {
 194                 error = PTR_ERR(anon_inode_mnt);
 195                 goto err_unregister_filesystem;
 196         }
 197         anon_inode_inode = anon_inode_mkinode();
 198         if (IS_ERR(anon_inode_inode)) {
 199                 error = PTR_ERR(anon_inode_inode);
 200                 goto err_mntput;
 201         }
 202
 203         return 0;
 204
 205 err_mntput:
 206         mntput(anon_inode_mnt);
 207 err_unregister_filesystem:
 208         unregister_filesystem(&anon_inode_fs_type);
 209 err_exit:
 210         return -ENOMEM;
 211 }
 212
 213 int kvm_init_anon_inodes(void)
 214 {
 215         return anon_inode_init();
 216 }
 217
 218 void kvm_exit_anon_inodes(void)
 219 {
 220         iput(anon_inode_inode);
 221         mntput(anon_inode_mnt);
 222         unregister_filesystem(&anon_inode_fs_type);
 223 }
 224
 225 #else
 226
 227 int kvm_init_anon_inodes(void)
 228 {
 229         return 0;
 230 }
 231
 232 void kvm_exit_anon_inodes(void)
 233 {
 234 }
 235
 236 #undef anon_inode_getfd
 237
 238 #if LINUX_VERSION_CODE < KERNEL_VERSION(2,6,26) && !defined(RHEL_ANON_INODES)
 239
 240 int kvm_anon_inode_getfd(const char *name,
 241                          const struct file_operations *fops,
 242                          void *priv, int flags)
 243 {
 244         int r;
 245         int fd;
 246         struct inode *inode;
 247         struct file *file;
 248
 249         r = anon_inode_getfd(&fd, &inode, &file, name, fops, priv);
 250         if (r < 0)
 251                 return r;
 252         return fd;
 253 }
 254
 255 #elif LINUX_VERSION_CODE == KERNEL_VERSION(2,6,26) && !defined(RHEL_ANON_INODES)
 256
 257 int kvm_anon_inode_getfd(const char *name,
 258                          const struct file_operations *fops,
 259                          void *priv, int flags)
 260 {
 261         return anon_inode_getfd(name, fops, priv);
 262 }
 263
 264 #else
 265
 266 int kvm_anon_inode_getfd(const char *name,
 267                          const struct file_operations *fops,
 268                          void *priv, int flags)
 269 {
 270         return anon_inode_getfd(name, fops, priv, flags);
 271 }
 272
 273 #endif
 274
 275 #endif