fs/kernfs/mount.c

   1 /*
   2  * fs/kernfs/mount.c - kernfs mount implementation
   3  *
   4  * Copyright (c) 2001-3 Patrick Mochel
   5  * Copyright (c) 2007 SUSE Linux Products GmbH
   6  * Copyright (c) 2007, 2013 Tejun Heo <tj@kernel.org>
   7  *
   8  * This file is released under the GPLv2.
   9  */
  10
  11 #include <linux/fs.h>
  12 #include <linux/mount.h>
  13 #include <linux/init.h>
  14 #include <linux/magic.h>
  15 #include <linux/slab.h>
  16 #include <linux/pagemap.h>
  17
  18 #include "kernfs-internal.h"
  19
  20 struct kmem_cache *kernfs_node_cache;
  21
  22 static int kernfs_sop_remount_fs(struct super_block *sb, int *flags, char *data)
  23 {
  24         struct kernfs_root *root = kernfs_info(sb)->root;
  25         struct kernfs_syscall_ops *scops = root->syscall_ops;
  26
  27         if (scops && scops->remount_fs)
  28                 return scops->remount_fs(root, flags, data);
  29         return 0;
  30 }
  31
  32 static int kernfs_sop_show_options(struct seq_file *sf, struct dentry *dentry)
  33 {
  34         struct kernfs_root *root = kernfs_root(dentry->d_fsdata);
  35         struct kernfs_syscall_ops *scops = root->syscall_ops;
  36
  37         if (scops && scops->show_options)
  38                 return scops->show_options(sf, root);
  39         return 0;
  40 }
  41
  42 const struct super_operations kernfs_sops = {
  43         .statfs         = simple_statfs,
  44         .drop_inode     = generic_delete_inode,
  45         .evict_inode    = kernfs_evict_inode,
  46
  47         .remount_fs     = kernfs_sop_remount_fs,
  48         .show_options   = kernfs_sop_show_options,
  49 };
  50
  51 /**
  52  * kernfs_root_from_sb - determine kernfs_root associated with a super_block
  53  * @sb: the super_block in question
  54  *
  55  * Return the kernfs_root associated with @sb.  If @sb is not a kernfs one,
  56  * %NULL is returned.
  57  */
  58 struct kernfs_root *kernfs_root_from_sb(struct super_block *sb)
  59 {
  60         if (sb->s_op == &kernfs_sops)
  61                 return kernfs_info(sb)->root;
  62         return NULL;
  63 }
  64
  65 static int kernfs_fill_super(struct super_block *sb, unsigned long magic)
  66 {
  67         struct kernfs_super_info *info = kernfs_info(sb);
  68         struct inode *inode;
  69         struct dentry *root;
  70
  71         info->sb = sb;
  72         sb->s_blocksize = PAGE_CACHE_SIZE;
  73         sb->s_blocksize_bits = PAGE_CACHE_SHIFT;
  74         sb->s_magic = magic;
  75         sb->s_op = &kernfs_sops;
  76         sb->s_time_gran = 1;
  77
  78         /* get root inode, initialize and unlock it */
  79         mutex_lock(&kernfs_mutex);
  80         inode = kernfs_get_inode(sb, info->root->kn);
  81         mutex_unlock(&kernfs_mutex);
  82         if (!inode) {
  83                 pr_debug("kernfs: could not get root inode\n");
  84                 return -ENOMEM;
  85         }
  86
  87         /* instantiate and link root dentry */
  88         root = d_make_root(inode);
  89         if (!root) {
  90                 pr_debug("%s: could not get root dentry!\n", __func__);
  91                 return -ENOMEM;
  92         }
  93         kernfs_get(info->root->kn);
  94         root->d_fsdata = info->root->kn;
  95         sb->s_root = root;
  96         sb->s_d_op = &kernfs_dops;
  97         return 0;
  98 }
  99
 100 static int kernfs_test_super(struct super_block *sb, void *data)
 101 {
 102         struct kernfs_super_info *sb_info = kernfs_info(sb);
 103         struct kernfs_super_info *info = data;
 104
 105         return sb_info->root == info->root && sb_info->ns == info->ns;
 106 }
 107
 108 static int kernfs_set_super(struct super_block *sb, void *data)
 109 {
 110         int error;
 111         error = set_anon_super(sb, data);
 112         if (!error)
 113                 sb->s_fs_info = data;
 114         return error;
 115 }
 116
 117 /**
 118  * kernfs_super_ns - determine the namespace tag of a kernfs super_block
 119  * @sb: super_block of interest
 120  *
 121  * Return the namespace tag associated with kernfs super_block @sb.
 122  */
 123 const void *kernfs_super_ns(struct super_block *sb)
 124 {
 125         struct kernfs_super_info *info = kernfs_info(sb);
 126
 127         return info->ns;
 128 }
 129
 130 /**
 131  * kernfs_mount_ns - kernfs mount helper
 132  * @fs_type: file_system_type of the fs being mounted
 133  * @flags: mount flags specified for the mount
 134  * @root: kernfs_root of the hierarchy being mounted
 135  * @magic: file system specific magic number
 136  * @new_sb_created: tell the caller if we allocated a new superblock
 137  * @ns: optional namespace tag of the mount
 138  *
 139  * This is to be called from each kernfs user's file_system_type->mount()
 140  * implementation, which should pass through the specified @fs_type and
 141  * @flags, and specify the hierarchy and namespace tag to mount via @root
 142  * and @ns, respectively.
 143  *
 144  * The return value can be passed to the vfs layer verbatim.
 145  */
 146 struct dentry *kernfs_mount_ns(struct file_system_type *fs_type, int flags,
 147                                 struct kernfs_root *root, unsigned long magic,
 148                                 bool *new_sb_created, const void *ns)
 149 {
 150         struct super_block *sb;
 151         struct kernfs_super_info *info;
 152         int error;
 153
 154         info = kzalloc(sizeof(*info), GFP_KERNEL);
 155         if (!info)
 156                 return ERR_PTR(-ENOMEM);
 157
 158         info->root = root;
 159         info->ns = ns;
 160
 161         sb = sget(fs_type, kernfs_test_super, kernfs_set_super, flags, info);
 162         if (IS_ERR(sb) || sb->s_fs_info != info)
 163                 kfree(info);
 164         if (IS_ERR(sb))
 165                 return ERR_CAST(sb);
 166
 167         if (new_sb_created)
 168                 *new_sb_created = !sb->s_root;
 169
 170         if (!sb->s_root) {
 171                 struct kernfs_super_info *info = kernfs_info(sb);
 172
 173                 error = kernfs_fill_super(sb, magic);
 174                 if (error) {
 175                         deactivate_locked_super(sb);
 176                         return ERR_PTR(error);
 177                 }
 178                 sb->s_flags |= MS_ACTIVE;
 179
 180                 mutex_lock(&kernfs_mutex);
 181                 list_add(&info->node, &root->supers);
 182                 mutex_unlock(&kernfs_mutex);
 183         }
 184
 185         return dget(sb->s_root);
 186 }
 187
 188 /**
 189  * kernfs_kill_sb - kill_sb for kernfs
 190  * @sb: super_block being killed
 191  *
 192  * This can be used directly for file_system_type->kill_sb().  If a kernfs
 193  * user needs extra cleanup, it can implement its own kill_sb() and call
 194  * this function at the end.
 195  */
 196 void kernfs_kill_sb(struct super_block *sb)
 197 {
 198         struct kernfs_super_info *info = kernfs_info(sb);
 199         struct kernfs_node *root_kn = sb->s_root->d_fsdata;
 200
 201         mutex_lock(&kernfs_mutex);
 202         list_del(&info->node);
 203         mutex_unlock(&kernfs_mutex);
 204
 205         /*
 206          * Remove the superblock from fs_supers/s_instances
 207          * so we can't find it, before freeing kernfs_super_info.
 208          */
 209         kill_anon_super(sb);
 210         kfree(info);
 211         kernfs_put(root_kn);
 212 }
 213
 214 /**
 215  * kernfs_pin_sb: try to pin the superblock associated with a kernfs_root
 216  * @kernfs_root: the kernfs_root in question
 217  * @ns: the namespace tag
 218  *
 219  * Pin the superblock so the superblock won't be destroyed in subsequent
 220  * operations.  This can be used to block ->kill_sb() which may be useful
 221  * for kernfs users which dynamically manage superblocks.
 222  *
 223  * Returns NULL if there's no superblock associated to this kernfs_root, or
 224  * -EINVAL if the superblock is being freed.
 225  */
 226 struct super_block *kernfs_pin_sb(struct kernfs_root *root, const void *ns)
 227 {
 228         struct kernfs_super_info *info;
 229         struct super_block *sb = NULL;
 230
 231         mutex_lock(&kernfs_mutex);
 232         list_for_each_entry(info, &root->supers, node) {
 233                 if (info->ns == ns) {
 234                         sb = info->sb;
 235                         if (!atomic_inc_not_zero(&info->sb->s_active))
 236                                 sb = ERR_PTR(-EINVAL);
 237                         break;
 238                 }
 239         }
 240         mutex_unlock(&kernfs_mutex);
 241         return sb;
 242 }
 243
 244 void __init kernfs_init(void)
 245 {
 246         kernfs_node_cache = kmem_cache_create("kernfs_node_cache",
 247                                               sizeof(struct kernfs_node),
 248                                               0, SLAB_PANIC, NULL);
 249         kernfs_inode_init();
 250 }