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)
  66 {
  67         struct kernfs_super_info *info = kernfs_info(sb);
  68         struct inode *inode;
  69         struct dentry *root;
  70
  71         sb->s_blocksize = PAGE_CACHE_SIZE;
  72         sb->s_blocksize_bits = PAGE_CACHE_SHIFT;
  73         sb->s_magic = SYSFS_MAGIC;
  74         sb->s_op = &kernfs_sops;
  75         sb->s_time_gran = 1;
  76
  77         /* get root inode, initialize and unlock it */
  78         mutex_lock(&kernfs_mutex);
  79         inode = kernfs_get_inode(sb, info->root->kn);
  80         mutex_unlock(&kernfs_mutex);
  81         if (!inode) {
  82                 pr_debug("kernfs: could not get root inode\n");
  83                 return -ENOMEM;
  84         }
  85
  86         /* instantiate and link root dentry */
  87         root = d_make_root(inode);
  88         if (!root) {
  89                 pr_debug("%s: could not get root dentry!\n", __func__);
  90                 return -ENOMEM;
  91         }
  92         kernfs_get(info->root->kn);
  93         root->d_fsdata = info->root->kn;
  94         sb->s_root = root;
  95         sb->s_d_op = &kernfs_dops;
  96         return 0;
  97 }
  98
  99 static int kernfs_test_super(struct super_block *sb, void *data)
 100 {
 101         struct kernfs_super_info *sb_info = kernfs_info(sb);
 102         struct kernfs_super_info *info = data;
 103
 104         return sb_info->root == info->root && sb_info->ns == info->ns;
 105 }
 106
 107 static int kernfs_set_super(struct super_block *sb, void *data)
 108 {
 109         int error;
 110         error = set_anon_super(sb, data);
 111         if (!error)
 112                 sb->s_fs_info = data;
 113         return error;
 114 }
 115
 116 /**
 117  * kernfs_super_ns - determine the namespace tag of a kernfs super_block
 118  * @sb: super_block of interest
 119  *
 120  * Return the namespace tag associated with kernfs super_block @sb.
 121  */
 122 const void *kernfs_super_ns(struct super_block *sb)
 123 {
 124         struct kernfs_super_info *info = kernfs_info(sb);
 125
 126         return info->ns;
 127 }
 128
 129 /**
 130  * kernfs_mount_ns - kernfs mount helper
 131  * @fs_type: file_system_type of the fs being mounted
 132  * @flags: mount flags specified for the mount
 133  * @root: kernfs_root of the hierarchy being mounted
 134  * @new_sb_created: tell the caller if we allocated a new superblock
 135  * @ns: optional namespace tag of the mount
 136  *
 137  * This is to be called from each kernfs user's file_system_type->mount()
 138  * implementation, which should pass through the specified @fs_type and
 139  * @flags, and specify the hierarchy and namespace tag to mount via @root
 140  * and @ns, respectively.
 141  *
 142  * The return value can be passed to the vfs layer verbatim.
 143  */
 144 struct dentry *kernfs_mount_ns(struct file_system_type *fs_type, int flags,
 145                                struct kernfs_root *root, bool *new_sb_created,
 146                                const void *ns)
 147 {
 148         struct super_block *sb;
 149         struct kernfs_super_info *info;
 150         int error;
 151
 152         info = kzalloc(sizeof(*info), GFP_KERNEL);
 153         if (!info)
 154                 return ERR_PTR(-ENOMEM);
 155
 156         info->root = root;
 157         info->ns = ns;
 158
 159         sb = sget(fs_type, kernfs_test_super, kernfs_set_super, flags, info);
 160         if (IS_ERR(sb) || sb->s_fs_info != info)
 161                 kfree(info);
 162         if (IS_ERR(sb))
 163                 return ERR_CAST(sb);
 164
 165         if (new_sb_created)
 166                 *new_sb_created = !sb->s_root;
 167
 168         if (!sb->s_root) {
 169                 error = kernfs_fill_super(sb);
 170                 if (error) {
 171                         deactivate_locked_super(sb);
 172                         return ERR_PTR(error);
 173                 }
 174                 sb->s_flags |= MS_ACTIVE;
 175         }
 176
 177         return dget(sb->s_root);
 178 }
 179
 180 /**
 181  * kernfs_kill_sb - kill_sb for kernfs
 182  * @sb: super_block being killed
 183  *
 184  * This can be used directly for file_system_type->kill_sb().  If a kernfs
 185  * user needs extra cleanup, it can implement its own kill_sb() and call
 186  * this function at the end.
 187  */
 188 void kernfs_kill_sb(struct super_block *sb)
 189 {
 190         struct kernfs_super_info *info = kernfs_info(sb);
 191         struct kernfs_node *root_kn = sb->s_root->d_fsdata;
 192
 193         /*
 194          * Remove the superblock from fs_supers/s_instances
 195          * so we can't find it, before freeing kernfs_super_info.
 196          */
 197         kill_anon_super(sb);
 198         kfree(info);
 199         kernfs_put(root_kn);
 200 }
 201
 202 void __init kernfs_init(void)
 203 {
 204         kernfs_node_cache = kmem_cache_create("kernfs_node_cache",
 205                                               sizeof(struct kernfs_node),
 206                                               0, SLAB_PANIC, NULL);
 207         kernfs_inode_init();
 208 }