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 const struct super_operations kernfs_sops = {
  23         .statfs         = simple_statfs,
  24         .drop_inode     = generic_delete_inode,
  25         .evict_inode    = kernfs_evict_inode,
  26 };
  27
  28 static int kernfs_fill_super(struct super_block *sb)
  29 {
  30         struct kernfs_super_info *info = kernfs_info(sb);
  31         struct inode *inode;
  32         struct dentry *root;
  33
  34         sb->s_blocksize = PAGE_CACHE_SIZE;
  35         sb->s_blocksize_bits = PAGE_CACHE_SHIFT;
  36         sb->s_magic = SYSFS_MAGIC;
  37         sb->s_op = &kernfs_sops;
  38         sb->s_time_gran = 1;
  39
  40         /* get root inode, initialize and unlock it */
  41         mutex_lock(&kernfs_mutex);
  42         inode = kernfs_get_inode(sb, info->root->kn);
  43         mutex_unlock(&kernfs_mutex);
  44         if (!inode) {
  45                 pr_debug("kernfs: could not get root inode\n");
  46                 return -ENOMEM;
  47         }
  48
  49         /* instantiate and link root dentry */
  50         root = d_make_root(inode);
  51         if (!root) {
  52                 pr_debug("%s: could not get root dentry!\n", __func__);
  53                 return -ENOMEM;
  54         }
  55         kernfs_get(info->root->kn);
  56         root->d_fsdata = info->root->kn;
  57         sb->s_root = root;
  58         sb->s_d_op = &kernfs_dops;
  59         return 0;
  60 }
  61
  62 static int kernfs_test_super(struct super_block *sb, void *data)
  63 {
  64         struct kernfs_super_info *sb_info = kernfs_info(sb);
  65         struct kernfs_super_info *info = data;
  66
  67         return sb_info->root == info->root && sb_info->ns == info->ns;
  68 }
  69
  70 static int kernfs_set_super(struct super_block *sb, void *data)
  71 {
  72         int error;
  73         error = set_anon_super(sb, data);
  74         if (!error)
  75                 sb->s_fs_info = data;
  76         return error;
  77 }
  78
  79 /**
  80  * kernfs_super_ns - determine the namespace tag of a kernfs super_block
  81  * @sb: super_block of interest
  82  *
  83  * Return the namespace tag associated with kernfs super_block @sb.
  84  */
  85 const void *kernfs_super_ns(struct super_block *sb)
  86 {
  87         struct kernfs_super_info *info = kernfs_info(sb);
  88
  89         return info->ns;
  90 }
  91
  92 /**
  93  * kernfs_mount_ns - kernfs mount helper
  94  * @fs_type: file_system_type of the fs being mounted
  95  * @flags: mount flags specified for the mount
  96  * @root: kernfs_root of the hierarchy being mounted
  97  * @new_sb_created: tell the caller if we allocated a new superblock
  98  * @ns: optional namespace tag of the mount
  99  *
 100  * This is to be called from each kernfs user's file_system_type->mount()
 101  * implementation, which should pass through the specified @fs_type and
 102  * @flags, and specify the hierarchy and namespace tag to mount via @root
 103  * and @ns, respectively.
 104  *
 105  * The return value can be passed to the vfs layer verbatim.
 106  */
 107 struct dentry *kernfs_mount_ns(struct file_system_type *fs_type, int flags,
 108                                struct kernfs_root *root, bool *new_sb_created,
 109                                const void *ns)
 110 {
 111         struct super_block *sb;
 112         struct kernfs_super_info *info;
 113         int error;
 114
 115         info = kzalloc(sizeof(*info), GFP_KERNEL);
 116         if (!info)
 117                 return ERR_PTR(-ENOMEM);
 118
 119         info->root = root;
 120         info->ns = ns;
 121
 122         sb = sget(fs_type, kernfs_test_super, kernfs_set_super, flags, info);
 123         if (IS_ERR(sb) || sb->s_fs_info != info)
 124                 kfree(info);
 125         if (IS_ERR(sb))
 126                 return ERR_CAST(sb);
 127
 128         if (new_sb_created)
 129                 *new_sb_created = !sb->s_root;
 130
 131         if (!sb->s_root) {
 132                 error = kernfs_fill_super(sb);
 133                 if (error) {
 134                         deactivate_locked_super(sb);
 135                         return ERR_PTR(error);
 136                 }
 137                 sb->s_flags |= MS_ACTIVE;
 138         }
 139
 140         return dget(sb->s_root);
 141 }
 142
 143 /**
 144  * kernfs_kill_sb - kill_sb for kernfs
 145  * @sb: super_block being killed
 146  *
 147  * This can be used directly for file_system_type->kill_sb().  If a kernfs
 148  * user needs extra cleanup, it can implement its own kill_sb() and call
 149  * this function at the end.
 150  */
 151 void kernfs_kill_sb(struct super_block *sb)
 152 {
 153         struct kernfs_super_info *info = kernfs_info(sb);
 154         struct kernfs_node *root_kn = sb->s_root->d_fsdata;
 155
 156         /*
 157          * Remove the superblock from fs_supers/s_instances
 158          * so we can't find it, before freeing kernfs_super_info.
 159          */
 160         kill_anon_super(sb);
 161         kfree(info);
 162         kernfs_put(root_kn);
 163 }
 164
 165 void __init kernfs_init(void)
 166 {
 167         kernfs_node_cache = kmem_cache_create("kernfs_node_cache",
 168                                               sizeof(struct kernfs_node),
 169                                               0, SLAB_PANIC, NULL);
 170         kernfs_inode_init();
 171 }