xref: /linux/fs/kernfs/mount.c (revision 00a6d7b6762c27d441e9ac8faff36384bc0fc180)
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 }
209