xref: /openbmc/linux/fs/kernfs/mount.c (revision d2999e1b)
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 void __init kernfs_init(void)
215 {
216 	kernfs_node_cache = kmem_cache_create("kernfs_node_cache",
217 					      sizeof(struct kernfs_node),
218 					      0, SLAB_PANIC, NULL);
219 	kernfs_inode_init();
220 }
221