| 1 | /* |
| 2 | * fs/anon_inodes.c |
| 3 | * |
| 4 | * Copyright (C) 2007 Davide Libenzi <davidel@xmailserver.org> |
| 5 | * |
| 6 | * Thanks to Arnd Bergmann for code review and suggestions. |
| 7 | * More changes for Thomas Gleixner suggestions. |
| 8 | * |
| 9 | */ |
| 10 | |
| 11 | #include <linux/cred.h> |
| 12 | #include <linux/file.h> |
| 13 | #include <linux/poll.h> |
| 14 | #include <linux/sched.h> |
| 15 | #include <linux/init.h> |
| 16 | #include <linux/fs.h> |
| 17 | #include <linux/mount.h> |
| 18 | #include <linux/module.h> |
| 19 | #include <linux/kernel.h> |
| 20 | #include <linux/magic.h> |
| 21 | #include <linux/anon_inodes.h> |
| 22 | |
| 23 | #include <asm/uaccess.h> |
| 24 | |
| 25 | static struct vfsmount *anon_inode_mnt __read_mostly; |
| 26 | static struct inode *anon_inode_inode; |
| 27 | |
| 28 | /* |
| 29 | * anon_inodefs_dname() is called from d_path(). |
| 30 | */ |
| 31 | static char *anon_inodefs_dname(struct dentry *dentry, char *buffer, int buflen) |
| 32 | { |
| 33 | return dynamic_dname(dentry, buffer, buflen, "anon_inode:%s", |
| 34 | dentry->d_name.name); |
| 35 | } |
| 36 | |
| 37 | static const struct dentry_operations anon_inodefs_dentry_operations = { |
| 38 | .d_dname = anon_inodefs_dname, |
| 39 | }; |
| 40 | |
| 41 | static struct dentry *anon_inodefs_mount(struct file_system_type *fs_type, |
| 42 | int flags, const char *dev_name, void *data) |
| 43 | { |
| 44 | return mount_pseudo(fs_type, "anon_inode:", NULL, |
| 45 | &anon_inodefs_dentry_operations, ANON_INODE_FS_MAGIC); |
| 46 | } |
| 47 | |
| 48 | static struct file_system_type anon_inode_fs_type = { |
| 49 | .name = "anon_inodefs", |
| 50 | .mount = anon_inodefs_mount, |
| 51 | .kill_sb = kill_anon_super, |
| 52 | }; |
| 53 | |
| 54 | /** |
| 55 | * anon_inode_getfile - creates a new file instance by hooking it up to an |
| 56 | * anonymous inode, and a dentry that describe the "class" |
| 57 | * of the file |
| 58 | * |
| 59 | * @name: [in] name of the "class" of the new file |
| 60 | * @fops: [in] file operations for the new file |
| 61 | * @priv: [in] private data for the new file (will be file's private_data) |
| 62 | * @flags: [in] flags |
| 63 | * |
| 64 | * Creates a new file by hooking it on a single inode. This is useful for files |
| 65 | * that do not need to have a full-fledged inode in order to operate correctly. |
| 66 | * All the files created with anon_inode_getfile() will share a single inode, |
| 67 | * hence saving memory and avoiding code duplication for the file/inode/dentry |
| 68 | * setup. Returns the newly created file* or an error pointer. |
| 69 | */ |
| 70 | struct file *anon_inode_getfile(const char *name, |
| 71 | const struct file_operations *fops, |
| 72 | void *priv, int flags) |
| 73 | { |
| 74 | struct qstr this; |
| 75 | struct path path; |
| 76 | struct file *file; |
| 77 | |
| 78 | if (IS_ERR(anon_inode_inode)) |
| 79 | return ERR_PTR(-ENODEV); |
| 80 | |
| 81 | if (fops->owner && !try_module_get(fops->owner)) |
| 82 | return ERR_PTR(-ENOENT); |
| 83 | |
| 84 | /* |
| 85 | * Link the inode to a directory entry by creating a unique name |
| 86 | * using the inode sequence number. |
| 87 | */ |
| 88 | file = ERR_PTR(-ENOMEM); |
| 89 | this.name = name; |
| 90 | this.len = strlen(name); |
| 91 | this.hash = 0; |
| 92 | path.dentry = d_alloc_pseudo(anon_inode_mnt->mnt_sb, &this); |
| 93 | if (!path.dentry) |
| 94 | goto err_module; |
| 95 | |
| 96 | path.mnt = mntget(anon_inode_mnt); |
| 97 | /* |
| 98 | * We know the anon_inode inode count is always greater than zero, |
| 99 | * so ihold() is safe. |
| 100 | */ |
| 101 | ihold(anon_inode_inode); |
| 102 | |
| 103 | d_instantiate(path.dentry, anon_inode_inode); |
| 104 | |
| 105 | file = alloc_file(&path, OPEN_FMODE(flags), fops); |
| 106 | if (IS_ERR(file)) |
| 107 | goto err_dput; |
| 108 | file->f_mapping = anon_inode_inode->i_mapping; |
| 109 | |
| 110 | file->f_flags = flags & (O_ACCMODE | O_NONBLOCK); |
| 111 | file->private_data = priv; |
| 112 | |
| 113 | return file; |
| 114 | |
| 115 | err_dput: |
| 116 | path_put(&path); |
| 117 | err_module: |
| 118 | module_put(fops->owner); |
| 119 | return file; |
| 120 | } |
| 121 | EXPORT_SYMBOL_GPL(anon_inode_getfile); |
| 122 | |
| 123 | /** |
| 124 | * anon_inode_getfd - creates a new file instance by hooking it up to an |
| 125 | * anonymous inode, and a dentry that describe the "class" |
| 126 | * of the file |
| 127 | * |
| 128 | * @name: [in] name of the "class" of the new file |
| 129 | * @fops: [in] file operations for the new file |
| 130 | * @priv: [in] private data for the new file (will be file's private_data) |
| 131 | * @flags: [in] flags |
| 132 | * |
| 133 | * Creates a new file by hooking it on a single inode. This is useful for files |
| 134 | * that do not need to have a full-fledged inode in order to operate correctly. |
| 135 | * All the files created with anon_inode_getfd() will share a single inode, |
| 136 | * hence saving memory and avoiding code duplication for the file/inode/dentry |
| 137 | * setup. Returns new descriptor or an error code. |
| 138 | */ |
| 139 | int anon_inode_getfd(const char *name, const struct file_operations *fops, |
| 140 | void *priv, int flags) |
| 141 | { |
| 142 | int error, fd; |
| 143 | struct file *file; |
| 144 | |
| 145 | error = get_unused_fd_flags(flags); |
| 146 | if (error < 0) |
| 147 | return error; |
| 148 | fd = error; |
| 149 | |
| 150 | file = anon_inode_getfile(name, fops, priv, flags); |
| 151 | if (IS_ERR(file)) { |
| 152 | error = PTR_ERR(file); |
| 153 | goto err_put_unused_fd; |
| 154 | } |
| 155 | fd_install(fd, file); |
| 156 | |
| 157 | return fd; |
| 158 | |
| 159 | err_put_unused_fd: |
| 160 | put_unused_fd(fd); |
| 161 | return error; |
| 162 | } |
| 163 | EXPORT_SYMBOL_GPL(anon_inode_getfd); |
| 164 | |
| 165 | static int __init anon_inode_init(void) |
| 166 | { |
| 167 | anon_inode_mnt = kern_mount(&anon_inode_fs_type); |
| 168 | if (IS_ERR(anon_inode_mnt)) |
| 169 | panic("anon_inode_init() kernel mount failed (%ld)\n", PTR_ERR(anon_inode_mnt)); |
| 170 | |
| 171 | anon_inode_inode = alloc_anon_inode(anon_inode_mnt->mnt_sb); |
| 172 | if (IS_ERR(anon_inode_inode)) |
| 173 | panic("anon_inode_init() inode allocation failed (%ld)\n", PTR_ERR(anon_inode_inode)); |
| 174 | |
| 175 | return 0; |
| 176 | } |
| 177 | |
| 178 | fs_initcall(anon_inode_init); |
| 179 | |