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); 179 180