1 // SPDX-License-Identifier: GPL-2.0-only 2 /* 3 * fs/anon_inodes.c 4 * 5 * Copyright (C) 2007 Davide Libenzi <davidel@xmailserver.org> 6 * 7 * Thanks to Arnd Bergmann for code review and suggestions. 8 * More changes for Thomas Gleixner suggestions. 9 * 10 */ 11 12 #include <linux/cred.h> 13 #include <linux/file.h> 14 #include <linux/poll.h> 15 #include <linux/sched.h> 16 #include <linux/init.h> 17 #include <linux/fs.h> 18 #include <linux/mount.h> 19 #include <linux/module.h> 20 #include <linux/kernel.h> 21 #include <linux/magic.h> 22 #include <linux/anon_inodes.h> 23 24 #include <linux/uaccess.h> 25 26 static struct vfsmount *anon_inode_mnt __read_mostly; 27 static struct inode *anon_inode_inode; 28 29 /* 30 * anon_inodefs_dname() is called from d_path(). 31 */ 32 static char *anon_inodefs_dname(struct dentry *dentry, char *buffer, int buflen) 33 { 34 return dynamic_dname(dentry, buffer, buflen, "anon_inode:%s", 35 dentry->d_name.name); 36 } 37 38 static const struct dentry_operations anon_inodefs_dentry_operations = { 39 .d_dname = anon_inodefs_dname, 40 }; 41 42 static struct dentry *anon_inodefs_mount(struct file_system_type *fs_type, 43 int flags, const char *dev_name, void *data) 44 { 45 return mount_pseudo(fs_type, "anon_inode:", NULL, 46 &anon_inodefs_dentry_operations, ANON_INODE_FS_MAGIC); 47 } 48 49 static struct file_system_type anon_inode_fs_type = { 50 .name = "anon_inodefs", 51 .mount = anon_inodefs_mount, 52 .kill_sb = kill_anon_super, 53 }; 54 55 /** 56 * anon_inode_getfile - creates a new file instance by hooking it up to an 57 * anonymous inode, and a dentry that describe the "class" 58 * of the file 59 * 60 * @name: [in] name of the "class" of the new file 61 * @fops: [in] file operations for the new file 62 * @priv: [in] private data for the new file (will be file's private_data) 63 * @flags: [in] flags 64 * 65 * Creates a new file by hooking it on a single inode. This is useful for files 66 * that do not need to have a full-fledged inode in order to operate correctly. 67 * All the files created with anon_inode_getfile() will share a single inode, 68 * hence saving memory and avoiding code duplication for the file/inode/dentry 69 * setup. Returns the newly created file* or an error pointer. 70 */ 71 struct file *anon_inode_getfile(const char *name, 72 const struct file_operations *fops, 73 void *priv, int flags) 74 { 75 struct file *file; 76 77 if (IS_ERR(anon_inode_inode)) 78 return ERR_PTR(-ENODEV); 79 80 if (fops->owner && !try_module_get(fops->owner)) 81 return ERR_PTR(-ENOENT); 82 83 /* 84 * We know the anon_inode inode count is always greater than zero, 85 * so ihold() is safe. 86 */ 87 ihold(anon_inode_inode); 88 file = alloc_file_pseudo(anon_inode_inode, anon_inode_mnt, name, 89 flags & (O_ACCMODE | O_NONBLOCK), fops); 90 if (IS_ERR(file)) 91 goto err; 92 93 file->f_mapping = anon_inode_inode->i_mapping; 94 95 file->private_data = priv; 96 97 return file; 98 99 err: 100 iput(anon_inode_inode); 101 module_put(fops->owner); 102 return file; 103 } 104 EXPORT_SYMBOL_GPL(anon_inode_getfile); 105 106 /** 107 * anon_inode_getfd - creates a new file instance by hooking it up to an 108 * anonymous inode, and a dentry that describe the "class" 109 * of the file 110 * 111 * @name: [in] name of the "class" of the new file 112 * @fops: [in] file operations for the new file 113 * @priv: [in] private data for the new file (will be file's private_data) 114 * @flags: [in] flags 115 * 116 * Creates a new file by hooking it on a single inode. This is useful for files 117 * that do not need to have a full-fledged inode in order to operate correctly. 118 * All the files created with anon_inode_getfd() will share a single inode, 119 * hence saving memory and avoiding code duplication for the file/inode/dentry 120 * setup. Returns new descriptor or an error code. 121 */ 122 int anon_inode_getfd(const char *name, const struct file_operations *fops, 123 void *priv, int flags) 124 { 125 int error, fd; 126 struct file *file; 127 128 error = get_unused_fd_flags(flags); 129 if (error < 0) 130 return error; 131 fd = error; 132 133 file = anon_inode_getfile(name, fops, priv, flags); 134 if (IS_ERR(file)) { 135 error = PTR_ERR(file); 136 goto err_put_unused_fd; 137 } 138 fd_install(fd, file); 139 140 return fd; 141 142 err_put_unused_fd: 143 put_unused_fd(fd); 144 return error; 145 } 146 EXPORT_SYMBOL_GPL(anon_inode_getfd); 147 148 static int __init anon_inode_init(void) 149 { 150 anon_inode_mnt = kern_mount(&anon_inode_fs_type); 151 if (IS_ERR(anon_inode_mnt)) 152 panic("anon_inode_init() kernel mount failed (%ld)\n", PTR_ERR(anon_inode_mnt)); 153 154 anon_inode_inode = alloc_anon_inode(anon_inode_mnt->mnt_sb); 155 if (IS_ERR(anon_inode_inode)) 156 panic("anon_inode_init() inode allocation failed (%ld)\n", PTR_ERR(anon_inode_inode)); 157 158 return 0; 159 } 160 161 fs_initcall(anon_inode_init); 162 163