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 #include <linux/pseudo_fs.h> 24 25 #include <linux/uaccess.h> 26 27 static struct vfsmount *anon_inode_mnt __read_mostly; 28 static struct inode *anon_inode_inode; 29 30 /* 31 * anon_inodefs_dname() is called from d_path(). 32 */ 33 static char *anon_inodefs_dname(struct dentry *dentry, char *buffer, int buflen) 34 { 35 return dynamic_dname(dentry, buffer, buflen, "anon_inode:%s", 36 dentry->d_name.name); 37 } 38 39 static const struct dentry_operations anon_inodefs_dentry_operations = { 40 .d_dname = anon_inodefs_dname, 41 }; 42 43 static int anon_inodefs_init_fs_context(struct fs_context *fc) 44 { 45 struct pseudo_fs_context *ctx = init_pseudo(fc, ANON_INODE_FS_MAGIC); 46 if (!ctx) 47 return -ENOMEM; 48 ctx->dops = &anon_inodefs_dentry_operations; 49 return 0; 50 } 51 52 static struct file_system_type anon_inode_fs_type = { 53 .name = "anon_inodefs", 54 .init_fs_context = anon_inodefs_init_fs_context, 55 .kill_sb = kill_anon_super, 56 }; 57 58 /** 59 * anon_inode_getfile - creates a new file instance by hooking it up to an 60 * anonymous inode, and a dentry that describe the "class" 61 * of the file 62 * 63 * @name: [in] name of the "class" of the new file 64 * @fops: [in] file operations for the new file 65 * @priv: [in] private data for the new file (will be file's private_data) 66 * @flags: [in] flags 67 * 68 * Creates a new file by hooking it on a single inode. This is useful for files 69 * that do not need to have a full-fledged inode in order to operate correctly. 70 * All the files created with anon_inode_getfile() will share a single inode, 71 * hence saving memory and avoiding code duplication for the file/inode/dentry 72 * setup. Returns the newly created file* or an error pointer. 73 */ 74 struct file *anon_inode_getfile(const char *name, 75 const struct file_operations *fops, 76 void *priv, int flags) 77 { 78 struct file *file; 79 80 if (IS_ERR(anon_inode_inode)) 81 return ERR_PTR(-ENODEV); 82 83 if (fops->owner && !try_module_get(fops->owner)) 84 return ERR_PTR(-ENOENT); 85 86 /* 87 * We know the anon_inode inode count is always greater than zero, 88 * so ihold() is safe. 89 */ 90 ihold(anon_inode_inode); 91 file = alloc_file_pseudo(anon_inode_inode, anon_inode_mnt, name, 92 flags & (O_ACCMODE | O_NONBLOCK), fops); 93 if (IS_ERR(file)) 94 goto err; 95 96 file->f_mapping = anon_inode_inode->i_mapping; 97 98 file->private_data = priv; 99 100 return file; 101 102 err: 103 iput(anon_inode_inode); 104 module_put(fops->owner); 105 return file; 106 } 107 EXPORT_SYMBOL_GPL(anon_inode_getfile); 108 109 /** 110 * anon_inode_getfd - creates a new file instance by hooking it up to an 111 * anonymous inode, and a dentry that describe the "class" 112 * of the file 113 * 114 * @name: [in] name of the "class" of the new file 115 * @fops: [in] file operations for the new file 116 * @priv: [in] private data for the new file (will be file's private_data) 117 * @flags: [in] flags 118 * 119 * Creates a new file by hooking it on a single inode. This is useful for files 120 * that do not need to have a full-fledged inode in order to operate correctly. 121 * All the files created with anon_inode_getfd() will share a single inode, 122 * hence saving memory and avoiding code duplication for the file/inode/dentry 123 * setup. Returns new descriptor or an error code. 124 */ 125 int anon_inode_getfd(const char *name, const struct file_operations *fops, 126 void *priv, int flags) 127 { 128 int error, fd; 129 struct file *file; 130 131 error = get_unused_fd_flags(flags); 132 if (error < 0) 133 return error; 134 fd = error; 135 136 file = anon_inode_getfile(name, fops, priv, flags); 137 if (IS_ERR(file)) { 138 error = PTR_ERR(file); 139 goto err_put_unused_fd; 140 } 141 fd_install(fd, file); 142 143 return fd; 144 145 err_put_unused_fd: 146 put_unused_fd(fd); 147 return error; 148 } 149 EXPORT_SYMBOL_GPL(anon_inode_getfd); 150 151 static int __init anon_inode_init(void) 152 { 153 anon_inode_mnt = kern_mount(&anon_inode_fs_type); 154 if (IS_ERR(anon_inode_mnt)) 155 panic("anon_inode_init() kernel mount failed (%ld)\n", PTR_ERR(anon_inode_mnt)); 156 157 anon_inode_inode = alloc_anon_inode(anon_inode_mnt->mnt_sb); 158 if (IS_ERR(anon_inode_inode)) 159 panic("anon_inode_init() inode allocation failed (%ld)\n", PTR_ERR(anon_inode_inode)); 160 161 return 0; 162 } 163 164 fs_initcall(anon_inode_init); 165 166