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![Steven Rostedt (VMware)](/assets/img/avatar_default.png)
The tracefs file system is by default mounted such that only root user can access it. But there are legitimate reasons to create a group and allow those added to the group to have access to tracing. By changing the permissions of the tracefs mount point to allow access, it will allow group access to the tracefs directory. There should not be any real reason to allow all access to the tracefs directory as it contains sensitive information. Have the default permission of directories being created not have any OTH (other) bits set, such that an admin that wants to give permission to a group has to first disable all OTH bits in the file system. Link: https://lkml.kernel.org/r/20210818153038.664127804@goodmis.org Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
553 lines
14 KiB
C
553 lines
14 KiB
C
// SPDX-License-Identifier: GPL-2.0-only
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/*
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* inode.c - part of tracefs, a pseudo file system for activating tracing
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*
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* Based on debugfs by: Greg Kroah-Hartman <greg@kroah.com>
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*
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* Copyright (C) 2014 Red Hat Inc, author: Steven Rostedt <srostedt@redhat.com>
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*
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* tracefs is the file system that is used by the tracing infrastructure.
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*/
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#include <linux/module.h>
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#include <linux/fs.h>
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#include <linux/mount.h>
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#include <linux/kobject.h>
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#include <linux/namei.h>
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#include <linux/tracefs.h>
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#include <linux/fsnotify.h>
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#include <linux/security.h>
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#include <linux/seq_file.h>
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#include <linux/parser.h>
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#include <linux/magic.h>
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#include <linux/slab.h>
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#define TRACEFS_DEFAULT_MODE 0700
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static struct vfsmount *tracefs_mount;
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static int tracefs_mount_count;
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static bool tracefs_registered;
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static ssize_t default_read_file(struct file *file, char __user *buf,
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size_t count, loff_t *ppos)
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{
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return 0;
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}
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static ssize_t default_write_file(struct file *file, const char __user *buf,
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size_t count, loff_t *ppos)
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{
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return count;
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}
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static const struct file_operations tracefs_file_operations = {
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.read = default_read_file,
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.write = default_write_file,
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.open = simple_open,
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.llseek = noop_llseek,
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};
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static struct tracefs_dir_ops {
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int (*mkdir)(const char *name);
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int (*rmdir)(const char *name);
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} tracefs_ops __ro_after_init;
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static char *get_dname(struct dentry *dentry)
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{
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const char *dname;
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char *name;
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int len = dentry->d_name.len;
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dname = dentry->d_name.name;
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name = kmalloc(len + 1, GFP_KERNEL);
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if (!name)
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return NULL;
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memcpy(name, dname, len);
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name[len] = 0;
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return name;
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}
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static int tracefs_syscall_mkdir(struct user_namespace *mnt_userns,
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struct inode *inode, struct dentry *dentry,
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umode_t mode)
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{
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char *name;
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int ret;
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name = get_dname(dentry);
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if (!name)
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return -ENOMEM;
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/*
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* The mkdir call can call the generic functions that create
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* the files within the tracefs system. It is up to the individual
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* mkdir routine to handle races.
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*/
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inode_unlock(inode);
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ret = tracefs_ops.mkdir(name);
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inode_lock(inode);
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kfree(name);
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return ret;
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}
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static int tracefs_syscall_rmdir(struct inode *inode, struct dentry *dentry)
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{
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char *name;
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int ret;
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name = get_dname(dentry);
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if (!name)
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return -ENOMEM;
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/*
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* The rmdir call can call the generic functions that create
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* the files within the tracefs system. It is up to the individual
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* rmdir routine to handle races.
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* This time we need to unlock not only the parent (inode) but
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* also the directory that is being deleted.
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*/
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inode_unlock(inode);
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inode_unlock(dentry->d_inode);
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ret = tracefs_ops.rmdir(name);
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inode_lock_nested(inode, I_MUTEX_PARENT);
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inode_lock(dentry->d_inode);
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kfree(name);
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return ret;
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}
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static const struct inode_operations tracefs_dir_inode_operations = {
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.lookup = simple_lookup,
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.mkdir = tracefs_syscall_mkdir,
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.rmdir = tracefs_syscall_rmdir,
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};
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static struct inode *tracefs_get_inode(struct super_block *sb)
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{
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struct inode *inode = new_inode(sb);
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if (inode) {
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inode->i_ino = get_next_ino();
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inode->i_atime = inode->i_mtime = inode->i_ctime = current_time(inode);
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}
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return inode;
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}
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struct tracefs_mount_opts {
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kuid_t uid;
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kgid_t gid;
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umode_t mode;
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};
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enum {
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Opt_uid,
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Opt_gid,
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Opt_mode,
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Opt_err
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};
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static const match_table_t tokens = {
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{Opt_uid, "uid=%u"},
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{Opt_gid, "gid=%u"},
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{Opt_mode, "mode=%o"},
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{Opt_err, NULL}
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};
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struct tracefs_fs_info {
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struct tracefs_mount_opts mount_opts;
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};
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static int tracefs_parse_options(char *data, struct tracefs_mount_opts *opts)
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{
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substring_t args[MAX_OPT_ARGS];
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int option;
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int token;
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kuid_t uid;
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kgid_t gid;
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char *p;
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opts->mode = TRACEFS_DEFAULT_MODE;
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while ((p = strsep(&data, ",")) != NULL) {
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if (!*p)
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continue;
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token = match_token(p, tokens, args);
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switch (token) {
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case Opt_uid:
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if (match_int(&args[0], &option))
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return -EINVAL;
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uid = make_kuid(current_user_ns(), option);
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if (!uid_valid(uid))
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return -EINVAL;
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opts->uid = uid;
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break;
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case Opt_gid:
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if (match_int(&args[0], &option))
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return -EINVAL;
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gid = make_kgid(current_user_ns(), option);
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if (!gid_valid(gid))
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return -EINVAL;
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opts->gid = gid;
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break;
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case Opt_mode:
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if (match_octal(&args[0], &option))
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return -EINVAL;
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opts->mode = option & S_IALLUGO;
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break;
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/*
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* We might like to report bad mount options here;
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* but traditionally tracefs has ignored all mount options
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*/
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}
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}
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return 0;
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}
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static int tracefs_apply_options(struct super_block *sb)
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{
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struct tracefs_fs_info *fsi = sb->s_fs_info;
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struct inode *inode = sb->s_root->d_inode;
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struct tracefs_mount_opts *opts = &fsi->mount_opts;
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inode->i_mode &= ~S_IALLUGO;
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inode->i_mode |= opts->mode;
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inode->i_uid = opts->uid;
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inode->i_gid = opts->gid;
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return 0;
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}
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static int tracefs_remount(struct super_block *sb, int *flags, char *data)
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{
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int err;
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struct tracefs_fs_info *fsi = sb->s_fs_info;
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sync_filesystem(sb);
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err = tracefs_parse_options(data, &fsi->mount_opts);
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if (err)
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goto fail;
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tracefs_apply_options(sb);
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fail:
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return err;
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}
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static int tracefs_show_options(struct seq_file *m, struct dentry *root)
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{
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struct tracefs_fs_info *fsi = root->d_sb->s_fs_info;
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struct tracefs_mount_opts *opts = &fsi->mount_opts;
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if (!uid_eq(opts->uid, GLOBAL_ROOT_UID))
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seq_printf(m, ",uid=%u",
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from_kuid_munged(&init_user_ns, opts->uid));
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if (!gid_eq(opts->gid, GLOBAL_ROOT_GID))
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seq_printf(m, ",gid=%u",
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from_kgid_munged(&init_user_ns, opts->gid));
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if (opts->mode != TRACEFS_DEFAULT_MODE)
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seq_printf(m, ",mode=%o", opts->mode);
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return 0;
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}
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static const struct super_operations tracefs_super_operations = {
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.statfs = simple_statfs,
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.remount_fs = tracefs_remount,
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.show_options = tracefs_show_options,
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};
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static int trace_fill_super(struct super_block *sb, void *data, int silent)
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{
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static const struct tree_descr trace_files[] = {{""}};
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struct tracefs_fs_info *fsi;
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int err;
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fsi = kzalloc(sizeof(struct tracefs_fs_info), GFP_KERNEL);
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sb->s_fs_info = fsi;
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if (!fsi) {
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err = -ENOMEM;
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goto fail;
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}
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err = tracefs_parse_options(data, &fsi->mount_opts);
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if (err)
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goto fail;
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err = simple_fill_super(sb, TRACEFS_MAGIC, trace_files);
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if (err)
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goto fail;
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sb->s_op = &tracefs_super_operations;
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tracefs_apply_options(sb);
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return 0;
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fail:
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kfree(fsi);
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sb->s_fs_info = NULL;
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return err;
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}
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static struct dentry *trace_mount(struct file_system_type *fs_type,
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int flags, const char *dev_name,
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void *data)
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{
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return mount_single(fs_type, flags, data, trace_fill_super);
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}
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static struct file_system_type trace_fs_type = {
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.owner = THIS_MODULE,
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.name = "tracefs",
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.mount = trace_mount,
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.kill_sb = kill_litter_super,
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};
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MODULE_ALIAS_FS("tracefs");
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static struct dentry *start_creating(const char *name, struct dentry *parent)
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{
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struct dentry *dentry;
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int error;
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pr_debug("tracefs: creating file '%s'\n",name);
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error = simple_pin_fs(&trace_fs_type, &tracefs_mount,
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&tracefs_mount_count);
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if (error)
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return ERR_PTR(error);
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/* If the parent is not specified, we create it in the root.
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* We need the root dentry to do this, which is in the super
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* block. A pointer to that is in the struct vfsmount that we
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* have around.
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*/
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if (!parent)
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parent = tracefs_mount->mnt_root;
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inode_lock(parent->d_inode);
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if (unlikely(IS_DEADDIR(parent->d_inode)))
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dentry = ERR_PTR(-ENOENT);
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else
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dentry = lookup_one_len(name, parent, strlen(name));
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if (!IS_ERR(dentry) && dentry->d_inode) {
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dput(dentry);
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dentry = ERR_PTR(-EEXIST);
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}
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if (IS_ERR(dentry)) {
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inode_unlock(parent->d_inode);
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simple_release_fs(&tracefs_mount, &tracefs_mount_count);
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}
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return dentry;
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}
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static struct dentry *failed_creating(struct dentry *dentry)
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{
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inode_unlock(dentry->d_parent->d_inode);
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dput(dentry);
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simple_release_fs(&tracefs_mount, &tracefs_mount_count);
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return NULL;
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}
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static struct dentry *end_creating(struct dentry *dentry)
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{
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inode_unlock(dentry->d_parent->d_inode);
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return dentry;
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}
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/**
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* tracefs_create_file - create a file in the tracefs filesystem
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* @name: a pointer to a string containing the name of the file to create.
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* @mode: the permission that the file should have.
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* @parent: a pointer to the parent dentry for this file. This should be a
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* directory dentry if set. If this parameter is NULL, then the
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* file will be created in the root of the tracefs filesystem.
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* @data: a pointer to something that the caller will want to get to later
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* on. The inode.i_private pointer will point to this value on
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* the open() call.
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* @fops: a pointer to a struct file_operations that should be used for
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* this file.
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*
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* This is the basic "create a file" function for tracefs. It allows for a
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* wide range of flexibility in creating a file, or a directory (if you want
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* to create a directory, the tracefs_create_dir() function is
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* recommended to be used instead.)
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*
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* This function will return a pointer to a dentry if it succeeds. This
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* pointer must be passed to the tracefs_remove() function when the file is
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* to be removed (no automatic cleanup happens if your module is unloaded,
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* you are responsible here.) If an error occurs, %NULL will be returned.
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*
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* If tracefs is not enabled in the kernel, the value -%ENODEV will be
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* returned.
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*/
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struct dentry *tracefs_create_file(const char *name, umode_t mode,
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struct dentry *parent, void *data,
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const struct file_operations *fops)
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{
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struct dentry *dentry;
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struct inode *inode;
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if (security_locked_down(LOCKDOWN_TRACEFS))
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return NULL;
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if (!(mode & S_IFMT))
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mode |= S_IFREG;
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BUG_ON(!S_ISREG(mode));
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dentry = start_creating(name, parent);
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if (IS_ERR(dentry))
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return NULL;
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inode = tracefs_get_inode(dentry->d_sb);
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if (unlikely(!inode))
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return failed_creating(dentry);
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inode->i_mode = mode;
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inode->i_fop = fops ? fops : &tracefs_file_operations;
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inode->i_private = data;
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d_instantiate(dentry, inode);
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fsnotify_create(dentry->d_parent->d_inode, dentry);
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return end_creating(dentry);
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}
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static struct dentry *__create_dir(const char *name, struct dentry *parent,
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const struct inode_operations *ops)
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{
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struct dentry *dentry = start_creating(name, parent);
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struct inode *inode;
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if (IS_ERR(dentry))
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return NULL;
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inode = tracefs_get_inode(dentry->d_sb);
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if (unlikely(!inode))
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return failed_creating(dentry);
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/* Do not set bits for OTH */
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inode->i_mode = S_IFDIR | S_IRWXU | S_IRUSR| S_IRGRP | S_IXUSR | S_IXGRP;
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inode->i_op = ops;
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inode->i_fop = &simple_dir_operations;
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/* directory inodes start off with i_nlink == 2 (for "." entry) */
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inc_nlink(inode);
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d_instantiate(dentry, inode);
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inc_nlink(dentry->d_parent->d_inode);
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fsnotify_mkdir(dentry->d_parent->d_inode, dentry);
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return end_creating(dentry);
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}
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/**
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* tracefs_create_dir - create a directory in the tracefs filesystem
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* @name: a pointer to a string containing the name of the directory to
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* create.
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* @parent: a pointer to the parent dentry for this file. This should be a
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* directory dentry if set. If this parameter is NULL, then the
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* directory will be created in the root of the tracefs filesystem.
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*
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* This function creates a directory in tracefs with the given name.
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*
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* This function will return a pointer to a dentry if it succeeds. This
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* pointer must be passed to the tracefs_remove() function when the file is
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* to be removed. If an error occurs, %NULL will be returned.
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*
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* If tracing is not enabled in the kernel, the value -%ENODEV will be
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* returned.
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*/
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struct dentry *tracefs_create_dir(const char *name, struct dentry *parent)
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{
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return __create_dir(name, parent, &simple_dir_inode_operations);
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}
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/**
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* tracefs_create_instance_dir - create the tracing instances directory
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* @name: The name of the instances directory to create
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* @parent: The parent directory that the instances directory will exist
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* @mkdir: The function to call when a mkdir is performed.
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* @rmdir: The function to call when a rmdir is performed.
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*
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* Only one instances directory is allowed.
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*
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* The instances directory is special as it allows for mkdir and rmdir to
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* to be done by userspace. When a mkdir or rmdir is performed, the inode
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* locks are released and the methods passed in (@mkdir and @rmdir) are
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* called without locks and with the name of the directory being created
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* within the instances directory.
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*
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* Returns the dentry of the instances directory.
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*/
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__init struct dentry *tracefs_create_instance_dir(const char *name,
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struct dentry *parent,
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int (*mkdir)(const char *name),
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int (*rmdir)(const char *name))
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{
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struct dentry *dentry;
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/* Only allow one instance of the instances directory. */
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if (WARN_ON(tracefs_ops.mkdir || tracefs_ops.rmdir))
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return NULL;
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dentry = __create_dir(name, parent, &tracefs_dir_inode_operations);
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if (!dentry)
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return NULL;
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tracefs_ops.mkdir = mkdir;
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tracefs_ops.rmdir = rmdir;
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return dentry;
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}
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static void remove_one(struct dentry *victim)
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{
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simple_release_fs(&tracefs_mount, &tracefs_mount_count);
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}
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/**
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* tracefs_remove - recursively removes a directory
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* @dentry: a pointer to a the dentry of the directory to be removed.
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*
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* This function recursively removes a directory tree in tracefs that
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* was previously created with a call to another tracefs function
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* (like tracefs_create_file() or variants thereof.)
|
|
*/
|
|
void tracefs_remove(struct dentry *dentry)
|
|
{
|
|
if (IS_ERR_OR_NULL(dentry))
|
|
return;
|
|
|
|
simple_pin_fs(&trace_fs_type, &tracefs_mount, &tracefs_mount_count);
|
|
simple_recursive_removal(dentry, remove_one);
|
|
simple_release_fs(&tracefs_mount, &tracefs_mount_count);
|
|
}
|
|
|
|
/**
|
|
* tracefs_initialized - Tells whether tracefs has been registered
|
|
*/
|
|
bool tracefs_initialized(void)
|
|
{
|
|
return tracefs_registered;
|
|
}
|
|
|
|
static int __init tracefs_init(void)
|
|
{
|
|
int retval;
|
|
|
|
retval = sysfs_create_mount_point(kernel_kobj, "tracing");
|
|
if (retval)
|
|
return -EINVAL;
|
|
|
|
retval = register_filesystem(&trace_fs_type);
|
|
if (!retval)
|
|
tracefs_registered = true;
|
|
|
|
return retval;
|
|
}
|
|
core_initcall(tracefs_init);
|