--- /dev/null
+/*
+ * dcookies.c
+ *
+ * Copyright 2002 John Levon <levon@movementarian.org>
+ *
+ * Persistent cookie-path mappings. These are used by
+ * profilers to convert a per-task EIP value into something
+ * non-transitory that can be processed at a later date.
+ * This is done by locking the dentry/vfsmnt pair in the
+ * kernel until released by the tasks needing the persistent
+ * objects. The tag is simply an unsigned long that refers
+ * to the pair and can be looked up from userspace.
+ */
+
+#include <linux/config.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/list.h>
+#include <linux/mount.h>
+#include <linux/dcache.h>
+#include <linux/mm.h>
+#include <linux/errno.h>
+#include <linux/dcookies.h>
+#include <asm/uaccess.h>
+
+/* The dcookies are allocated from a kmem_cache and
+ * hashed onto a small number of lists. None of the
+ * code here is particularly performance critical
+ */
+struct dcookie_struct {
+ struct dentry * dentry;
+ struct vfsmount * vfsmnt;
+ struct list_head hash_list;
+};
+
+static LIST_HEAD(dcookie_users);
+static DECLARE_MUTEX(dcookie_sem);
+static kmem_cache_t * dcookie_cache;
+static struct list_head * dcookie_hashtable;
+static size_t hash_size;
+
+static inline int is_live(void)
+{
+ return !(list_empty(&dcookie_users));
+}
+
+
+/* The dentry is locked, its address will do for the cookie */
+static inline unsigned long dcookie_value(struct dcookie_struct * dcs)
+{
+ return (unsigned long)dcs->dentry;
+}
+
+
+static size_t dcookie_hash(unsigned long dcookie)
+{
+ return (dcookie >> 2) & (hash_size - 1);
+}
+
+
+static struct dcookie_struct * find_dcookie(unsigned long dcookie)
+{
+ struct dcookie_struct * found = 0;
+ struct dcookie_struct * dcs;
+ struct list_head * pos;
+ struct list_head * list;
+
+ list = dcookie_hashtable + dcookie_hash(dcookie);
+
+ list_for_each(pos, list) {
+ dcs = list_entry(pos, struct dcookie_struct, hash_list);
+ if (dcookie_value(dcs) == dcookie) {
+ found = dcs;
+ break;
+ }
+ }
+
+ return found;
+}
+
+
+static void hash_dcookie(struct dcookie_struct * dcs)
+{
+ struct list_head * list = dcookie_hashtable + dcookie_hash(dcookie_value(dcs));
+ list_add(&dcs->hash_list, list);
+}
+
+
+static struct dcookie_struct * alloc_dcookie(struct dentry * dentry,
+ struct vfsmount * vfsmnt)
+{
+ struct dcookie_struct * dcs = kmem_cache_alloc(dcookie_cache, GFP_KERNEL);
+ if (!dcs)
+ return NULL;
+
+ atomic_inc(&dentry->d_count);
+ atomic_inc(&vfsmnt->mnt_count);
+ dentry->d_cookie = dcs;
+
+ dcs->dentry = dentry;
+ dcs->vfsmnt = vfsmnt;
+ hash_dcookie(dcs);
+
+ return dcs;
+}
+
+
+/* This is the main kernel-side routine that retrieves the cookie
+ * value for a dentry/vfsmnt pair.
+ */
+int get_dcookie(struct dentry * dentry, struct vfsmount * vfsmnt,
+ unsigned long * cookie)
+{
+ int err = 0;
+ struct dcookie_struct * dcs;
+
+ down(&dcookie_sem);
+
+ if (!is_live()) {
+ err = -EINVAL;
+ goto out;
+ }
+
+ dcs = dentry->d_cookie;
+
+ if (!dcs)
+ dcs = alloc_dcookie(dentry, vfsmnt);
+
+ if (!dcs) {
+ err = -ENOMEM;
+ goto out;
+ }
+
+ *cookie = dcookie_value(dcs);
+
+out:
+ up(&dcookie_sem);
+ return err;
+}
+
+
+/* And here is where the userspace process can look up the cookie value
+ * to retrieve the path.
+ */
+asmlinkage int sys_lookup_dcookie(unsigned long cookie, char * buf, size_t len)
+{
+ char * kbuf;
+ char * path;
+ int err = -EINVAL;
+ size_t pathlen;
+ struct dcookie_struct * dcs;
+
+ /* we could leak path information to users
+ * without dir read permission without this
+ */
+ if (!capable(CAP_SYS_ADMIN))
+ return -EPERM;
+
+ down(&dcookie_sem);
+
+ if (!is_live()) {
+ err = -EINVAL;
+ goto out;
+ }
+
+ if (!(dcs = find_dcookie(cookie)))
+ goto out;
+
+ err = -ENOMEM;
+ kbuf = kmalloc(PAGE_SIZE, GFP_KERNEL);
+ if (!kbuf)
+ goto out;
+ memset(kbuf, 0, PAGE_SIZE);
+
+ /* FIXME: (deleted) ? */
+ path = d_path(dcs->dentry, dcs->vfsmnt, kbuf, PAGE_SIZE);
+
+ err = 0;
+
+ pathlen = kbuf + PAGE_SIZE - path;
+ if (len > pathlen)
+ len = pathlen;
+
+ if (copy_to_user(buf, path, len))
+ err = -EFAULT;
+
+ kfree(kbuf);
+out:
+ up(&dcookie_sem);
+ return err;
+}
+
+
+static int dcookie_init(void)
+{
+ struct list_head * d;
+ unsigned int i, hash_bits;
+ int err = -ENOMEM;
+
+ dcookie_cache = kmem_cache_create("dcookie_cache",
+ sizeof(struct dcookie_struct),
+ 0, 0, NULL, NULL);
+
+ if (!dcookie_cache)
+ goto out;
+
+ dcookie_hashtable = kmalloc(PAGE_SIZE, GFP_KERNEL);
+ if (!dcookie_hashtable)
+ goto out_kmem;
+
+ err = 0;
+
+ /*
+ * Find the power-of-two list-heads that can fit into the allocation..
+ * We don't guarantee that "sizeof(struct list_head)" is necessarily
+ * a power-of-two.
+ */
+ hash_size = PAGE_SIZE / sizeof(struct list_head);
+ hash_bits = 0;
+ do {
+ hash_bits++;
+ } while ((hash_size >> hash_bits) != 0);
+ hash_bits--;
+
+ /*
+ * Re-calculate the actual number of entries and the mask
+ * from the number of bits we can fit.
+ */
+ hash_size = 1UL << hash_bits;
+
+ /* And initialize the newly allocated array */
+ d = dcookie_hashtable;
+ i = hash_size;
+ do {
+ INIT_LIST_HEAD(d);
+ d++;
+ i--;
+ } while (i);
+
+out:
+ return err;
+out_kmem:
+ kmem_cache_destroy(dcookie_cache);
+ goto out;
+}
+
+
+static void free_dcookie(struct dcookie_struct * dcs)
+{
+ dcs->dentry->d_cookie = NULL;
+ dput(dcs->dentry);
+ mntput(dcs->vfsmnt);
+ kmem_cache_free(dcookie_cache, dcs);
+}
+
+
+static void dcookie_exit(void)
+{
+ struct list_head * list;
+ struct list_head * pos;
+ struct list_head * pos2;
+ struct dcookie_struct * dcs;
+ size_t i;
+
+ for (i = 0; i < hash_size; ++i) {
+ list = dcookie_hashtable + i;
+ list_for_each_safe(pos, pos2, list) {
+ dcs = list_entry(pos, struct dcookie_struct, hash_list);
+ list_del(&dcs->hash_list);
+ free_dcookie(dcs);
+ }
+ }
+
+ kfree(dcookie_hashtable);
+ kmem_cache_destroy(dcookie_cache);
+}
+
+
+struct dcookie_user {
+ struct list_head next;
+};
+
+struct dcookie_user * dcookie_register(void)
+{
+ struct dcookie_user * user;
+
+ down(&dcookie_sem);
+
+ user = kmalloc(sizeof(struct dcookie_user), GFP_KERNEL);
+ if (!user)
+ goto out;
+
+ if (!is_live() && dcookie_init())
+ goto out_free;
+
+ list_add(&user->next, &dcookie_users);
+
+out:
+ up(&dcookie_sem);
+ return user;
+out_free:
+ kfree(user);
+ user = NULL;
+ goto out;
+}
+
+
+void dcookie_unregister(struct dcookie_user * user)
+{
+ down(&dcookie_sem);
+
+ list_del(&user->next);
+ kfree(user);
+
+ if (!is_live())
+ dcookie_exit();
+
+ up(&dcookie_sem);
+}
+
+EXPORT_SYMBOL_GPL(dcookie_register);
+EXPORT_SYMBOL_GPL(dcookie_unregister);
+EXPORT_SYMBOL_GPL(get_dcookie);
--- /dev/null
+/*
+ * dcookies.h
+ *
+ * Persistent cookie-path mappings
+ *
+ * Copyright 2002 John Levon <levon@movementarian.org>
+ */
+
+#ifndef DCOOKIES_H
+#define DCOOKIES_H
+
+#include <linux/config.h>
+
+#ifdef CONFIG_PROFILING
+
+#include <linux/types.h>
+
+struct dcookie_user;
+
+/**
+ * dcookie_register - register a user of dcookies
+ *
+ * Register as a dcookie user. Returns %NULL on failure.
+ */
+struct dcookie_user * dcookie_register(void);
+
+/**
+ * dcookie_unregister - unregister a user of dcookies
+ *
+ * Unregister as a dcookie user. This may invalidate
+ * any dcookie values returned from get_dcookie().
+ */
+void dcookie_unregister(struct dcookie_user * user);
+
+/**
+ * get_dcookie - acquire a dcookie
+ *
+ * Convert the given dentry/vfsmount pair into
+ * a cookie value.
+ *
+ * Returns -EINVAL if no living task has registered as a
+ * dcookie user.
+ *
+ * Returns 0 on success, with *cookie filled in
+ */
+int get_dcookie(struct dentry * dentry, struct vfsmount * vfsmnt,
+ unsigned long * cookie);
+
+#else
+
+struct dcookie_user * dcookie_register(void)
+{
+ return 0;
+}
+
+void dcookie_unregister(struct dcookie_user * user)
+{
+ return;
+}
+
+static inline int get_dcookie(struct dentry * dentry,
+ struct vfsmount * vfsmnt, unsigned long * cookie)
+{
+ return -ENOSYS;
+}
+
+#endif /* CONFIG_PROFILING */
+
+#endif /* DCOOKIES_H */
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