efi: Don't use spinlocks for efi vars

All efivars operations are protected by a spinlock which prevents
interruptions and preemption. This is too restricted, we just need a
lock preventing concurrency.
The idea is to use a semaphore of count 1 and to have two ways of
locking, depending on the context:
- In interrupt context, we call down_trylock(), if it fails we return
  an error
- In normal context, we call down_interruptible()

We don't use a mutex here because the mutex_trylock() function must not
be called from interrupt context, whereas the down_trylock() can.

Signed-off-by: Sylvain Chouleur <sylvain.chouleur@intel.com>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Leif Lindholm <leif.lindholm@linaro.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Sylvain Chouleur <sylvain.chouleur@gmail.com>
Signed-off-by: Matt Fleming <matt@codeblueprint.co.uk>

6 files changed, 139 insertions, 76 deletions

diff --git a/drivers/firmware/efi/efi-pstore.c b/drivers/firmware/efi/efi-pstore.c
index 30a24d09ea6c..1c33d7469e4a 100644
--- a/drivers/firmware/efi/efi-pstore.c
+++ b/drivers/firmware/efi/efi-pstore.c
@@ -125,16 +125,19 @@ static void efi_pstore_scan_sysfs_enter(struct efivar_entry *pos,
  * @entry: deleting entry
  * @turn_off_scanning: Check if a scanning flag should be turned off
  */
-static inline void __efi_pstore_scan_sysfs_exit(struct efivar_entry *entry,
+static inline int __efi_pstore_scan_sysfs_exit(struct efivar_entry *entry,
                                                 bool turn_off_scanning)
 {
         if (entry->deleting) {
                 list_del(&entry->list);
                 efivar_entry_iter_end();
                 efivar_unregister(entry);
-                efivar_entry_iter_begin();
+                if (efivar_entry_iter_begin())
+                        return -EINTR;
         } else if (turn_off_scanning)
                 entry->scanning = false;
+
+        return 0;
 }
 
 /**
@@ -144,13 +147,18 @@ static inline void __efi_pstore_scan_sysfs_exit(struct efivar_entry *entry,
  * @head: list head
  * @stop: a flag checking if scanning will stop
  */
-static void efi_pstore_scan_sysfs_exit(struct efivar_entry *pos,
+static int efi_pstore_scan_sysfs_exit(struct efivar_entry *pos,
                                        struct efivar_entry *next,
                                        struct list_head *head, bool stop)
 {
-        __efi_pstore_scan_sysfs_exit(pos, true);
+        int ret = __efi_pstore_scan_sysfs_exit(pos, true);
+
+        if (ret)
+                return ret;
+
         if (stop)
-                __efi_pstore_scan_sysfs_exit(next, &next->list != head);
+                ret = __efi_pstore_scan_sysfs_exit(next, &next->list != head);
+        return ret;
 }
 
 /**
@@ -172,13 +180,17 @@ static int efi_pstore_sysfs_entry_iter(void *data, struct efivar_entry **pos)
         struct efivar_entry *entry, *n;
         struct list_head *head = &efivar_sysfs_list;
         int size = 0;
+        int ret;
 
         if (!*pos) {
                 list_for_each_entry_safe(entry, n, head, list) {
                         efi_pstore_scan_sysfs_enter(entry, n, head);
 
                         size = efi_pstore_read_func(entry, data);
-                        efi_pstore_scan_sysfs_exit(entry, n, head, size < 0);
+                        ret = efi_pstore_scan_sysfs_exit(entry, n, head,
+                                                         size < 0);
+                        if (ret)
+                                return ret;
                         if (size)
                                 break;
                 }
@@ -190,7 +202,9 @@ static int efi_pstore_sysfs_entry_iter(void *data, struct efivar_entry **pos)
                 efi_pstore_scan_sysfs_enter((*pos), n, head);
 
                 size = efi_pstore_read_func((*pos), data);
-                efi_pstore_scan_sysfs_exit((*pos), n, head, size < 0);
+                ret = efi_pstore_scan_sysfs_exit((*pos), n, head, size < 0);
+                if (ret)
+                        return ret;
                 if (size)
                         break;
         }
@@ -232,7 +246,10 @@ static ssize_t efi_pstore_read(u64 *id, enum pstore_type_id *type,
         if (!*data.buf)
                 return -ENOMEM;
 
-        efivar_entry_iter_begin();
+        if (efivar_entry_iter_begin()) {
+                kfree(*data.buf);
+                return -EINTR;
+        }
         size = efi_pstore_sysfs_entry_iter(&data,
                                            (struct efivar_entry **)&psi->data);
         efivar_entry_iter_end();
@@ -347,7 +364,8 @@ static int efi_pstore_erase(enum pstore_type_id type, u64 id, int count,
         edata.time = time;
         edata.name = efi_name;
 
-        efivar_entry_iter_begin();
+        if (efivar_entry_iter_begin())
+                return -EINTR;
         found = __efivar_entry_iter(efi_pstore_erase_func, &efivar_sysfs_list, &edata, &entry);
 
         if (found && !entry->scanning) {
diff --git a/drivers/firmware/efi/efivars.c b/drivers/firmware/efi/efivars.c
index 116b244dee68..3e626fd9bd4e 100644
--- a/drivers/firmware/efi/efivars.c
+++ b/drivers/firmware/efi/efivars.c
@@ -510,7 +510,8 @@ static ssize_t efivar_delete(struct file *filp, struct kobject *kobj,
                 vendor = del_var->VendorGuid;
         }
 
-        efivar_entry_iter_begin();
+        if (efivar_entry_iter_begin())
+                return -EINTR;
         entry = efivar_entry_find(name, vendor, &efivar_sysfs_list, true);
         if (!entry)
                 err = -EINVAL;
@@ -575,7 +576,10 @@ efivar_create_sysfs_entry(struct efivar_entry *new_var)
                 return ret;
 
         kobject_uevent(&new_var->kobj, KOBJ_ADD);
-        efivar_entry_add(new_var, &efivar_sysfs_list);
+        if (efivar_entry_add(new_var, &efivar_sysfs_list)) {
+                efivar_unregister(new_var);
+                return -EINTR;
+        }
 
         return 0;
 }
@@ -690,7 +694,10 @@ static int efivars_sysfs_callback(efi_char16_t *name, efi_guid_t vendor,
 
 static int efivar_sysfs_destroy(struct efivar_entry *entry, void *data)
 {
-        efivar_entry_remove(entry);
+        int err = efivar_entry_remove(entry);
+
+        if (err)
+                return err;
         efivar_unregister(entry);
         return 0;
 }
@@ -698,7 +705,14 @@ static int efivar_sysfs_destroy(struct efivar_entry *entry, void *data)
 static void efivars_sysfs_exit(void)
 {
         /* Remove all entries and destroy */
-        __efivar_entry_iter(efivar_sysfs_destroy, &efivar_sysfs_list, NULL, NULL);
+        int err;
+
+        err = __efivar_entry_iter(efivar_sysfs_destroy, &efivar_sysfs_list,
+                                  NULL, NULL);
+        if (err) {
+                pr_err("efivars: Failed to destroy sysfs entries\n");
+                return;
+        }
 
         if (efivars_new_var)
                 sysfs_remove_bin_file(&efivars_kset->kobj, efivars_new_var);
diff --git a/drivers/firmware/efi/vars.c b/drivers/firmware/efi/vars.c
index d0d807e1287e..9336ffdf6e2c 100644
--- a/drivers/firmware/efi/vars.c
+++ b/drivers/firmware/efi/vars.c
@@ -43,7 +43,7 @@ static struct efivars *__efivars;
  * 2) ->ops calls
  * 3) (un)registration of __efivars
  */
-static DEFINE_SPINLOCK(efivars_lock);
+static DEFINE_SEMAPHORE(efivars_lock);
 
 static bool efivar_wq_enabled = true;
 DECLARE_WORK(efivar_work, NULL);
@@ -442,7 +442,10 @@ int efivar_init(int (*func)(efi_char16_t *, efi_guid_t, unsigned long, void *),
                 return -ENOMEM;
         }
 
-        spin_lock_irq(&efivars_lock);
+        if (down_interruptible(&efivars_lock)) {
+                err = -EINTR;
+                goto free;
+        }
 
         /*
          * Per EFI spec, the maximum storage allocated for both
@@ -458,7 +461,7 @@ int efivar_init(int (*func)(efi_char16_t *, efi_guid_t, unsigned long, void *),
                 switch (status) {
                 case EFI_SUCCESS:
                         if (duplicates)
-                                spin_unlock_irq(&efivars_lock);
+                                up(&efivars_lock);
 
                         variable_name_size = var_name_strnsize(variable_name,
                                                                variable_name_size);
@@ -484,8 +487,12 @@ int efivar_init(int (*func)(efi_char16_t *, efi_guid_t, unsigned long, void *),
                                         status = EFI_NOT_FOUND;
                         }
 
-                        if (duplicates)
-                                spin_lock_irq(&efivars_lock);
+                        if (duplicates) {
+                                if (down_interruptible(&efivars_lock)) {
+                                        err = -EINTR;
+                                        goto free;
+                                }
+                        }
 
                         break;
                 case EFI_NOT_FOUND:
@@ -499,8 +506,8 @@ int efivar_init(int (*func)(efi_char16_t *, efi_guid_t, unsigned long, void *),
 
         } while (status != EFI_NOT_FOUND);
 
-        spin_unlock_irq(&efivars_lock);
-
+        up(&efivars_lock);
+free:
         kfree(variable_name);
 
         return err;
@@ -511,24 +518,34 @@ EXPORT_SYMBOL_GPL(efivar_init);
  * efivar_entry_add - add entry to variable list
  * @entry: entry to add to list
  * @head: list head
+ *
+ * Returns 0 on success, or a kernel error code on failure.
  */
-void efivar_entry_add(struct efivar_entry *entry, struct list_head *head)
+int efivar_entry_add(struct efivar_entry *entry, struct list_head *head)
 {
-        spin_lock_irq(&efivars_lock);
+        if (down_interruptible(&efivars_lock))
+                return -EINTR;
         list_add(&entry->list, head);
-        spin_unlock_irq(&efivars_lock);
+        up(&efivars_lock);
+
+        return 0;
 }
 EXPORT_SYMBOL_GPL(efivar_entry_add);
 
 /**
  * efivar_entry_remove - remove entry from variable list
  * @entry: entry to remove from list
+ *
+ * Returns 0 on success, or a kernel error code on failure.
  */
-void efivar_entry_remove(struct efivar_entry *entry)
+int efivar_entry_remove(struct efivar_entry *entry)
 {
-        spin_lock_irq(&efivars_lock);
+        if (down_interruptible(&efivars_lock))
+                return -EINTR;
         list_del(&entry->list);
-        spin_unlock_irq(&efivars_lock);
+        up(&efivars_lock);
+
+        return 0;
 }
 EXPORT_SYMBOL_GPL(efivar_entry_remove);
 
@@ -545,10 +562,8 @@ EXPORT_SYMBOL_GPL(efivar_entry_remove);
  */
 static void efivar_entry_list_del_unlock(struct efivar_entry *entry)
 {
-        lockdep_assert_held(&efivars_lock);
-
         list_del(&entry->list);
-        spin_unlock_irq(&efivars_lock);
+        up(&efivars_lock);
 }
 
 /**
@@ -571,8 +586,6 @@ int __efivar_entry_delete(struct efivar_entry *entry)
         const struct efivar_operations *ops = __efivars->ops;
         efi_status_t status;
 
-        lockdep_assert_held(&efivars_lock);
-
         status = ops->set_variable(entry->var.VariableName,
                                    &entry->var.VendorGuid,
                                    0, 0, NULL);
@@ -589,20 +602,22 @@ EXPORT_SYMBOL_GPL(__efivar_entry_delete);
  * variable list. It is the caller's responsibility to free @entry
  * once we return.
  *
- * Returns 0 on success, or a converted EFI status code if
- * set_variable() fails.
+ * Returns 0 on success, -EINTR if we can't grab the semaphore,
+ * converted EFI status code if set_variable() fails.
  */
 int efivar_entry_delete(struct efivar_entry *entry)
 {
         const struct efivar_operations *ops = __efivars->ops;
         efi_status_t status;
 
-        spin_lock_irq(&efivars_lock);
+        if (down_interruptible(&efivars_lock))
+                return -EINTR;
+
         status = ops->set_variable(entry->var.VariableName,
                                    &entry->var.VendorGuid,
                                    0, 0, NULL);
         if (!(status == EFI_SUCCESS || status == EFI_NOT_FOUND)) {
-                spin_unlock_irq(&efivars_lock);
+                up(&efivars_lock);
                 return efi_status_to_err(status);
         }
 
@@ -628,9 +643,9 @@ EXPORT_SYMBOL_GPL(efivar_entry_delete);
  * If @head is not NULL a lookup is performed to determine whether
  * the entry is already on the list.
  *
- * Returns 0 on success, -EEXIST if a lookup is performed and the entry
- * already exists on the list, or a converted EFI status code if
- * set_variable() fails.
+ * Returns 0 on success, -EINTR if we can't grab the semaphore,
+ * -EEXIST if a lookup is performed and the entry already exists on
+ * the list, or a converted EFI status code if set_variable() fails.
  */
 int efivar_entry_set(struct efivar_entry *entry, u32 attributes,
                      unsigned long size, void *data, struct list_head *head)
@@ -640,10 +655,10 @@ int efivar_entry_set(struct efivar_entry *entry, u32 attributes,
         efi_char16_t *name = entry->var.VariableName;
         efi_guid_t vendor = entry->var.VendorGuid;
 
-        spin_lock_irq(&efivars_lock);
-
+        if (down_interruptible(&efivars_lock))
+                return -EINTR;
         if (head && efivar_entry_find(name, vendor, head, false)) {
-                spin_unlock_irq(&efivars_lock);
+                up(&efivars_lock);
                 return -EEXIST;
         }
 
@@ -652,7 +667,7 @@ int efivar_entry_set(struct efivar_entry *entry, u32 attributes,
                 status = ops->set_variable(name, &vendor,
                                            attributes, size, data);
 
-        spin_unlock_irq(&efivars_lock);
+        up(&efivars_lock);
 
         return efi_status_to_err(status);
 
@@ -673,23 +688,22 @@ efivar_entry_set_nonblocking(efi_char16_t *name, efi_guid_t vendor,
                              u32 attributes, unsigned long size, void *data)
 {
         const struct efivar_operations *ops = __efivars->ops;
-        unsigned long flags;
         efi_status_t status;
 
-        if (!spin_trylock_irqsave(&efivars_lock, flags))
+        if (down_trylock(&efivars_lock))
                 return -EBUSY;
 
         status = check_var_size_nonblocking(attributes,
                                             size + ucs2_strsize(name, 1024));
         if (status != EFI_SUCCESS) {
-                spin_unlock_irqrestore(&efivars_lock, flags);
+                up(&efivars_lock);
                 return -ENOSPC;
         }
 
         status = ops->set_variable_nonblocking(name, &vendor, attributes,
                                                size, data);
 
-        spin_unlock_irqrestore(&efivars_lock, flags);
+        up(&efivars_lock);
         return efi_status_to_err(status);
 }
 
@@ -714,7 +728,6 @@ int efivar_entry_set_safe(efi_char16_t *name, efi_guid_t vendor, u32 attributes,
                           bool block, unsigned long size, void *data)
 {
         const struct efivar_operations *ops = __efivars->ops;
-        unsigned long flags;
         efi_status_t status;
 
         if (!ops->query_variable_store)
@@ -735,21 +748,22 @@ int efivar_entry_set_safe(efi_char16_t *name, efi_guid_t vendor, u32 attributes,
                                                     size, data);
 
         if (!block) {
-                if (!spin_trylock_irqsave(&efivars_lock, flags))
+                if (down_trylock(&efivars_lock))
                         return -EBUSY;
         } else {
-                spin_lock_irqsave(&efivars_lock, flags);
+                if (down_interruptible(&efivars_lock))
+                        return -EINTR;
         }
 
         status = check_var_size(attributes, size + ucs2_strsize(name, 1024));
         if (status != EFI_SUCCESS) {
-                spin_unlock_irqrestore(&efivars_lock, flags);
+                up(&efivars_lock);
                 return -ENOSPC;
         }
 
         status = ops->set_variable(name, &vendor, attributes, size, data);
 
-        spin_unlock_irqrestore(&efivars_lock, flags);
+        up(&efivars_lock);
 
         return efi_status_to_err(status);
 }
@@ -779,8 +793,6 @@ struct efivar_entry *efivar_entry_find(efi_char16_t *name, efi_guid_t guid,
         int strsize1, strsize2;
         bool found = false;
 
-        lockdep_assert_held(&efivars_lock);
-
         list_for_each_entry_safe(entry, n, head, list) {
                 strsize1 = ucs2_strsize(name, 1024);
                 strsize2 = ucs2_strsize(entry->var.VariableName, 1024);
@@ -822,10 +834,11 @@ int efivar_entry_size(struct efivar_entry *entry, unsigned long *size)
 
         *size = 0;
 
-        spin_lock_irq(&efivars_lock);
+        if (down_interruptible(&efivars_lock))
+                return -EINTR;
         status = ops->get_variable(entry->var.VariableName,
                                    &entry->var.VendorGuid, NULL, size, NULL);
-        spin_unlock_irq(&efivars_lock);
+        up(&efivars_lock);
 
         if (status != EFI_BUFFER_TOO_SMALL)
                 return efi_status_to_err(status);
@@ -851,8 +864,6 @@ int __efivar_entry_get(struct efivar_entry *entry, u32 *attributes,
         const struct efivar_operations *ops = __efivars->ops;
         efi_status_t status;
 
-        lockdep_assert_held(&efivars_lock);
-
         status = ops->get_variable(entry->var.VariableName,
                                    &entry->var.VendorGuid,
                                    attributes, size, data);
@@ -874,11 +885,12 @@ int efivar_entry_get(struct efivar_entry *entry, u32 *attributes,
         const struct efivar_operations *ops = __efivars->ops;
         efi_status_t status;
 
-        spin_lock_irq(&efivars_lock);
+        if (down_interruptible(&efivars_lock))
+                return -EINTR;
         status = ops->get_variable(entry->var.VariableName,
                                    &entry->var.VendorGuid,
                                    attributes, size, data);
-        spin_unlock_irq(&efivars_lock);
+        up(&efivars_lock);
 
         return efi_status_to_err(status);
 }
@@ -925,7 +937,8 @@ int efivar_entry_set_get_size(struct efivar_entry *entry, u32 attributes,
          * set_variable call, and removal of the variable from the efivars
          * list (in the case of an authenticated delete).
          */
-        spin_lock_irq(&efivars_lock);
+        if (down_interruptible(&efivars_lock))
+                return -EINTR;
 
         /*
          * Ensure that the available space hasn't shrunk below the safe level
@@ -965,7 +978,7 @@ int efivar_entry_set_get_size(struct efivar_entry *entry, u32 attributes,
         if (status == EFI_NOT_FOUND)
                 efivar_entry_list_del_unlock(entry);
         else
-                spin_unlock_irq(&efivars_lock);
+                up(&efivars_lock);
 
         if (status && status != EFI_BUFFER_TOO_SMALL)
                 return efi_status_to_err(status);
@@ -973,7 +986,7 @@ int efivar_entry_set_get_size(struct efivar_entry *entry, u32 attributes,
         return 0;
 
 out:
-        spin_unlock_irq(&efivars_lock);
+        up(&efivars_lock);
         return err;
 
 }
@@ -986,9 +999,9 @@ EXPORT_SYMBOL_GPL(efivar_entry_set_get_size);
  * efivar_entry_iter_end() is called. This function is usually used in
  * conjunction with __efivar_entry_iter() or efivar_entry_iter().
  */
-void efivar_entry_iter_begin(void)
+int efivar_entry_iter_begin(void)
 {
-        spin_lock_irq(&efivars_lock);
+        return down_interruptible(&efivars_lock);
 }
 EXPORT_SYMBOL_GPL(efivar_entry_iter_begin);
 
@@ -999,7 +1012,7 @@ EXPORT_SYMBOL_GPL(efivar_entry_iter_begin);
  */
 void efivar_entry_iter_end(void)
 {
-        spin_unlock_irq(&efivars_lock);
+        up(&efivars_lock);
 }
 EXPORT_SYMBOL_GPL(efivar_entry_iter_end);
 
@@ -1075,7 +1088,9 @@ int efivar_entry_iter(int (*func)(struct efivar_entry *, void *),
 {
         int err = 0;
 
-        efivar_entry_iter_begin();
+        err = efivar_entry_iter_begin();
+        if (err)
+                return err;
         err = __efivar_entry_iter(func, head, data, NULL);
         efivar_entry_iter_end();
 
@@ -1120,12 +1135,17 @@ int efivars_register(struct efivars *efivars,
                      const struct efivar_operations *ops,
                      struct kobject *kobject)
 {
-        spin_lock_irq(&efivars_lock);
+        if (down_interruptible(&efivars_lock))
+                return -EINTR;
+
         efivars->ops = ops;
         efivars->kobject = kobject;
 
         __efivars = efivars;
-        spin_unlock_irq(&efivars_lock);
+
+        pr_info("Registered efivars operations\n");
+
+        up(&efivars_lock);
 
         return 0;
 }
@@ -1142,7 +1162,9 @@ int efivars_unregister(struct efivars *efivars)
 {
         int rv;
 
-        spin_lock_irq(&efivars_lock);
+        if (down_interruptible(&efivars_lock))
+                return -EINTR;
+
         if (!__efivars) {
                 printk(KERN_ERR "efivars not registered\n");
                 rv = -EINVAL;
@@ -1154,11 +1176,12 @@ int efivars_unregister(struct efivars *efivars)
                 goto out;
         }
 
+        pr_info("Unregistered efivars operations\n");
         __efivars = NULL;
 
         rv = 0;
 out:
-        spin_unlock_irq(&efivars_lock);
+        up(&efivars_lock);
         return rv;
 }
 EXPORT_SYMBOL_GPL(efivars_unregister);
diff --git a/fs/efivarfs/inode.c b/fs/efivarfs/inode.c
index 1d73fc6dba13..cbb50cadcffc 100644
--- a/fs/efivarfs/inode.c
+++ b/fs/efivarfs/inode.c
@@ -105,7 +105,10 @@ static int efivarfs_create(struct inode *dir, struct dentry *dentry,
 
         inode->i_private = var;
 
-        efivar_entry_add(var, &efivarfs_list);
+        err = efivar_entry_add(var, &efivarfs_list);
+        if (err)
+                goto out;
+
         d_instantiate(dentry, inode);
         dget(dentry);
 out:
diff --git a/fs/efivarfs/super.c b/fs/efivarfs/super.c
index 688ccc16b702..01e3d6e53944 100644
--- a/fs/efivarfs/super.c
+++ b/fs/efivarfs/super.c
@@ -161,7 +161,9 @@ static int efivarfs_callback(efi_char16_t *name16, efi_guid_t vendor,
         kfree(name);
 
         efivar_entry_size(entry, &size);
-        efivar_entry_add(entry, &efivarfs_list);
+        err = efivar_entry_add(entry, &efivarfs_list);
+        if (err)
+                goto fail_inode;
 
         inode_lock(inode);
         inode->i_private = entry;
@@ -182,7 +184,10 @@ fail:
 
 static int efivarfs_destroy(struct efivar_entry *entry, void *data)
 {
-        efivar_entry_remove(entry);
+        int err = efivar_entry_remove(entry);
+
+        if (err)
+                return err;
         kfree(entry);
         return 0;
 }
diff --git a/include/linux/efi.h b/include/linux/efi.h
index deecb2902715..4d6da7b66c19 100644
--- a/include/linux/efi.h
+++ b/include/linux/efi.h
@@ -1297,8 +1297,8 @@ struct kobject *efivars_kobject(void);
 int efivar_init(int (*func)(efi_char16_t *, efi_guid_t, unsigned long, void *),
                 void *data, bool duplicates, struct list_head *head);
 
-void efivar_entry_add(struct efivar_entry *entry, struct list_head *head);
-void efivar_entry_remove(struct efivar_entry *entry);
+int efivar_entry_add(struct efivar_entry *entry, struct list_head *head);
+int efivar_entry_remove(struct efivar_entry *entry);
 
 int __efivar_entry_delete(struct efivar_entry *entry);
 int efivar_entry_delete(struct efivar_entry *entry);
@@ -1315,7 +1315,7 @@ int efivar_entry_set_get_size(struct efivar_entry *entry, u32 attributes,
 int efivar_entry_set_safe(efi_char16_t *name, efi_guid_t vendor, u32 attributes,
                           bool block, unsigned long size, void *data);
 
-void efivar_entry_iter_begin(void);
+int efivar_entry_iter_begin(void);
 void efivar_entry_iter_end(void);
 
 int __efivar_entry_iter(int (*func)(struct efivar_entry *, void *),