FreeBSD/Linux Kernel Cross Reference
sys/sys/smr_types.h

     /*-
      * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
      *
      * Copyright (c) 2019, 2020 Jeffrey Roberson <jeff@FreeBSD.org>
      *
      * Redistribution and use in source and binary forms, with or without
      * modification, are permitted provided that the following conditions
      * are met:
      * 1. Redistributions of source code must retain the above copyright
     *    notice unmodified, this list of conditions, and the following
     *    disclaimer.
     * 2. Redistributions in binary form must reproduce the above copyright
     *    notice, this list of conditions and the following disclaimer in the
     *    documentation and/or other materials provided with the distribution.
     *
     * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
     * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
     * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
     * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
     * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
     * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
     * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
     * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
     * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
     * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
     *
     * $FreeBSD$
     */
    
    #ifndef _SYS_SMR_TYPES_H_
    #define _SYS_SMR_TYPES_H_
    
    #include <sys/_smr.h>
    
    /*
     * SMR Accessors are meant to provide safe access to SMR protected
     * pointers and prevent misuse and accidental access.
     *
     * Accessors are grouped by type:
     * entered      - Use while in a read section (between smr_enter/smr_exit())
     * serialized   - Use while holding a lock that serializes writers.   Updates
     *                are synchronized with readers via included barriers.
     * unserialized - Use after the memory is out of scope and not visible to
     *                readers.
     *
     * All acceses include a parameter for an assert to verify the required
     * synchronization.  For example, a writer might use:
     *
     * smr_serialized_store(pointer, value, mtx_owned(&writelock));
     *
     * These are only enabled in INVARIANTS kernels.
     */
    
    /* Type restricting pointer access to force smr accessors. */
    #define SMR_POINTER(type)                                               \
    struct {                                                                \
            type    __ptr;          /* Do not access directly */            \
    }
    
    /*
     * Read from an SMR protected pointer while in a read section.
     */
    #define smr_entered_load(p, smr) ({                                     \
            SMR_ASSERT(SMR_ENTERED((smr)), "smr_entered_load");             \
            (__typeof((p)->__ptr))atomic_load_acq_ptr((uintptr_t *)&(p)->__ptr); \
    })
    
    /*
     * Read from an SMR protected pointer while serialized by an
     * external mechanism.  'ex' should contain an assert that the
     * external mechanism is held.  i.e. mtx_owned()
     */
    #define smr_serialized_load(p, ex) ({                                   \
            SMR_ASSERT(ex, "smr_serialized_load");                          \
            (__typeof((p)->__ptr))atomic_load_ptr(&(p)->__ptr);             \
    })
    
    /*
     * Store 'v' to an SMR protected pointer while serialized by an
     * external mechanism.  'ex' should contain an assert that the
     * external mechanism is held.  i.e. mtx_owned()
     *
     * Writers that are serialized with mutual exclusion or on a single
     * thread should use smr_serialized_store() rather than swap.
     */
    #define smr_serialized_store(p, v, ex) do {                             \
            SMR_ASSERT(ex, "smr_serialized_store");                         \
            __typeof((p)->__ptr) _v = (v);                                  \
            atomic_store_rel_ptr((uintptr_t *)&(p)->__ptr, (uintptr_t)_v);  \
    } while (0)
    
    /*
     * swap 'v' with an SMR protected pointer and return the old value
     * while serialized by an external mechanism.  'ex' should contain
     * an assert that the external mechanism is provided.  i.e. mtx_owned()
     *
     * Swap permits multiple writers to update a pointer concurrently.
     */
    #define smr_serialized_swap(p, v, ex) ({                                \
           SMR_ASSERT(ex, "smr_serialized_swap");                          \
           __typeof((p)->__ptr) _v = (v);                                  \
           /* Release barrier guarantees contents are visible to reader */ \
           atomic_thread_fence_rel();                                      \
           (__typeof((p)->__ptr))atomic_swap_ptr(                          \
               (uintptr_t *)&(p)->__ptr, (uintptr_t)_v);                   \
   })
   
   /*
    * Read from an SMR protected pointer when no serialization is required
    * such as in the destructor callback or when the caller guarantees other
    * synchronization.
    */
   #define smr_unserialized_load(p, ex) ({                                 \
           SMR_ASSERT(ex, "smr_unserialized_load");                        \
           (__typeof((p)->__ptr))atomic_load_ptr(&(p)->__ptr);             \
   })
   
   /*
    * Store to an SMR protected pointer when no serialiation is required
    * such as in the destructor callback or when the caller guarantees other
    * synchronization.
    */
   #define smr_unserialized_store(p, v, ex) do {                           \
           SMR_ASSERT(ex, "smr_unserialized_store");                       \
           __typeof((p)->__ptr) _v = (v);                                  \
           atomic_store_ptr((uintptr_t *)&(p)->__ptr, (uintptr_t)_v);      \
   } while (0)
   
   #ifndef _KERNEL
   
   /*
    * Load an SMR protected pointer when accessing kernel data structures through
    * libkvm.
    */
   #define smr_kvm_load(p) ((p)->__ptr)
   
   #endif /* !_KERNEL */
   #endif /* !_SYS_SMR_TYPES_H_ */

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