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https://gitlab.com/qemu-project/qemu
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d73415a315
clang's C11 atomic_fetch_*() functions only take a C11 atomic type
pointer argument. QEMU uses direct types (int, etc) and this causes a
compiler error when a QEMU code calls these functions in a source file
that also included <stdatomic.h> via a system header file:
$ CC=clang CXX=clang++ ./configure ... && make
../util/async.c:79:17: error: address argument to atomic operation must be a pointer to _Atomic type ('unsigned int *' invalid)
Avoid using atomic_*() names in QEMU's atomic.h since that namespace is
used by <stdatomic.h>. Prefix QEMU's APIs with 'q' so that atomic.h
and <stdatomic.h> can co-exist. I checked /usr/include on my machine and
searched GitHub for existing "qatomic_" users but there seem to be none.
This patch was generated using:
$ git grep -h -o '\<atomic\(64\)\?_[a-z0-9_]\+' include/qemu/atomic.h | \
sort -u >/tmp/changed_identifiers
$ for identifier in $(</tmp/changed_identifiers); do
sed -i "s%\<$identifier\>%q$identifier%g" \
$(git grep -I -l "\<$identifier\>")
done
I manually fixed line-wrap issues and misaligned rST tables.
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20200923105646.47864-1-stefanha@redhat.com>
137 lines
3.3 KiB
C
137 lines
3.3 KiB
C
/*
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* Atomic operations on 64-bit quantities.
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*
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* Copyright (C) 2017 Red Hat, Inc.
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*
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* Author: Paolo Bonzini <pbonzini@redhat.com>
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*
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* This work is licensed under the terms of the GNU GPL, version 2 or later.
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* See the COPYING file in the top-level directory.
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*/
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#include "qemu/osdep.h"
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#include "qemu/atomic.h"
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#include "qemu/stats64.h"
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#include "qemu/processor.h"
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#ifndef CONFIG_ATOMIC64
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static inline void stat64_rdlock(Stat64 *s)
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{
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/* Keep out incoming writers to avoid them starving us. */
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qatomic_add(&s->lock, 2);
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/* If there is a concurrent writer, wait for it. */
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while (qatomic_read(&s->lock) & 1) {
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cpu_relax();
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}
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}
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static inline void stat64_rdunlock(Stat64 *s)
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{
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qatomic_sub(&s->lock, 2);
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}
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static inline bool stat64_wrtrylock(Stat64 *s)
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{
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return qatomic_cmpxchg(&s->lock, 0, 1) == 0;
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}
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static inline void stat64_wrunlock(Stat64 *s)
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{
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qatomic_dec(&s->lock);
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}
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uint64_t stat64_get(const Stat64 *s)
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{
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uint32_t high, low;
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stat64_rdlock((Stat64 *)s);
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/* 64-bit writes always take the lock, so we can read in
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* any order.
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*/
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high = qatomic_read(&s->high);
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low = qatomic_read(&s->low);
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stat64_rdunlock((Stat64 *)s);
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return ((uint64_t)high << 32) | low;
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}
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bool stat64_add32_carry(Stat64 *s, uint32_t low, uint32_t high)
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{
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uint32_t old;
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if (!stat64_wrtrylock(s)) {
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cpu_relax();
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return false;
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}
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/* 64-bit reads always take the lock, so they don't care about the
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* order of our update. By updating s->low first, we can check
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* whether we have to carry into s->high.
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*/
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old = qatomic_fetch_add(&s->low, low);
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high += (old + low) < old;
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qatomic_add(&s->high, high);
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stat64_wrunlock(s);
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return true;
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}
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bool stat64_min_slow(Stat64 *s, uint64_t value)
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{
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uint32_t high, low;
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uint64_t orig;
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if (!stat64_wrtrylock(s)) {
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cpu_relax();
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return false;
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}
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high = qatomic_read(&s->high);
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low = qatomic_read(&s->low);
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orig = ((uint64_t)high << 32) | low;
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if (value < orig) {
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/* We have to set low before high, just like stat64_min reads
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* high before low. The value may become higher temporarily, but
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* stat64_get does not notice (it takes the lock) and the only ill
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* effect on stat64_min is that the slow path may be triggered
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* unnecessarily.
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*/
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qatomic_set(&s->low, (uint32_t)value);
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smp_wmb();
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qatomic_set(&s->high, value >> 32);
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}
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stat64_wrunlock(s);
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return true;
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}
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bool stat64_max_slow(Stat64 *s, uint64_t value)
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{
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uint32_t high, low;
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uint64_t orig;
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if (!stat64_wrtrylock(s)) {
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cpu_relax();
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return false;
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}
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high = qatomic_read(&s->high);
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low = qatomic_read(&s->low);
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orig = ((uint64_t)high << 32) | low;
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if (value > orig) {
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/* We have to set low before high, just like stat64_max reads
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* high before low. The value may become lower temporarily, but
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* stat64_get does not notice (it takes the lock) and the only ill
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* effect on stat64_max is that the slow path may be triggered
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* unnecessarily.
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*/
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qatomic_set(&s->low, (uint32_t)value);
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smp_wmb();
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qatomic_set(&s->high, value >> 32);
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}
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stat64_wrunlock(s);
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return true;
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}
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#endif
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