From: Wolfgang Bumiller <w.bumiller@proxmox.com>
To: pbs-devel@lists.proxmox.com
Subject: [pbs-devel] [PATCH backup] config: don't manually track padding size
Date: Thu, 3 Mar 2022 15:00:05 +0100 [thread overview]
Message-ID: <20220303140005.167674-1-w.bumiller@proxmox.com> (raw)
make ConfigVersionCacheData a #[repr(C)] union to fix its
size and let it transparently `Deref{,Mut}` to its actual
contents
Signed-off-by: Wolfgang Bumiller <w.bumiller@proxmox.com>
---
pbs-config/src/config_version_cache.rs | 34 ++++++++++++++++++++++----
1 file changed, 29 insertions(+), 5 deletions(-)
diff --git a/pbs-config/src/config_version_cache.rs b/pbs-config/src/config_version_cache.rs
index 39a433ed..958ae457 100644
--- a/pbs-config/src/config_version_cache.rs
+++ b/pbs-config/src/config_version_cache.rs
@@ -1,7 +1,7 @@
use std::path::Path;
use std::sync::Arc;
use std::sync::atomic::{AtomicUsize, Ordering};
-use std::mem::MaybeUninit;
+use std::mem::{MaybeUninit, ManuallyDrop};
use anyhow::{bail, Error};
use once_cell::sync::OnceCell;
@@ -18,7 +18,7 @@ use proxmox_shared_memory::*;
#[derive(Debug)]
#[repr(C)]
-struct ConfigVersionCacheData {
+struct ConfigVersionCacheDataInner {
magic: [u8; 8],
// User (user.cfg) cache generation/version.
user_cache_generation: AtomicUsize,
@@ -27,11 +27,35 @@ struct ConfigVersionCacheData {
// datastore (datastore.cfg) generation/version
datastore_generation: AtomicUsize,
- // Add further atomics here (and reduce padding size)
-
- padding: [u8; 4096 - 4*8],
+ // Add further atomics here
}
+#[repr(C)]
+union ConfigVersionCacheData {
+ data: ManuallyDrop<ConfigVersionCacheDataInner>,
+ _padding: [u8; 4096],
+}
+
+#[test]
+fn assert_cache_size() {
+ assert_eq!(std::mem::size_of::<ConfigVersionCacheData>(), 4096);
+}
+
+impl std::ops::Deref for ConfigVersionCacheData {
+ type Target = ConfigVersionCacheDataInner;
+
+ #[inline]
+ fn deref(&self) -> &ConfigVersionCacheDataInner {
+ unsafe { &self.data }
+ }
+}
+
+impl std::ops::DerefMut for ConfigVersionCacheData {
+ #[inline]
+ fn deref_mut(&mut self) -> &mut ConfigVersionCacheDataInner {
+ unsafe { &mut self.data }
+ }
+}
impl Init for ConfigVersionCacheData {
fn initialize(this: &mut MaybeUninit<Self>) {
--
2.30.2
next reply other threads:[~2022-03-03 14:00 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-03-03 14:00 Wolfgang Bumiller [this message]
2022-03-10 10:15 ` [pbs-devel] applied: " Thomas Lamprecht
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