[pbs-devel] [PATCH v2 proxmox-backup 2/4] datastore: add manifest locking
Stefan Reiter
s.reiter at proxmox.com
Thu Oct 15 12:49:14 CEST 2020
Avoid races when updating manifest data by flocking a lock file.
update_manifest is used to ensure updates always happen with the lock
held.
Snapshot deletion also acquires the lock, so it cannot interfere with an
outstanding manifest write.
Signed-off-by: Stefan Reiter <s.reiter at proxmox.com>
---
v2:
* Use seperate manifest lock file
* Change store_manifest to update_manifest to force consumers to use correct
locking
* Don't hold lock across verify, reload manifest at the end
* Update comments
src/api2/admin/datastore.rs | 8 +++----
src/api2/backup/environment.rs | 13 ++++------
src/backup/datastore.rs | 43 +++++++++++++++++++++++++++++-----
src/backup/manifest.rs | 1 +
src/backup/verify.rs | 9 +++----
5 files changed, 50 insertions(+), 24 deletions(-)
diff --git a/src/api2/admin/datastore.rs b/src/api2/admin/datastore.rs
index de39cd1b..4f15c1cd 100644
--- a/src/api2/admin/datastore.rs
+++ b/src/api2/admin/datastore.rs
@@ -1481,11 +1481,9 @@ fn set_notes(
let allowed = (user_privs & PRIV_DATASTORE_READ) != 0;
if !allowed { check_backup_owner(&datastore, backup_dir.group(), &userid)?; }
- let (mut manifest, _) = datastore.load_manifest(&backup_dir)?;
-
- manifest.unprotected["notes"] = notes.into();
-
- datastore.store_manifest(&backup_dir, manifest)?;
+ datastore.update_manifest(&backup_dir,|manifest| {
+ manifest.unprotected["notes"] = notes.into();
+ }).map_err(|err| format_err!("unable to update manifest blob - {}", err))?;
Ok(())
}
diff --git a/src/api2/backup/environment.rs b/src/api2/backup/environment.rs
index f00c2cd3..c4f166df 100644
--- a/src/api2/backup/environment.rs
+++ b/src/api2/backup/environment.rs
@@ -472,16 +472,11 @@ impl BackupEnvironment {
bail!("backup does not contain valid files (file count == 0)");
}
- // check manifest
- let (mut manifest, _) = self.datastore.load_manifest(&self.backup_dir)
- .map_err(|err| format_err!("unable to load manifest blob - {}", err))?;
-
+ // check for valid manifest and store stats
let stats = serde_json::to_value(state.backup_stat)?;
-
- manifest.unprotected["chunk_upload_stats"] = stats;
-
- self.datastore.store_manifest(&self.backup_dir, manifest)
- .map_err(|err| format_err!("unable to store manifest blob - {}", err))?;
+ self.datastore.update_manifest(&self.backup_dir, |manifest| {
+ manifest.unprotected["chunk_upload_stats"] = stats;
+ }).map_err(|err| format_err!("unable to update manifest blob - {}", err))?;
if let Some(base) = &self.last_backup {
let path = self.datastore.snapshot_path(&base.backup_dir);
diff --git a/src/backup/datastore.rs b/src/backup/datastore.rs
index ca8ca438..7b2bee7e 100644
--- a/src/backup/datastore.rs
+++ b/src/backup/datastore.rs
@@ -3,17 +3,19 @@ use std::io::{self, Write};
use std::path::{Path, PathBuf};
use std::sync::{Arc, Mutex};
use std::convert::TryFrom;
+use std::time::Duration;
+use std::fs::File;
use anyhow::{bail, format_err, Error};
use lazy_static::lazy_static;
-use proxmox::tools::fs::{replace_file, CreateOptions};
+use proxmox::tools::fs::{replace_file, CreateOptions, open_file_locked};
use super::backup_info::{BackupGroup, BackupDir};
use super::chunk_store::ChunkStore;
use super::dynamic_index::{DynamicIndexReader, DynamicIndexWriter};
use super::fixed_index::{FixedIndexReader, FixedIndexWriter};
-use super::manifest::{MANIFEST_BLOB_NAME, CLIENT_LOG_BLOB_NAME, BackupManifest};
+use super::manifest::{MANIFEST_BLOB_NAME, MANIFEST_LOCK_NAME, CLIENT_LOG_BLOB_NAME, BackupManifest};
use super::index::*;
use super::{DataBlob, ArchiveType, archive_type};
use crate::config::datastore;
@@ -235,9 +237,10 @@ impl DataStore {
let full_path = self.snapshot_path(backup_dir);
- let _guard;
+ let (_guard, _manifest_guard);
if !force {
_guard = lock_dir_noblock(&full_path, "snapshot", "possibly running or in use")?;
+ _manifest_guard = self.lock_manifest(backup_dir);
}
// Acquire lock and keep it during remove operation, so there's no
@@ -665,8 +668,27 @@ impl DataStore {
digest_str,
err,
))
- }
+ }
+ fn lock_manifest(
+ &self,
+ backup_dir: &BackupDir,
+ ) -> Result<File, Error> {
+ let mut path = self.base_path();
+ path.push(backup_dir.relative_path());
+ path.push(&MANIFEST_LOCK_NAME);
+
+ // update_manifest should never take a long time, so if someone else has
+ // the lock we can simply block a bit and should get it soon
+ open_file_locked(&path, Duration::from_secs(5), true)
+ .map_err(|err| {
+ format_err!(
+ "unable to acquire manifest lock {:?} - {}", &path, err
+ )
+ })
+ }
+
+ /// Load the manifest without a lock. Must not be written back.
pub fn load_manifest(
&self,
backup_dir: &BackupDir,
@@ -677,11 +699,19 @@ impl DataStore {
Ok((manifest, raw_size))
}
- pub fn store_manifest(
+ /// Update the manifest of the specified snapshot. Never write a manifest directly,
+ /// only use this method - anything else may break locking guarantees.
+ pub fn update_manifest(
&self,
backup_dir: &BackupDir,
- manifest: BackupManifest,
+ update_fn: impl FnOnce(&mut BackupManifest),
) -> Result<(), Error> {
+
+ let _guard = self.lock_manifest(backup_dir)?;
+ let (mut manifest, _) = self.load_manifest(&backup_dir)?;
+
+ update_fn(&mut manifest);
+
let manifest = serde_json::to_value(manifest)?;
let manifest = serde_json::to_string_pretty(&manifest)?;
let blob = DataBlob::encode(manifest.as_bytes(), None, true)?;
@@ -691,6 +721,7 @@ impl DataStore {
path.push(backup_dir.relative_path());
path.push(MANIFEST_BLOB_NAME);
+ // atomic replace invalidates flock - no other writes past this point!
replace_file(&path, raw_data, CreateOptions::new())?;
Ok(())
diff --git a/src/backup/manifest.rs b/src/backup/manifest.rs
index 609cc998..51980a07 100644
--- a/src/backup/manifest.rs
+++ b/src/backup/manifest.rs
@@ -8,6 +8,7 @@ use ::serde::{Deserialize, Serialize};
use crate::backup::{BackupDir, CryptMode, CryptConfig};
pub const MANIFEST_BLOB_NAME: &str = "index.json.blob";
+pub const MANIFEST_LOCK_NAME: &str = ".index.json.lck";
pub const CLIENT_LOG_BLOB_NAME: &str = "client.log.blob";
mod hex_csum {
diff --git a/src/backup/verify.rs b/src/backup/verify.rs
index 05b6ba86..ea3fa760 100644
--- a/src/backup/verify.rs
+++ b/src/backup/verify.rs
@@ -300,7 +300,7 @@ pub fn verify_backup_dir(
return Ok(true);
}
- let mut manifest = match datastore.load_manifest(&backup_dir) {
+ let manifest = match datastore.load_manifest(&backup_dir) {
Ok((manifest, _)) => manifest,
Err(err) => {
task_log!(
@@ -367,9 +367,10 @@ pub fn verify_backup_dir(
state: verify_result,
upid,
};
- manifest.unprotected["verify_state"] = serde_json::to_value(verify_state)?;
- datastore.store_manifest(&backup_dir, manifest)
- .map_err(|err| format_err!("unable to store manifest blob - {}", err))?;
+ let verify_state = serde_json::to_value(verify_state)?;
+ datastore.update_manifest(&backup_dir, |manifest| {
+ manifest.unprotected["verify_state"] = verify_state;
+ }).map_err(|err| format_err!("unable to update manifest blob - {}", err))?;
Ok(error_count == 0)
}
--
2.20.1
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