-//! This mudule implements the proxmox backup chunked data storage
+//! This module implements the data storage and access layer.
+//!
+//! # Data formats
+//!
+//! PBS splits large files into chunks, and stores them deduplicated using
+//! a content addressable storage format.
+//!
+//! Backup snapshots are stored as folders containing a manifest file and
+//! potentially one or more index or blob files.
+//!
+//! The manifest contains hashes of all other files and can be signed by
+//! the client.
+//!
+//! Blob files contain data directly. They are used for config files and
+//! the like.
+//!
+//! Index files are used to reconstruct an original file. They contain a
+//! list of SHA256 checksums. The `DynamicIndex*` format is able to deal
+//! with dynamic chunk sizes (CT and host backups), whereas the
+//! `FixedIndex*` format is an optimization to store a list of equal sized
+//! chunks (VMs, whole block devices).
+//!
+//! A chunk is defined as a binary blob, which is stored inside a
+//! [ChunkStore](struct.ChunkStore.html) instead of the backup directory
+//! directly, and can be addressed by its SHA256 digest.
+//!
+//!
+//! # Garbage Collection (GC)
+//!
+//! Deleting backups is as easy as deleting the corresponding .idx files.
+//! However, this does not free up any storage, because those files just
+//! contain references to chunks.
+//!
+//! To free up some storage, we run a garbage collection process at
+//! regular intervals. The collector uses a mark and sweep approach. In
+//! the first phase, it scans all .idx files to mark used chunks. The
+//! second phase then removes all unmarked chunks from the store.
+//!
+//! The locking mechanisms mentioned below make sure that we are the only
+//! process running GC. We still want to be able to create backups during
+//! GC, so there may be multiple backup threads/tasks running, either
+//! started before GC, or while GC is running.
+//!
+//! ## `atime` based GC
+//!
+//! The idea here is to mark chunks by updating the `atime` (access
+//! timestamp) on the chunk file. This is quite simple and does not need
+//! additional RAM.
+//!
+//! One minor problem is that recent Linux versions use the `relatime`
+//! mount flag by default for performance reasons (and we want that). When
+//! enabled, `atime` data is written to the disk only if the file has been
+//! modified since the `atime` data was last updated (`mtime`), or if the
+//! file was last accessed more than a certain amount of time ago (by
+//! default 24h). So we may only delete chunks with `atime` older than 24
+//! hours.
+//!
+//! Another problem arises from running backups. The mark phase does not
+//! find any chunks from those backups, because there is no .idx file for
+//! them (created after the backup). Chunks created or touched by those
+//! backups may have an `atime` as old as the start time of those backups.
+//! Please note that the backup start time may predate the GC start time.
+//! So we may only delete chunks older than the start time of those
+//! running backup jobs, which might be more than 24h back (this is the
+//! reason why ProcessLocker exclusive locks only have to be exclusive
+//! between processes, since within one we can determine the age of the
+//! oldest shared lock).
+//!
+//! ## Store `marks` in RAM using a HASH
+//!
+//! Might be better. Under investigation.
+//!
+//!
+//! # Locking
+//!
+//! Since PBS allows multiple potentially interfering operations at the
+//! same time (e.g. garbage collect, prune, multiple backup creations
+//! (only in seperate groups), forget, ...), these need to lock against
+//! each other in certain scenarios. There is no overarching global lock
+//! though, instead always the finest grained lock possible is used,
+//! because running these operations concurrently is treated as a feature
+//! on its own.
+//!
+//! ## Inter-process Locking
+//!
+//! We need to be able to restart the proxmox-backup service daemons, so
+//! that we can update the software without rebooting the host. But such
+//! restarts must not abort running backup jobs, so we need to keep the
+//! old service running until those jobs are finished. This implies that
+//! we need some kind of locking for modifying chunks and indices in the
+//! ChunkStore.
+//!
+//! Please note that it is perfectly valid to have multiple
+//! parallel ChunkStore writers, even when they write the same chunk
+//! (because the chunk would have the same name and the same data, and
+//! writes are completed atomically via a rename). The only problem is
+//! garbage collection, because we need to avoid deleting chunks which are
+//! still referenced.
+//!
+//! To do this we use the
+//! [ProcessLocker](../tools/struct.ProcessLocker.html).
+//!
+//! ### ChunkStore-wide
+//!
+//! * Create Index Files:
+//!
+//! Acquire shared lock for ChunkStore.
+//!
+//! Note: When creating .idx files, we create a temporary .tmp file,
+//! then do an atomic rename.
+//!
+//! * Garbage Collect:
+//!
+//! Acquire exclusive lock for ChunkStore. If we have
+//! already a shared lock for the ChunkStore, try to upgrade that
+//! lock.
+//!
+//! Exclusive locks only work _between processes_. It is valid to have an
+//! exclusive and one or more shared locks held within one process. Writing
+//! chunks within one process is synchronized using the gc_mutex.
+//!
+//! On server restart, we stop any running GC in the old process to avoid
+//! having the exclusive lock held for too long.
+//!
+//! ## Locking table
+//!
+//! Below table shows all operations that play a role in locking, and which
+//! mechanisms are used to make their concurrent usage safe.
+//!
+//! | starting ><br>v during | read index file | create index file | GC mark | GC sweep | update manifest | forget | prune | create backup | verify | reader api |
+//! |-|-|-|-|-|-|-|-|-|-|-|
+//! | **read index file** | / | / | / | / | / | mmap stays valid, oldest_shared_lock prevents GC | see forget column | / | / | / |
+//! | **create index file** | / | / | / | / | / | / | / | /, happens at the end, after all chunks are touched | /, only happens without a manifest | / |
+//! | **GC mark** | / | Datastore process-lock shared | gc_mutex, exclusive ProcessLocker | gc_mutex | /, GC only cares about index files, not manifests | tells GC about removed chunks | see forget column | /, index files don’t exist yet | / | / |
+//! | **GC sweep** | / | Datastore process-lock shared | gc_mutex, exclusive ProcessLocker | gc_mutex | / | /, chunks already marked | see forget column | chunks get touched; chunk_store.mutex; oldest PL lock | / | / |
+//! | **update manifest** | / | / | / | / | update_manifest lock | update_manifest lock, remove dir under lock | see forget column | /, “write manifest” happens at the end | /, can call “write manifest”, see that column | / |
+//! | **forget** | / | / | removed_during_gc mutex is held during unlink | marking done, doesn’t matter if forgotten now | update_manifest lock, forget waits for lock | /, unlink is atomic | causes forget to fail, but that’s OK | running backup has snapshot flock | /, potentially detects missing folder | shared snap flock |
+//! | **prune** | / | / | see forget row | see forget row | see forget row | causes warn in prune, but no error | see forget column | running and last non-running can’t be pruned | see forget row | shared snap flock |
+//! | **create backup** | / | only time this happens, thus has snapshot flock | / | chunks get touched; chunk_store.mutex; oldest PL lock | no lock, but cannot exist beforehand | snapshot flock, can’t be forgotten | running and last non-running can’t be pruned | snapshot group flock, only one running per group | /, won’t be verified since manifest missing | / |
+//! | **verify** | / | / | / | / | see “update manifest” row | /, potentially detects missing folder | see forget column | / | /, but useless (“update manifest” protects itself) | / |
+//! | **reader api** | / | / | / | /, open snap can’t be forgotten, so ref must exist | / | prevented by shared snap flock | prevented by shared snap flock | / | / | /, lock is shared |!
+//! * / = no interaction
+//! * shared/exclusive from POV of 'starting' process
-pub mod chunker;
-pub mod chunk_store;
-pub mod image_index;
-pub mod datastore;
+use anyhow::{bail, Error};
+
+// Note: .pcat1 => Proxmox Catalog Format version 1
+pub const CATALOG_NAME: &str = "catalog.pcat1.didx";
+
+#[macro_export]
+macro_rules! PROXMOX_BACKUP_PROTOCOL_ID_V1 {
+ () => { "proxmox-backup-protocol-v1" }
+}
+
+#[macro_export]
+macro_rules! PROXMOX_BACKUP_READER_PROTOCOL_ID_V1 {
+ () => { "proxmox-backup-reader-protocol-v1" }
+}
+
+/// Unix system user used by proxmox-backup-proxy
+pub const BACKUP_USER_NAME: &str = "backup";
+/// Unix system group used by proxmox-backup-proxy
+pub const BACKUP_GROUP_NAME: &str = "backup";
+
+/// Return User info for the 'backup' user (``getpwnam_r(3)``)
+pub fn backup_user() -> Result<nix::unistd::User, Error> {
+ match nix::unistd::User::from_name(BACKUP_USER_NAME)? {
+ Some(user) => Ok(user),
+ None => bail!("Unable to lookup backup user."),
+ }
+}
+
+/// Return Group info for the 'backup' group (``getgrnam(3)``)
+pub fn backup_group() -> Result<nix::unistd::Group, Error> {
+ match nix::unistd::Group::from_name(BACKUP_GROUP_NAME)? {
+ Some(group) => Ok(group),
+ None => bail!("Unable to lookup backup user."),
+ }
+}
+
+mod file_formats;
+pub use file_formats::*;
+
+mod manifest;
+pub use manifest::*;
+
+mod crypt_config;
+pub use crypt_config::*;
+
+mod key_derivation;
+pub use key_derivation::*;
+
+mod crypt_reader;
+pub use crypt_reader::*;
+
+mod crypt_writer;
+pub use crypt_writer::*;
+
+mod checksum_reader;
+pub use checksum_reader::*;
+
+mod checksum_writer;
+pub use checksum_writer::*;
+
+mod chunker;
+pub use chunker::*;
+
+mod data_blob;
+pub use data_blob::*;
+
+mod data_blob_reader;
+pub use data_blob_reader::*;
+
+mod data_blob_writer;
+pub use data_blob_writer::*;
+
+mod catalog;
+pub use catalog::*;
+
+mod chunk_stream;
+pub use chunk_stream::*;
+
+mod chunk_stat;
+pub use chunk_stat::*;
+
+mod read_chunk;
+pub use read_chunk::*;
+
+mod chunk_store;
+pub use chunk_store::*;
+
+mod index;
+pub use index::*;
+
+mod fixed_index;
+pub use fixed_index::*;
+
+mod dynamic_index;
+pub use dynamic_index::*;
+
+mod backup_info;
+pub use backup_info::*;
+
+mod prune;
+pub use prune::*;
+
+mod datastore;
+pub use datastore::*;
+
+mod verify;
+pub use verify::*;
+
+mod catalog_shell;
+pub use catalog_shell::*;
+
+mod async_index_reader;
+pub use async_index_reader::*;
projects / proxmox-backup.git / blobdiff