src/tools/memcom.rs

   1 //! Memory based communication channel between proxy & daemon for things such as cache
   2 //! invalidation.
   3
   4 use std::os::unix::io::AsRawFd;
   5 use std::sync::atomic::{AtomicUsize, Ordering};
   6 use std::sync::Arc;
   7
   8 use anyhow::Error;
   9 use nix::fcntl::OFlag;
  10 use nix::sys::mman::{MapFlags, ProtFlags};
  11 use nix::sys::stat::Mode;
  12 use once_cell::sync::OnceCell;
  13
  14 use proxmox::tools::fs::CreateOptions;
  15 use proxmox::tools::mmap::Mmap;
  16
  17 /// In-memory communication channel.
  18 pub struct Memcom {
  19     mmap: Mmap<u8>,
  20 }
  21
  22 #[repr(C)]
  23 struct Head {
  24     // User (user.cfg) cache generation/version.
  25     user_cache_generation: AtomicUsize,
  26 }
  27
  28 static INSTANCE: OnceCell<Arc<Memcom>> = OnceCell::new();
  29
  30 const MEMCOM_FILE_PATH: &str = pbs_buildcfg::rundir!("/proxmox-backup-memcom");
  31 const EMPTY_PAGE: [u8; 4096] = [0u8; 4096];
  32
  33 impl Memcom {
  34     /// Open the memory based communication channel singleton.
  35     pub fn new() -> Result<Arc<Self>, Error> {
  36         INSTANCE.get_or_try_init(Self::open).map(Arc::clone)
  37     }
  38
  39     // Actual work of `new`:
  40     fn open() -> Result<Arc<Self>, Error> {
  41         let user = pbs_config::backup_user()?;
  42         let options = CreateOptions::new()
  43             .perm(Mode::from_bits_truncate(0o660))
  44             .owner(user.uid)
  45             .group(user.gid);
  46
  47         let file = proxmox::tools::fs::atomic_open_or_create_file(
  48             MEMCOM_FILE_PATH,
  49             OFlag::O_RDWR | OFlag::O_CLOEXEC,
  50             &EMPTY_PAGE, options)?;
  51
  52         let mmap = unsafe {
  53             Mmap::<u8>::map_fd(
  54                 file.as_raw_fd(),
  55                 0,
  56                 4096,
  57                 ProtFlags::PROT_READ | ProtFlags::PROT_WRITE,
  58                 MapFlags::MAP_SHARED | MapFlags::MAP_NORESERVE | MapFlags::MAP_POPULATE,
  59             )?
  60         };
  61
  62         Ok(Arc::new(Self { mmap }))
  63     }
  64
  65     // Shortcut to get the mapped `Head` as a `Head`.
  66     fn head(&self) -> &Head {
  67         unsafe { &*(self.mmap.as_ptr() as *const u8 as *const Head) }
  68     }
  69
  70     /// Returns the user cache generation number.
  71     pub fn user_cache_generation(&self) -> usize {
  72         self.head().user_cache_generation.load(Ordering::Acquire)
  73     }
  74
  75     /// Increase the user cache generation number.
  76     pub fn increase_user_cache_generation(&self) {
  77         self.head()
  78             .user_cache_generation
  79             .fetch_add(1, Ordering::AcqRel);
  80     }
  81 }