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annotate rust/hg-core/src/revlog/nodemap_docket.rs @ 46462:0800aa42bb4c

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rust: use the bytes-cast crate to parse persistent nodemaps This crate casts pointers to custom structs, with compile-time safety checks, for easy and efficient binary data parsing. See https://crates.io/crates/bytes-cast and https://docs.rs/bytes-cast/0.1.0/bytes_cast/ Differential Revision: https://phab.mercurial-scm.org/D9788
author Simon Sapin <simon.sapin@octobus.net>
date Fri, 15 Jan 2021 16:11:54 +0100
parents 8a4914397d02
children 43d63979a75e
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1 use bytes_cast::{unaligned, BytesCast};
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2 use memmap::Mmap;
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3 use std::path::{Path, PathBuf};
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4
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5 use super::revlog::RevlogError;
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6 use crate::repo::Repo;
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7 use crate::utils::strip_suffix;
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8
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9 const ONDISK_VERSION: u8 = 1;
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10
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11 pub(super) struct NodeMapDocket {
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12 pub data_length: usize,
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13 // TODO: keep here more of the data from `parse()` when we need it
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14 }
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15
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16 #[derive(BytesCast)]
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17 #[repr(C)]
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18 struct DocketHeader {
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19 uid_size: u8,
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20 _tip_rev: unaligned::U64Be,
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21 data_length: unaligned::U64Be,
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22 _data_unused: unaligned::U64Be,
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23 tip_node_size: unaligned::U64Be,
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24 }
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25
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26 impl NodeMapDocket {
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27 /// Return `Ok(None)` when the caller should proceed without a persistent
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28 /// nodemap:
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29 ///
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30 /// * This revlog does not have a `.n` docket file (it is not generated for
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31 /// small revlogs), or
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32 /// * The docket has an unsupported version number (repositories created by
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33 /// later hg, maybe that should be a requirement instead?), or
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34 /// * The docket file points to a missing (likely deleted) data file (this
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35 /// can happen in a rare race condition).
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36 pub fn read_from_file(
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37 repo: &Repo,
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38 index_path: &Path,
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39 ) -> Result<Option<(Self, Mmap)>, RevlogError> {
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40 let docket_path = index_path.with_extension("n");
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41 let docket_bytes = match repo.store_vfs().read(&docket_path) {
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42 Err(e) if e.kind() == std::io::ErrorKind::NotFound => {
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43 return Ok(None)
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44 }
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45 Err(e) => return Err(RevlogError::IoError(e)),
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46 Ok(bytes) => bytes,
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47 };
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48
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49 let input = if let Some((&ONDISK_VERSION, rest)) =
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50 docket_bytes.split_first()
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51 {
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52 rest
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53 } else {
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54 return Ok(None);
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55 };
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56
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57 let (header, rest) = DocketHeader::from_bytes(input)?;
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58 let uid_size = header.uid_size as usize;
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59 // TODO: do we care about overflow for 4 GB+ nodemap files on 32-bit
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60 // systems?
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61 let tip_node_size = header.tip_node_size.get() as usize;
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62 let data_length = header.data_length.get() as usize;
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63 let (uid, rest) = u8::slice_from_bytes(rest, uid_size)?;
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64 let (_tip_node, _rest) = u8::slice_from_bytes(rest, tip_node_size)?;
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65 let uid =
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66 std::str::from_utf8(uid).map_err(|_| RevlogError::Corrupted)?;
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67 let docket = NodeMapDocket { data_length };
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68
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69 let data_path = rawdata_path(&docket_path, uid);
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70 // TODO: use `std::fs::read` here when the `persistent-nodemap.mmap`
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71 // config is false?
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72 match repo.store_vfs().mmap_open(&data_path) {
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73 Ok(mmap) => {
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74 if mmap.len() >= data_length {
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75 Ok(Some((docket, mmap)))
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76 } else {
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77 Err(RevlogError::Corrupted)
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78 }
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79 }
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80 Err(error) => {
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81 if error.kind() == std::io::ErrorKind::NotFound {
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82 Ok(None)
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83 } else {
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84 Err(RevlogError::IoError(error))
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85 }
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86 }
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87 }
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88 }
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89 }
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90
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91 fn rawdata_path(docket_path: &Path, uid: &str) -> PathBuf {
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92 let docket_name = docket_path
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93 .file_name()
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94 .expect("expected a base name")
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95 .to_str()
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96 .expect("expected an ASCII file name in the store");
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97 let prefix = strip_suffix(docket_name, ".n.a")
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98 .or_else(|| strip_suffix(docket_name, ".n"))
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99 .expect("expected docket path in .n or .n.a");
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100 let name = format!("{}-{}.nd", prefix, uid);
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101 docket_path
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102 .parent()
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103 .expect("expected a non-root path")
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104 .join(name)
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105 }