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annotate rust/hg-core/src/revlog/nodemap_docket.rs @ 46128:c58c8f1d63b1

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copies-rust: hide most of the comparison details inside a closure The function that compares values needs various supporting elements that are the same for each call. We are about to both make change to these element and change to call sites in our upcoming work. So abstracting most of the details will help to avoid conflict while these works happen in parallel. Differential Revision: https://phab.mercurial-scm.org/D9426
author Pierre-Yves David <pierre-yves.david@octobus.net>
date Sat, 21 Nov 2020 10:50:14 +0100
parents 9eb07ab3f2d4
children 8a4914397d02
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46091
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1 use memmap::Mmap;
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2 use std::convert::TryInto;
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3 use std::path::{Path, PathBuf};
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4
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5 use super::revlog::{mmap_open, RevlogError};
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6 use crate::utils::strip_suffix;
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7
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8 const ONDISK_VERSION: u8 = 1;
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9
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10 pub(super) struct NodeMapDocket {
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11 pub data_length: usize,
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12 // TODO: keep here more of the data from `parse()` when we need it
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13 }
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14
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15 impl NodeMapDocket {
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16 /// Return `Ok(None)` when the caller should proceed without a persistent
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17 /// nodemap:
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18 ///
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19 /// * This revlog does not have a `.n` docket file (it is not generated for
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20 /// small revlogs), or
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21 /// * The docket has an unsupported version number (repositories created by
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22 /// later hg, maybe that should be a requirement instead?), or
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23 /// * The docket file points to a missing (likely deleted) data file (this
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24 /// can happen in a rare race condition).
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25 pub fn read_from_file(
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26 index_path: &Path,
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27 ) -> Result<Option<(Self, Mmap)>, RevlogError> {
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28 let docket_path = index_path.with_extension("n");
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29 let docket_bytes = match std::fs::read(&docket_path) {
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30 Err(e) if e.kind() == std::io::ErrorKind::NotFound => {
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31 return Ok(None)
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32 }
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33 Err(e) => return Err(RevlogError::IoError(e)),
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34 Ok(bytes) => bytes,
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35 };
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36
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37 let mut input = if let Some((&ONDISK_VERSION, rest)) =
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38 docket_bytes.split_first()
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39 {
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40 rest
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41 } else {
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42 return Ok(None);
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43 };
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44 let input = &mut input;
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45
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46 let uid_size = read_u8(input)? as usize;
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47 let _tip_rev = read_be_u64(input)?;
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48 // TODO: do we care about overflow for 4 GB+ nodemap files on 32-bit
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49 // systems?
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50 let data_length = read_be_u64(input)? as usize;
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51 let _data_unused = read_be_u64(input)?;
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52 let tip_node_size = read_be_u64(input)? as usize;
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53 let uid = read_bytes(input, uid_size)?;
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54 let _tip_node = read_bytes(input, tip_node_size)?;
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55
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56 let uid =
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57 std::str::from_utf8(uid).map_err(|_| RevlogError::Corrupted)?;
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58 let docket = NodeMapDocket { data_length };
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59
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60 let data_path = rawdata_path(&docket_path, uid);
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61 // TODO: use `std::fs::read` here when the `persistent-nodemap.mmap`
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62 // config is false?
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63 match mmap_open(&data_path) {
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64 Ok(mmap) => {
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65 if mmap.len() >= data_length {
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66 Ok(Some((docket, mmap)))
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67 } else {
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68 Err(RevlogError::Corrupted)
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69 }
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70 }
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71 Err(error) => {
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72 if error.kind() == std::io::ErrorKind::NotFound {
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73 Ok(None)
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74 } else {
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75 Err(RevlogError::IoError(error))
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76 }
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77 }
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78 }
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79 }
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80 }
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81
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82 fn read_bytes<'a>(
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83 input: &mut &'a [u8],
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84 count: usize,
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85 ) -> Result<&'a [u8], RevlogError> {
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86 if let Some(start) = input.get(..count) {
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87 *input = &input[count..];
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88 Ok(start)
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89 } else {
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90 Err(RevlogError::Corrupted)
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91 }
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92 }
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93
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94 fn read_u8<'a>(input: &mut &[u8]) -> Result<u8, RevlogError> {
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95 Ok(read_bytes(input, 1)?[0])
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96 }
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97
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98 fn read_be_u64<'a>(input: &mut &[u8]) -> Result<u64, RevlogError> {
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99 let array = read_bytes(input, std::mem::size_of::<u64>())?
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100 .try_into()
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101 .unwrap();
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102 Ok(u64::from_be_bytes(array))
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103 }
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104
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105 fn rawdata_path(docket_path: &Path, uid: &str) -> PathBuf {
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106 let docket_name = docket_path
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107 .file_name()
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108 .expect("expected a base name")
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109 .to_str()
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110 .expect("expected an ASCII file name in the store");
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111 let prefix = strip_suffix(docket_name, ".n.a")
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112 .or_else(|| strip_suffix(docket_name, ".n"))
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113 .expect("expected docket path in .n or .n.a");
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114 let name = format!("{}-{}.nd", prefix, uid);
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115 docket_path
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116 .parent()
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117 .expect("expected a non-root path")
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118 .join(name)
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119 }