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annotate rust/hg-core/src/revlog/nodemap_docket.rs @ 49210:34decbaf4da3

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node: manually implement Debug I got too irritated today with the default Debug implementation of hg::revlog::Node while playing with a new parser. This isn't quite what I wanted, but it wasn't much code and it at least gives you output that's easy to visually compare to a node.hex()ed identifier from the Python side of things. Sadly, this doesn't influence the output in lldb or the VSCode debugger extension that uses lldb under the covers, but it at least means debug prints are a little more useful. Differential Revision: https://phab.mercurial-scm.org/D12608
author Augie Fackler <augie@google.com>
date Thu, 05 May 2022 14:47:26 -0400
parents 704e993e8ee9
children 048f829a445a
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1 use crate::errors::{HgError, HgResultExt};
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2 use bytes_cast::{unaligned, BytesCast};
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3 use memmap2::Mmap;
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4 use std::path::{Path, PathBuf};
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5
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6 use crate::utils::strip_suffix;
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7 use crate::vfs::Vfs;
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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 store_vfs: &Vfs,
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38 index_path: &Path,
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39 ) -> Result<Option<(Self, Mmap)>, HgError> {
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40 let docket_path = index_path.with_extension("n");
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41 let docket_bytes = if let Some(bytes) =
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42 store_vfs.read(&docket_path).io_not_found_as_none()?
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43 {
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44 bytes
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45 } else {
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46 return Ok(None);
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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 /// Treat any error as a parse error
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58 fn parse<T, E>(result: Result<T, E>) -> Result<T, HgError> {
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59 result
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60 .map_err(|_| HgError::corrupted("nodemap docket parse error"))
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61 }
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62
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63 let (header, rest) = parse(DocketHeader::from_bytes(input))?;
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64 let uid_size = header.uid_size as usize;
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65 // TODO: do we care about overflow for 4 GB+ nodemap files on 32-bit
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66 // systems?
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67 let tip_node_size = header.tip_node_size.get() as usize;
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68 let data_length = header.data_length.get() as usize;
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69 let (uid, rest) = parse(u8::slice_from_bytes(rest, uid_size))?;
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70 let (_tip_node, _rest) =
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71 parse(u8::slice_from_bytes(rest, tip_node_size))?;
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72 let uid = parse(std::str::from_utf8(uid))?;
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73 let docket = NodeMapDocket { data_length };
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74
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75 let data_path = rawdata_path(&docket_path, uid);
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76 // TODO: use `vfs.read()` here when the `persistent-nodemap.mmap`
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77 // config is false?
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78 if let Some(mmap) =
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79 store_vfs.mmap_open(&data_path).io_not_found_as_none()?
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80 {
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81 if mmap.len() >= data_length {
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82 Ok(Some((docket, mmap)))
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83 } else {
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84 Err(HgError::corrupted("persistent nodemap too short"))
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85 }
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86 } else {
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87 // Even if .hg/requires opted in, some revlogs are deemed small
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88 // enough to not need a persistent nodemap.
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89 Ok(None)
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90 }
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91 }
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92 }
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93
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94 fn rawdata_path(docket_path: &Path, uid: &str) -> PathBuf {
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95 let docket_name = docket_path
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96 .file_name()
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97 .expect("expected a base name")
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98 .to_str()
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99 .expect("expected an ASCII file name in the store");
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100 let prefix = strip_suffix(docket_name, ".n.a")
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101 .or_else(|| strip_suffix(docket_name, ".n"))
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102 .expect("expected docket path in .n or .n.a");
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103 let name = format!("{}-{}.nd", prefix, uid);
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104 docket_path
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105 .parent()
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106 .expect("expected a non-root path")
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107 .join(name)
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108 }