compiler/rustc_metadata/src/fs.rs

   1 use crate::errors::{
   2     FailedCreateEncodedMetadata, FailedCreateFile, FailedCreateTempdir, FailedWriteError,
   3 };
   4 use crate::{encode_metadata, EncodedMetadata};
   5
   6 use rustc_data_structures::temp_dir::MaybeTempDir;
   7 use rustc_hir::def_id::LOCAL_CRATE;
   8 use rustc_middle::ty::TyCtxt;
   9 use rustc_session::config::{CrateType, OutputType};
  10 use rustc_session::output::filename_for_metadata;
  11 use rustc_session::Session;
  12 use tempfile::Builder as TempFileBuilder;
  13
  14 use std::fs;
  15 use std::path::{Path, PathBuf};
  16
  17 // FIXME(eddyb) maybe include the crate name in this?
  18 pub const METADATA_FILENAME: &str = "lib.rmeta";
  19
  20 /// We use a temp directory here to avoid races between concurrent rustc processes,
  21 /// such as builds in the same directory using the same filename for metadata while
  22 /// building an `.rlib` (stomping over one another), or writing an `.rmeta` into a
  23 /// directory being searched for `extern crate` (observing an incomplete file).
  24 /// The returned path is the temporary file containing the complete metadata.
  25 pub fn emit_wrapper_file(
  26     sess: &Session,
  27     data: &[u8],
  28     tmpdir: &MaybeTempDir,
  29     name: &str,
  30 ) -> PathBuf {
  31     let out_filename = tmpdir.as_ref().join(name);
  32     let result = fs::write(&out_filename, data);
  33
  34     if let Err(err) = result {
  35         sess.emit_fatal(FailedWriteError { filename: out_filename, err });
  36     }
  37
  38     out_filename
  39 }
  40
  41 pub fn encode_and_write_metadata(tcx: TyCtxt<'_>) -> (EncodedMetadata, bool) {
  42     #[derive(PartialEq, Eq, PartialOrd, Ord)]
  43     enum MetadataKind {
  44         None,
  45         Uncompressed,
  46         Compressed,
  47     }
  48
  49     let metadata_kind = tcx
  50         .sess
  51         .crate_types()
  52         .iter()
  53         .map(|ty| match *ty {
  54             CrateType::Executable | CrateType::Staticlib | CrateType::Cdylib => MetadataKind::None,
  55
  56             CrateType::Rlib => MetadataKind::Uncompressed,
  57
  58             CrateType::Dylib | CrateType::ProcMacro => MetadataKind::Compressed,
  59         })
  60         .max()
  61         .unwrap_or(MetadataKind::None);
  62
  63     let crate_name = tcx.crate_name(LOCAL_CRATE);
  64     let out_filename = filename_for_metadata(tcx.sess, crate_name, tcx.output_filenames(()));
  65     // To avoid races with another rustc process scanning the output directory,
  66     // we need to write the file somewhere else and atomically move it to its
  67     // final destination, with an `fs::rename` call. In order for the rename to
  68     // always succeed, the temporary file needs to be on the same filesystem,
  69     // which is why we create it inside the output directory specifically.
  70     let metadata_tmpdir = TempFileBuilder::new()
  71         .prefix("rmeta")
  72         .tempdir_in(out_filename.parent().unwrap_or_else(|| Path::new("")))
  73         .unwrap_or_else(|err| tcx.sess.emit_fatal(FailedCreateTempdir { err }));
  74     let metadata_tmpdir = MaybeTempDir::new(metadata_tmpdir, tcx.sess.opts.cg.save_temps);
  75     let metadata_filename = metadata_tmpdir.as_ref().join(METADATA_FILENAME);
  76
  77     // Always create a file at `metadata_filename`, even if we have nothing to write to it.
  78     // This simplifies the creation of the output `out_filename` when requested.
  79     match metadata_kind {
  80         MetadataKind::None => {
  81             std::fs::File::create(&metadata_filename).unwrap_or_else(|err| {
  82                 tcx.sess.emit_fatal(FailedCreateFile { filename: &metadata_filename, err });
  83             });
  84         }
  85         MetadataKind::Uncompressed | MetadataKind::Compressed => {
  86             encode_metadata(tcx, &metadata_filename);
  87         }
  88     };
  89
  90     let _prof_timer = tcx.sess.prof.generic_activity("write_crate_metadata");
  91
  92     // If the user requests metadata as output, rename `metadata_filename`
  93     // to the expected output `out_filename`.  The match above should ensure
  94     // this file always exists.
  95     let need_metadata_file = tcx.sess.opts.output_types.contains_key(&OutputType::Metadata);
  96     let (metadata_filename, metadata_tmpdir) = if need_metadata_file {
  97         if let Err(err) = non_durable_rename(&metadata_filename, &out_filename) {
  98             tcx.sess.emit_fatal(FailedWriteError { filename: out_filename, err });
  99         }
 100         if tcx.sess.opts.json_artifact_notifications {
 101             tcx.sess
 102                 .parse_sess
 103                 .span_diagnostic
 104                 .emit_artifact_notification(&out_filename, "metadata");
 105         }
 106         (out_filename, None)
 107     } else {
 108         (metadata_filename, Some(metadata_tmpdir))
 109     };
 110
 111     // Load metadata back to memory: codegen may need to include it in object files.
 112     let metadata =
 113         EncodedMetadata::from_path(metadata_filename, metadata_tmpdir).unwrap_or_else(|err| {
 114             tcx.sess.emit_fatal(FailedCreateEncodedMetadata { err });
 115         });
 116
 117     let need_metadata_module = metadata_kind == MetadataKind::Compressed;
 118
 119     (metadata, need_metadata_module)
 120 }
 121
 122 #[cfg(not(target_os = "linux"))]
 123 pub fn non_durable_rename(src: &Path, dst: &Path) -> std::io::Result<()> {
 124     std::fs::rename(src, dst)
 125 }
 126
 127 /// This function attempts to bypass the auto_da_alloc heuristic implemented by some filesystems
 128 /// such as btrfs and ext4. When renaming over a file that already exists then they will "helpfully"
 129 /// write back the source file before committing the rename in case a developer forgot some of
 130 /// the fsyncs in the open/write/fsync(file)/rename/fsync(dir) dance for atomic file updates.
 131 ///
 132 /// To avoid triggering this heuristic we delete the destination first, if it exists.
 133 /// The cost of an extra syscall is much lower than getting descheduled for the sync IO.
 134 #[cfg(target_os = "linux")]
 135 pub fn non_durable_rename(src: &Path, dst: &Path) -> std::io::Result<()> {
 136     let _ = std::fs::remove_file(dst);
 137     std::fs::rename(src, dst)
 138 }