use crate::errors::{ FailedCreateEncodedMetadata, FailedCreateFile, FailedCreateTempdir, FailedWriteError, }; use crate::{encode_metadata, EncodedMetadata}; use rustc_data_structures::temp_dir::MaybeTempDir; use rustc_hir::def_id::LOCAL_CRATE; use rustc_middle::ty::TyCtxt; use rustc_session::config::{CrateType, OutputFilenames, OutputType}; use rustc_session::output::filename_for_metadata; use rustc_session::Session; use tempfile::Builder as TempFileBuilder; use std::fs; use std::path::{Path, PathBuf}; // FIXME(eddyb) maybe include the crate name in this? pub const METADATA_FILENAME: &str = "lib.rmeta"; /// We use a temp directory here to avoid races between concurrent rustc processes, /// such as builds in the same directory using the same filename for metadata while /// building an `.rlib` (stomping over one another), or writing an `.rmeta` into a /// directory being searched for `extern crate` (observing an incomplete file). /// The returned path is the temporary file containing the complete metadata. pub fn emit_metadata(sess: &Session, metadata: &[u8], tmpdir: &MaybeTempDir) -> PathBuf { let out_filename = tmpdir.as_ref().join(METADATA_FILENAME); let result = fs::write(&out_filename, metadata); if let Err(err) = result { sess.emit_fatal(FailedWriteError { filename: out_filename, err }); } out_filename } pub fn encode_and_write_metadata( tcx: TyCtxt<'_>, outputs: &OutputFilenames, ) -> (EncodedMetadata, bool) { #[derive(PartialEq, Eq, PartialOrd, Ord)] enum MetadataKind { None, Uncompressed, Compressed, } let metadata_kind = tcx .sess .crate_types() .iter() .map(|ty| match *ty { CrateType::Executable | CrateType::Staticlib | CrateType::Cdylib => MetadataKind::None, CrateType::Rlib => MetadataKind::Uncompressed, CrateType::Dylib | CrateType::ProcMacro => MetadataKind::Compressed, }) .max() .unwrap_or(MetadataKind::None); let crate_name = tcx.crate_name(LOCAL_CRATE); let out_filename = filename_for_metadata(tcx.sess, crate_name.as_str(), outputs); // To avoid races with another rustc process scanning the output directory, // we need to write the file somewhere else and atomically move it to its // final destination, with an `fs::rename` call. In order for the rename to // always succeed, the temporary file needs to be on the same filesystem, // which is why we create it inside the output directory specifically. let metadata_tmpdir = TempFileBuilder::new() .prefix("rmeta") .tempdir_in(out_filename.parent().unwrap_or_else(|| Path::new(""))) .unwrap_or_else(|err| tcx.sess.emit_fatal(FailedCreateTempdir { err })); let metadata_tmpdir = MaybeTempDir::new(metadata_tmpdir, tcx.sess.opts.cg.save_temps); let metadata_filename = metadata_tmpdir.as_ref().join(METADATA_FILENAME); // Always create a file at `metadata_filename`, even if we have nothing to write to it. // This simplifies the creation of the output `out_filename` when requested. match metadata_kind { MetadataKind::None => { std::fs::File::create(&metadata_filename).unwrap_or_else(|err| { tcx.sess.emit_fatal(FailedCreateFile { filename: &metadata_filename, err }); }); } MetadataKind::Uncompressed | MetadataKind::Compressed => { encode_metadata(tcx, &metadata_filename); } }; let _prof_timer = tcx.sess.prof.generic_activity("write_crate_metadata"); // If the user requests metadata as output, rename `metadata_filename` // to the expected output `out_filename`. The match above should ensure // this file always exists. let need_metadata_file = tcx.sess.opts.output_types.contains_key(&OutputType::Metadata); let (metadata_filename, metadata_tmpdir) = if need_metadata_file { if let Err(err) = non_durable_rename(&metadata_filename, &out_filename) { tcx.sess.emit_fatal(FailedWriteError { filename: out_filename, err }); } if tcx.sess.opts.json_artifact_notifications { tcx.sess .parse_sess .span_diagnostic .emit_artifact_notification(&out_filename, "metadata"); } (out_filename, None) } else { (metadata_filename, Some(metadata_tmpdir)) }; // Load metadata back to memory: codegen may need to include it in object files. let metadata = EncodedMetadata::from_path(metadata_filename, metadata_tmpdir).unwrap_or_else(|err| { tcx.sess.emit_fatal(FailedCreateEncodedMetadata { err }); }); let need_metadata_module = metadata_kind == MetadataKind::Compressed; (metadata, need_metadata_module) } #[cfg(not(target_os = "linux"))] pub fn non_durable_rename(src: &Path, dst: &Path) -> std::io::Result<()> { std::fs::rename(src, dst) } /// This function attempts to bypass the auto_da_alloc heuristic implemented by some filesystems /// such as btrfs and ext4. When renaming over a file that already exists then they will "helpfully" /// write back the source file before committing the rename in case a developer forgot some of /// the fsyncs in the open/write/fsync(file)/rename/fsync(dir) dance for atomic file updates. /// /// To avoid triggering this heuristic we delete the destination first, if it exists. /// The cost of an extra syscall is much lower than getting descheduled for the sync IO. #[cfg(target_os = "linux")] pub fn non_durable_rename(src: &Path, dst: &Path) -> std::io::Result<()> { let _ = std::fs::remove_file(dst); std::fs::rename(src, dst) }