From 1203e489263fe867d0a1ae3fd9270f40c8a1c24e Mon Sep 17 00:00:00 2001 From: Kjetil Orbekk Date: Sat, 29 Jan 2022 14:22:55 -0500 Subject: Store cached head in cached git repo The previous head caching implementation stored two paths in the local cache; one for the cached git repo and another textfile containing the resolved HEAD ref. This commit instead stores the resolved HEAD by setting the HEAD ref in the local cache appropriately. --- src/libfetchers/git.cc | 89 ++++++++++++++++++++++++++++++++------------------ 1 file changed, 58 insertions(+), 31 deletions(-) (limited to 'src') diff --git a/src/libfetchers/git.cc b/src/libfetchers/git.cc index 00a7b85d8..968cd642a 100644 --- a/src/libfetchers/git.cc +++ b/src/libfetchers/git.cc @@ -10,6 +10,7 @@ #include "fetch-settings.hh" #include +#include #include #include @@ -37,7 +38,19 @@ bool isCacheFileWithinTtl(const time_t now, const struct stat& st) { return st.st_mtime + settings.tarballTtl > now; } -Path getCachePath(std::string key) { +bool touchCacheFile(const Path& path, const time_t& touch_time) +{ + struct timeval times[2]; + times[0].tv_sec = touch_time; + times[0].tv_usec = 0; + times[1].tv_sec = touch_time; + times[1].tv_usec = 0; + + return lutimes(path.c_str(), times) == 0; +} + +Path getCachePath(std::string key) +{ return getCacheDir() + "/nix/gitv3/" + hashString(htSHA256, key).to_string(Base32, false); } @@ -80,32 +93,42 @@ std::optional readHead(const Path & path) return std::nullopt; } -std::optional readHeadCached(std::string actualUrl) +// Persist the HEAD ref from the remote repo in the local cached repo. +bool storeCachedHead(const std::string& actualUrl, const std::string& headRef) +{ + Path cacheDir = getCachePath(actualUrl); + try { + runProgram("git", true, { "-C", cacheDir, "symbolic-ref", "--", "HEAD", headRef }); + } catch (ExecError &e) { + if (!WIFEXITED(e.status)) throw; + return false; + } + /* No need to touch refs/HEAD, because `git symbolic-ref` updates the mtime. */ + return true; +} + +std::optional readHeadCached(const std::string& actualUrl) { // Create a cache path to store the branch of the HEAD ref. Append something // in front of the URL to prevent collision with the repository itself. - Path cachePath = getCachePath("|" + actualUrl); + Path cacheDir = getCachePath(actualUrl); + Path headRefFile = cacheDir + "/HEAD"; + time_t now = time(0); struct stat st; std::optional cachedRef; - if (stat(cachePath.c_str(), &st) == 0 && - // The file may be empty, because writeFile() is not atomic. - st.st_size > 0) { - - // The cached ref is persisted unconditionally (see below). - cachedRef = readFile(cachePath); - if (isCacheFileWithinTtl(now, st)) { + if (stat(headRefFile.c_str(), &st) == 0) { + cachedRef = readHead(cacheDir); + if (cachedRef != std::nullopt && + *cachedRef != gitInitialBranch && + isCacheFileWithinTtl(now, st)) { debug("using cached HEAD ref '%s' for repo '%s'", *cachedRef, actualUrl); return cachedRef; } } auto ref = readHead(actualUrl); - if (ref) { - debug("storing cached HEAD ref '%s' for repo '%s' at '%s'", *ref, actualUrl, cachePath); - createDirs(dirOf(cachePath)); - writeFile(cachePath, *ref); return ref; } @@ -438,15 +461,6 @@ struct GitInputScheme : InputScheme } } - if (!input.getRef()) { - auto head = isLocal ? readHead(actualUrl) : readHeadCached(actualUrl); - if (!head) { - warn("could not read HEAD ref from repo at '%s', using 'master'", actualUrl); - head = "master"; - } - input.attrs.insert_or_assign("ref", *head); - } - const Attrs unlockedAttrs({ {"type", cacheType}, {"name", name}, @@ -457,14 +471,30 @@ struct GitInputScheme : InputScheme Path repoDir; if (isLocal) { + if (!input.getRef()) { + auto head = readHead(actualUrl); + if (!head) { + warn("could not read HEAD ref from repo at '%s', using 'master'", actualUrl); + head = "master"; + } + input.attrs.insert_or_assign("ref", *head); + } if (!input.getRev()) input.attrs.insert_or_assign("rev", Hash::parseAny(chomp(runProgram("git", true, { "-C", actualUrl, "--git-dir", gitDir, "rev-parse", *input.getRef() })), htSHA1).gitRev()); repoDir = actualUrl; - } else { + const bool useHeadRef = !input.getRef(); + if (useHeadRef) { + auto head = readHeadCached(actualUrl); + if (!head) { + warn("could not read HEAD ref from repo at '%s', using 'master'", actualUrl); + head = "master"; + } + input.attrs.insert_or_assign("ref", *head); + } if (auto res = getCache()->lookup(store, unlockedAttrs)) { auto rev2 = Hash::parseAny(getStrAttr(res->first, "rev"), htSHA1); @@ -538,13 +568,10 @@ struct GitInputScheme : InputScheme warn("could not update local clone of Git repository '%s'; continuing with the most recent version", actualUrl); } - struct timeval times[2]; - times[0].tv_sec = now; - times[0].tv_usec = 0; - times[1].tv_sec = now; - times[1].tv_usec = 0; - - utimes(localRefFile.c_str(), times); + if (!touchCacheFile(localRefFile, now)) + warn("could not update mtime for file '%s': %s", localRefFile, strerror(errno)); + if (useHeadRef && !storeCachedHead(actualUrl, *input.getRef())) + warn("could not update cached head '%s' for '%s'", *input.getRef(), actualUrl); } if (!input.getRev()) -- cgit v1.2.3