mirror of
https://github.com/privatevoid-net/nix-super.git
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447089a5f6
Nix. This is to prevent Berkeley DB from becoming wedged. Unfortunately it is not possible to throw C++ exceptions from a signal handler. In fact, you can't do much of anything except change variables of type `volatile sig_atomic_t'. So we set an interrupt flag in the signal handler and check it at various strategic locations in the code (by calling checkInterrupt()). Since this is unlikely to cover all cases (e.g., (semi-)infinite loops), sometimes SIGTERM may now be required to kill Nix.
480 lines
13 KiB
C++
480 lines
13 KiB
C++
#include <iostream>
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#include <algorithm>
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#include <sys/wait.h>
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#include <unistd.h>
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#include "store.hh"
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#include "globals.hh"
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#include "db.hh"
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#include "archive.hh"
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#include "pathlocks.hh"
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/* Nix database. */
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static Database nixDB;
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/* Database tables. */
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/* dbValidPaths :: Path -> ()
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The existence of a key $p$ indicates that path $p$ is valid (that
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is, produced by a succesful build). */
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static TableId dbValidPaths;
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/* dbSuccessors :: Path -> Path
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Each pair $(p_1, p_2)$ in this mapping records the fact that the
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Nix expression stored at path $p_1$ has a successor expression
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stored at path $p_2$.
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Note that a term $y$ is a successor of $x$ iff there exists a
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sequence of rewrite steps that rewrites $x$ into $y$.
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*/
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static TableId dbSuccessors;
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/* dbSuccessorsRev :: Path -> [Path]
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The reverse mapping of dbSuccessors (i.e., it stores the
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predecessors of a Nix expression).
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*/
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static TableId dbSuccessorsRev;
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/* dbSubstitutes :: Path -> [Path]
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Each pair $(p, [ps])$ tells Nix that it can realise any of the
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Nix expressions stored at paths $ps$ to produce a path $p$.
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The main purpose of this is for distributed caching of derivates.
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One system can compute a derivate and put it on a website (as a Nix
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archive), for instance, and then another system can register a
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substitute for that derivate. The substitute in this case might be
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a Nix expression that fetches the Nix archive.
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*/
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static TableId dbSubstitutes;
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/* dbSubstitutesRev :: Path -> [Path]
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The reverse mapping of dbSubstitutes.
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*/
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static TableId dbSubstitutesRev;
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void openDB()
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{
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nixDB.open(nixDBPath);
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dbValidPaths = nixDB.openTable("validpaths");
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dbSuccessors = nixDB.openTable("successors");
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dbSuccessorsRev = nixDB.openTable("successors-rev");
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dbSubstitutes = nixDB.openTable("substitutes");
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dbSubstitutesRev = nixDB.openTable("substitutes-rev");
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}
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void initDB()
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{
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}
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void createStoreTransaction(Transaction & txn)
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{
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Transaction txn2(nixDB);
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txn2.moveTo(txn);
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}
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/* Path copying. */
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struct CopySink : DumpSink
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{
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int fd;
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virtual void operator () (const unsigned char * data, unsigned int len)
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{
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writeFull(fd, data, len);
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}
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};
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struct CopySource : RestoreSource
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{
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int fd;
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virtual void operator () (unsigned char * data, unsigned int len)
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{
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readFull(fd, data, len);
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}
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};
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void copyPath(const Path & src, const Path & dst)
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{
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debug(format("copying `%1%' to `%2%'") % src % dst);
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/* Unfortunately C++ doesn't support coprocedures, so we have no
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nice way to chain CopySink and CopySource together. Instead we
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fork off a child to run the sink. (Fork-less platforms should
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use a thread). */
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/* Create a pipe. */
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int fds[2];
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if (pipe(fds) == -1) throw SysError("creating pipe");
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/* Fork. */
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pid_t pid;
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switch (pid = fork()) {
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case -1:
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throw SysError("unable to fork");
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case 0: /* child */
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try {
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close(fds[1]);
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CopySource source;
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source.fd = fds[0];
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restorePath(dst, source);
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_exit(0);
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} catch (exception & e) {
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cerr << "error: " << e.what() << endl;
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}
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_exit(1);
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}
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close(fds[0]);
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/* Parent. */
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CopySink sink;
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sink.fd = fds[1];
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dumpPath(src, sink);
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/* Wait for the child to finish. */
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int status;
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if (waitpid(pid, &status, 0) != pid)
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throw SysError("waiting for child");
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if (!WIFEXITED(status) || WEXITSTATUS(status) != 0)
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throw Error("cannot copy file: child died");
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}
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static bool isValidPathTxn(const Path & path, const Transaction & txn)
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{
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string s;
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return nixDB.queryString(txn, dbValidPaths, path, s);
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}
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bool isValidPath(const Path & path)
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{
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return isValidPathTxn(path, noTxn);
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}
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static bool isUsablePathTxn(const Path & path, const Transaction & txn)
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{
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if (isValidPathTxn(path, txn)) return true;
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Paths subs;
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nixDB.queryStrings(txn, dbSubstitutes, path, subs);
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return subs.size() > 0;
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}
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void registerSuccessor(const Transaction & txn,
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const Path & srcPath, const Path & sucPath)
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{
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if (!isUsablePathTxn(sucPath, txn)) throw Error(
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format("path `%1%' cannot be a successor, since it is not usable")
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% sucPath);
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Path known;
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if (nixDB.queryString(txn, dbSuccessors, srcPath, known) &&
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known != sucPath)
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{
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throw Error(format(
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"the `impossible' happened: expression in path "
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"`%1%' appears to have multiple successors "
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"(known `%2%', new `%3%'")
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% srcPath % known % sucPath);
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}
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Paths revs;
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nixDB.queryStrings(txn, dbSuccessorsRev, sucPath, revs);
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if (find(revs.begin(), revs.end(), srcPath) == revs.end())
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revs.push_back(srcPath);
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nixDB.setString(txn, dbSuccessors, srcPath, sucPath);
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nixDB.setStrings(txn, dbSuccessorsRev, sucPath, revs);
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}
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bool querySuccessor(const Path & srcPath, Path & sucPath)
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{
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return nixDB.queryString(noTxn, dbSuccessors, srcPath, sucPath);
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}
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Paths queryPredecessors(const Path & sucPath)
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{
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Paths revs;
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nixDB.queryStrings(noTxn, dbSuccessorsRev, sucPath, revs);
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return revs;
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}
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void registerSubstitute(const Path & srcPath, const Path & subPath)
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{
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if (!isValidPathTxn(subPath, noTxn)) throw Error(
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format("path `%1%' cannot be a substitute, since it is not valid")
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% subPath);
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Transaction txn(nixDB);
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Paths subs;
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nixDB.queryStrings(txn, dbSubstitutes, srcPath, subs);
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if (find(subs.begin(), subs.end(), subPath) != subs.end()) {
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/* Nothing to do if the substitute is already known. */
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txn.abort();
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return;
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}
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subs.push_front(subPath); /* new substitutes take precedence */
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Paths revs;
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nixDB.queryStrings(txn, dbSubstitutesRev, subPath, revs);
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if (find(revs.begin(), revs.end(), srcPath) == revs.end())
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revs.push_back(srcPath);
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nixDB.setStrings(txn, dbSubstitutes, srcPath, subs);
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nixDB.setStrings(txn, dbSubstitutesRev, subPath, revs);
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txn.commit();
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}
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Paths querySubstitutes(const Path & srcPath)
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{
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Paths subPaths;
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nixDB.queryStrings(noTxn, dbSubstitutes, srcPath, subPaths);
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return subPaths;
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}
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void registerValidPath(const Transaction & txn, const Path & _path)
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{
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Path path(canonPath(_path));
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debug(format("registering path `%1%'") % path);
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nixDB.setString(txn, dbValidPaths, path, "");
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}
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static void setOrClearStrings(Transaction & txn,
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TableId table, const string & key, const Strings & value)
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{
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if (value.size() > 0)
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nixDB.setStrings(txn, table, key, value);
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else
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nixDB.delPair(txn, table, key);
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}
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static void invalidatePath(const Path & path, Transaction & txn)
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{
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debug(format("unregistering path `%1%'") % path);
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nixDB.delPair(txn, dbValidPaths, path);
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/* Remove any successor mappings to this path (but not *from*
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it). */
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Paths revs;
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nixDB.queryStrings(txn, dbSuccessorsRev, path, revs);
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for (Paths::iterator i = revs.begin(); i != revs.end(); ++i)
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nixDB.delPair(txn, dbSuccessors, *i);
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nixDB.delPair(txn, dbSuccessorsRev, path);
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/* Remove any substitute mappings to this path. */
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revs.clear();
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nixDB.queryStrings(txn, dbSubstitutesRev, path, revs);
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for (Paths::iterator i = revs.begin(); i != revs.end(); ++i) {
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Paths subs;
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nixDB.queryStrings(txn, dbSubstitutes, *i, subs);
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if (find(subs.begin(), subs.end(), path) == subs.end())
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throw Error("integrity error in substitutes mapping");
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subs.remove(path);
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setOrClearStrings(txn, dbSubstitutes, *i, subs);
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/* If path *i now has no substitutes left, and is not valid,
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then it too should be invalidated. This is because it may
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be a substitute or successor. */
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if (subs.size() == 0 && !isValidPathTxn(*i, txn))
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invalidatePath(*i, txn);
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}
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nixDB.delPair(txn, dbSubstitutesRev, path);
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}
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static bool isInPrefix(const string & path, const string & _prefix)
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{
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string prefix = canonPath(_prefix + "/");
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return string(path, 0, prefix.size()) == prefix;
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}
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Path addToStore(const Path & _srcPath)
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{
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Path srcPath(absPath(_srcPath));
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debug(format("adding `%1%' to the store") % srcPath);
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Hash h = hashPath(srcPath);
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string baseName = baseNameOf(srcPath);
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Path dstPath = canonPath(nixStore + "/" + (string) h + "-" + baseName);
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if (!isValidPath(dstPath)) {
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/* The first check above is an optimisation to prevent
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unnecessary lock acquisition. */
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PathSet lockPaths;
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lockPaths.insert(dstPath);
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PathLocks outputLock(lockPaths);
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if (!isValidPath(dstPath)) {
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copyPath(srcPath, dstPath);
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Transaction txn(nixDB);
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registerValidPath(txn, dstPath);
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txn.commit();
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}
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outputLock.setDeletion(true);
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}
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return dstPath;
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}
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void addTextToStore(const Path & dstPath, const string & s)
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{
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if (!isValidPath(dstPath)) {
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PathSet lockPaths;
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lockPaths.insert(dstPath);
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PathLocks outputLock(lockPaths);
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if (!isValidPath(dstPath)) {
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writeStringToFile(dstPath, s);
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Transaction txn(nixDB);
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registerValidPath(txn, dstPath);
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txn.commit();
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}
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outputLock.setDeletion(true);
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}
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}
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void deleteFromStore(const Path & _path)
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{
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Path path(canonPath(_path));
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if (!isInPrefix(path, nixStore))
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throw Error(format("path `%1%' is not in the store") % path);
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Transaction txn(nixDB);
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invalidatePath(path, txn);
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txn.commit();
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deletePath(path);
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}
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void verifyStore()
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{
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Transaction txn(nixDB);
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Paths paths;
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PathSet validPaths;
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nixDB.enumTable(txn, dbValidPaths, paths);
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for (Paths::iterator i = paths.begin(); i != paths.end(); ++i) {
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Path path = *i;
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if (!pathExists(path)) {
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printMsg(lvlError, format("path `%1%' disappeared") % path);
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invalidatePath(path, txn);
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} else
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validPaths.insert(path);
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}
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/* !!! the code below does not allow transitive substitutes.
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I.e., if B is a substitute of A, then B must be a valid path.
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B cannot itself be invalid but have a substitute. */
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/* "Usable" paths are those that are valid or have a substitute.
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These are the paths that are allowed to appear in the
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right-hand side of a sute mapping. */
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PathSet usablePaths(validPaths);
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/* Check that the values of the substitute mappings are valid
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paths. */
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Paths subs;
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nixDB.enumTable(txn, dbSubstitutes, subs);
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for (Paths::iterator i = subs.begin(); i != subs.end(); ++i) {
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Paths subPaths, subPaths2;
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nixDB.queryStrings(txn, dbSubstitutes, *i, subPaths);
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for (Paths::iterator j = subPaths.begin(); j != subPaths.end(); ++j)
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if (validPaths.find(*j) == validPaths.end())
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printMsg(lvlError,
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format("found substitute mapping to non-existent path `%1%'") % *j);
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else
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subPaths2.push_back(*j);
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if (subPaths.size() != subPaths2.size())
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setOrClearStrings(txn, dbSubstitutes, *i, subPaths2);
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if (subPaths2.size() > 0)
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usablePaths.insert(*i);
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}
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/* Check that the keys of the reverse substitute mappings are
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valid paths. */
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Paths rsubs;
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nixDB.enumTable(txn, dbSubstitutesRev, rsubs);
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for (Paths::iterator i = rsubs.begin(); i != rsubs.end(); ++i) {
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if (validPaths.find(*i) == validPaths.end()) {
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printMsg(lvlError,
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format("found reverse substitute mapping for non-existent path `%1%'") % *i);
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nixDB.delPair(txn, dbSubstitutesRev, *i);
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}
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}
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/* Check that the values of the successor mappings are usable
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paths. */
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Paths sucs;
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nixDB.enumTable(txn, dbSuccessors, sucs);
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for (Paths::iterator i = sucs.begin(); i != sucs.end(); ++i) {
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/* Note that *i itself does not have to be valid, just its
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successor. */
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Path sucPath;
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if (nixDB.queryString(txn, dbSuccessors, *i, sucPath) &&
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usablePaths.find(sucPath) == usablePaths.end())
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{
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printMsg(lvlError,
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format("found successor mapping to non-existent path `%1%'") % sucPath);
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nixDB.delPair(txn, dbSuccessors, *i);
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}
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}
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/* Check that the keys of the reverse successor mappings are valid
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paths. */
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Paths rsucs;
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nixDB.enumTable(txn, dbSuccessorsRev, rsucs);
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for (Paths::iterator i = rsucs.begin(); i != rsucs.end(); ++i) {
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if (usablePaths.find(*i) == usablePaths.end()) {
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printMsg(lvlError,
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format("found reverse successor mapping for non-existent path `%1%'") % *i);
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nixDB.delPair(txn, dbSuccessorsRev, *i);
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}
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}
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txn.commit();
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}
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