tvl-depot/src/libstore/store.cc

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#include <iostream>
#include <sys/wait.h>
#include <unistd.h>
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#include "store.hh"
#include "globals.hh"
#include "db.hh"
#include "archive.hh"
#include "pathlocks.hh"
/* Nix database. */
static Database nixDB;
/* Database tables. */
/* dbValidPaths :: Path -> ()
The existence of a key $p$ indicates that path $p$ is valid (that
is, produced by a succesful build). */
static TableId dbValidPaths;
/* dbSuccessors :: Path -> Path
Each pair $(p_1, p_2)$ in this mapping records the fact that the
Nix expression stored at path $p_1$ has a successor expression
stored at path $p_2$.
Note that a term $y$ is a successor of $x$ iff there exists a
sequence of rewrite steps that rewrites $x$ into $y$.
*/
static TableId dbSuccessors;
/* dbSuccessorsRev :: Path -> [Path]
The reverse mapping of dbSuccessors (i.e., it stores the
predecessors of a Nix expression).
*/
static TableId dbSuccessorsRev;
/* dbSubstitutes :: Path -> [Path]
Each pair $(p, [ps])$ tells Nix that it can realise any of the
Nix expressions stored at paths $ps$ to produce a path $p$.
The main purpose of this is for distributed caching of derivates.
One system can compute a derivate and put it on a website (as a Nix
archive), for instance, and then another system can register a
substitute for that derivate. The substitute in this case might be
a Nix expression that fetches the Nix archive.
*/
static TableId dbSubstitutes;
/* dbSubstitutesRev :: Path -> [Path]
The reverse mapping of dbSubstitutes.
*/
static TableId dbSubstitutesRev;
void openDB()
{
nixDB.open(nixDBPath);
dbValidPaths = nixDB.openTable("validpaths");
dbSuccessors = nixDB.openTable("successors");
dbSuccessorsRev = nixDB.openTable("successors-rev");
dbSubstitutes = nixDB.openTable("substitutes");
dbSubstitutesRev = nixDB.openTable("substitutes-rev");
}
void initDB()
{
}
void createStoreTransaction(Transaction & txn)
{
Transaction txn2(nixDB);
txn2.moveTo(txn);
}
/* Path copying. */
struct CopySink : DumpSink
{
int fd;
virtual void operator () (const unsigned char * data, unsigned int len)
{
writeFull(fd, data, len);
}
};
struct CopySource : RestoreSource
{
int fd;
virtual void operator () (unsigned char * data, unsigned int len)
{
readFull(fd, data, len);
}
};
void copyPath(const Path & src, const Path & dst)
{
debug(format("copying `%1%' to `%2%'") % src % dst);
/* Unfortunately C++ doesn't support coprocedures, so we have no
nice way to chain CopySink and CopySource together. Instead we
fork off a child to run the sink. (Fork-less platforms should
use a thread). */
/* Create a pipe. */
int fds[2];
if (pipe(fds) == -1) throw SysError("creating pipe");
/* Fork. */
pid_t pid;
switch (pid = fork()) {
case -1:
throw SysError("unable to fork");
case 0: /* child */
try {
close(fds[1]);
CopySource source;
source.fd = fds[0];
restorePath(dst, source);
_exit(0);
} catch (exception & e) {
cerr << "error: " << e.what() << endl;
}
_exit(1);
}
close(fds[0]);
/* Parent. */
CopySink sink;
sink.fd = fds[1];
dumpPath(src, sink);
/* Wait for the child to finish. */
int status;
if (waitpid(pid, &status, 0) != pid)
throw SysError("waiting for child");
if (!WIFEXITED(status) || WEXITSTATUS(status) != 0)
throw Error("cannot copy file: child died");
}
void registerSuccessor(const Transaction & txn,
const Path & srcPath, const Path & sucPath)
{
Path known;
if (nixDB.queryString(txn, dbSuccessors, srcPath, known) &&
known != sucPath)
{
throw Error(format(
"the `impossible' happened: expression in path "
"`%1%' appears to have multiple successors "
"(known `%2%', new `%3%'")
% srcPath % known % sucPath);
}
Paths revs;
nixDB.queryStrings(txn, dbSuccessorsRev, sucPath, revs);
if (find(revs.begin(), revs.end(), srcPath) == revs.end())
revs.push_back(srcPath);
nixDB.setString(txn, dbSuccessors, srcPath, sucPath);
nixDB.setStrings(txn, dbSuccessorsRev, sucPath, revs);
}
bool querySuccessor(const Path & srcPath, Path & sucPath)
{
return nixDB.queryString(noTxn, dbSuccessors, srcPath, sucPath);
}
Paths queryPredecessors(const Path & sucPath)
{
Paths revs;
nixDB.queryStrings(noTxn, dbSuccessorsRev, sucPath, revs);
return revs;
}
void registerSubstitute(const Path & srcPath, const Path & subPath)
{
Transaction txn(nixDB);
Paths subs;
nixDB.queryStrings(txn, dbSubstitutes, srcPath, subs);
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if (find(subs.begin(), subs.end(), subPath) != subs.end()) {
/* Nothing to do if the substitute is already known. */
txn.abort();
return;
}
subs.push_front(subPath); /* new substitutes take precedence */
Paths revs;
nixDB.queryStrings(txn, dbSubstitutesRev, subPath, revs);
if (find(revs.begin(), revs.end(), srcPath) == revs.end())
revs.push_back(srcPath);
nixDB.setStrings(txn, dbSubstitutes, srcPath, subs);
nixDB.setStrings(txn, dbSubstitutesRev, subPath, revs);
txn.commit();
}
Paths querySubstitutes(const Path & srcPath)
{
Paths subPaths;
nixDB.queryStrings(noTxn, dbSubstitutes, srcPath, subPaths);
return subPaths;
}
void registerValidPath(const Transaction & txn, const Path & _path)
{
Path path(canonPath(_path));
debug(format("registering path `%1%'") % path);
nixDB.setString(txn, dbValidPaths, path, "");
}
bool isValidPath(const Path & path)
{
string s;
return nixDB.queryString(noTxn, dbValidPaths, path, s);
}
static void invalidatePath(const Path & path, Transaction & txn)
{
debug(format("unregistering path `%1%'") % path);
nixDB.delPair(txn, dbValidPaths, path);
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/* Remove any successor mappings to this path (but not *from*
it). */
Paths revs;
nixDB.queryStrings(txn, dbSuccessorsRev, path, revs);
for (Paths::iterator i = revs.begin(); i != revs.end(); ++i)
nixDB.delPair(txn, dbSuccessors, *i);
nixDB.delPair(txn, dbSuccessorsRev, path);
/* Remove any substitute mappings to this path. */
revs.clear();
nixDB.queryStrings(txn, dbSubstitutesRev, path, revs);
for (Paths::iterator i = revs.begin(); i != revs.end(); ++i) {
Paths subs;
nixDB.queryStrings(txn, dbSubstitutes, *i, subs);
remove(subs.begin(), subs.end(), path);
if (subs.size() > 0)
nixDB.setStrings(txn, dbSubstitutes, *i, subs);
else
nixDB.delPair(txn, dbSubstitutes, *i);
}
nixDB.delPair(txn, dbSubstitutesRev, path);
}
static bool isInPrefix(const string & path, const string & _prefix)
{
string prefix = canonPath(_prefix + "/");
return string(path, 0, prefix.size()) == prefix;
}
Path addToStore(const Path & _srcPath)
{
Path srcPath(absPath(_srcPath));
debug(format("adding `%1%' to the store") % srcPath);
Hash h = hashPath(srcPath);
string baseName = baseNameOf(srcPath);
Path dstPath = canonPath(nixStore + "/" + (string) h + "-" + baseName);
if (!isValidPath(dstPath)) {
/* The first check above is an optimisation to prevent
unnecessary lock acquisition. */
PathSet lockPaths;
lockPaths.insert(dstPath);
PathLocks outputLock(lockPaths);
if (!isValidPath(dstPath)) {
copyPath(srcPath, dstPath);
Transaction txn(nixDB);
registerValidPath(txn, dstPath);
txn.commit();
}
outputLock.setDeletion(true);
}
return dstPath;
}
void addTextToStore(const Path & dstPath, const string & s)
{
if (!isValidPath(dstPath)) {
PathSet lockPaths;
lockPaths.insert(dstPath);
PathLocks outputLock(lockPaths);
if (!isValidPath(dstPath)) {
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writeStringToFile(dstPath, s);
Transaction txn(nixDB);
registerValidPath(txn, dstPath);
txn.commit();
}
outputLock.setDeletion(true);
}
}
void deleteFromStore(const Path & _path)
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{
Path path(canonPath(_path));
if (!isInPrefix(path, nixStore))
throw Error(format("path `%1%' is not in the store") % path);
Transaction txn(nixDB);
invalidatePath(path, txn);
txn.commit();
deletePath(path);
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}
void verifyStore()
{
Transaction txn(nixDB);
Paths paths;
PathSet validPaths;
nixDB.enumTable(txn, dbValidPaths, paths);
for (Paths::iterator i = paths.begin(); i != paths.end(); ++i)
{
Path path = *i;
if (!pathExists(path)) {
debug(format("path `%1%' disappeared") % path);
invalidatePath(path, txn);
} else
validPaths.insert(path);
}
Paths sucs;
nixDB.enumTable(txn, dbSuccessors, sucs);
for (Paths::iterator i = sucs.begin(); i != sucs.end(); ++i) {
/* Note that *i itself does not have to be valid, just its
successor. */
Path sucPath;
if (nixDB.queryString(txn, dbSuccessors, *i, sucPath) &&
validPaths.find(sucPath) == validPaths.end())
{
debug(format("found successor mapping to non-existent path `%1%'") % sucPath);
nixDB.delPair(txn, dbSuccessors, *i);
}
}
Paths rsucs;
nixDB.enumTable(txn, dbSuccessorsRev, rsucs);
for (Paths::iterator i = rsucs.begin(); i != rsucs.end(); ++i) {
if (validPaths.find(*i) == validPaths.end()) {
debug(format("found reverse successor mapping for non-existent path `%1%'") % *i);
nixDB.delPair(txn, dbSuccessorsRev, *i);
}
}
#if 0
Paths sucs;
nixDB.enumTable(txn, dbSuccessors, sucs);
for (Paths::iterator i = sucs.begin(); i != sucs.end(); i++) {
Path srcPath = *i;
Path sucPath;
if (!nixDB.queryString(txn, dbSuccessors, srcPath, sucPath)) abort();
Paths revs;
nixDB.queryStrings(txn, dbSuccessorsRev, sucPath, revs);
if (find(revs.begin(), revs.end(), srcPath) == revs.end()) {
debug(format("reverse successor mapping from `%1%' to `%2%' missing")
% srcPath % sucPath);
revs.push_back(srcPath);
nixDB.setStrings(txn, dbSuccessorsRev, sucPath, revs);
}
}
#endif
txn.commit();
}