lix/src/store.cc

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#include <iostream>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/wait.h>
#include <fcntl.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);
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);
revs.push_back(srcPath);
nixDB.setStrings(txn, dbSubstitutes, srcPath, subs);
nixDB.setStrings(txn, dbSubstitutesRev, subPath, revs);
txn.commit();
}
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);
}
void unregisterValidPath(const Path & _path)
{
Path path(canonPath(_path));
Transaction txn(nixDB);
debug(format("unregistering path `%1%'") % path);
nixDB.delPair(txn, dbValidPaths, path);
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txn.commit();
}
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();
}
}
return dstPath;
}
void addTextToStore(const Path & dstPath, const string & s)
{
if (!isValidPath(dstPath)) {
/* !!! locking? -> parallel writes are probably idempotent */
int fd = open(dstPath.c_str(), O_CREAT | O_EXCL | O_WRONLY, 0666);
if (fd == -1) throw SysError(format("creating store file `%1%'") % dstPath);
if (write(fd, s.c_str(), s.size()) != (ssize_t) s.size())
throw SysError(format("writing store file `%1%'") % dstPath);
close(fd); /* !!! close on exception */
Transaction txn(nixDB);
registerValidPath(txn, dstPath);
txn.commit();
}
}
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);
unregisterValidPath(path);
deletePath(path);
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}
void verifyStore()
{
Transaction txn(nixDB);
Paths paths;
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);
nixDB.delPair(txn, dbValidPaths, path);
nixDB.delPair(txn, dbSuccessorsRev, path);
nixDB.delPair(txn, dbSubstitutesRev, path);
}
}
#if 0
Strings subs;
nixDB.enumTable(txn, dbSubstitutes, subs);
for (Strings::iterator i = subs.begin();
i != subs.end(); i++)
{
FSId srcId = parseHash(*i);
Strings subIds;
nixDB.queryStrings(txn, dbSubstitutes, srcId, subIds);
for (Strings::iterator j = subIds.begin();
j != subIds.end(); )
{
FSId subId = parseHash(*j);
Strings subPaths;
nixDB.queryStrings(txn, dbId2Paths, subId, subPaths);
if (subPaths.size() == 0) {
debug(format("erasing substitute %1% for %2%")
% (string) subId % (string) srcId);
j = subIds.erase(j);
} else j++;
}
nixDB.setStrings(txn, dbSubstitutes, srcId, subIds);
}
#endif
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);
}
}
txn.commit();
}