863dcff6c5
representation of closures as ATerms in the Nix store. Instead, the
file system pointer graph is now stored in the Nix database. This
has many advantages:
- It greatly simplifies the implementation (we can drop the notion
of `successors', and so on).
- It makes registering roots for the garbage collector much easier.
Instead of specifying the closure expression as a root, you can
simply specify the store path that must be retained as a root.
This could not be done previously, since there was no way to find
the closure store expression containing a given store path.
- Better traceability: it is now possible to query what paths are
referenced by a path, and what paths refer to a path.
131 lines
3.7 KiB
C++
131 lines
3.7 KiB
C++
#include "profiles.hh"
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#include <sys/types.h>
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#include <sys/stat.h>
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#include <unistd.h>
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#include <errno.h>
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static bool cmpGensByNumber(const Generation & a, const Generation & b)
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{
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return a.number < b.number;
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}
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/* Parse a generation name of the format
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`<profilename>-<number>-link'. */
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static int parseName(const string & profileName, const string & name)
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{
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if (string(name, 0, profileName.size() + 1) != profileName + "-") return -1;
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string s = string(name, profileName.size() + 1);
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unsigned int p = s.find("-link");
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if (p == string::npos) return -1;
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int n;
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if (string2Int(string(s, 0, p), n) && n >= 0)
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return n;
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else
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return -1;
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}
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Generations findGenerations(Path profile, int & curGen)
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{
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Generations gens;
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Path profileDir = dirOf(profile);
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string profileName = baseNameOf(profile);
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Strings names = readDirectory(profileDir);
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for (Strings::iterator i = names.begin(); i != names.end(); ++i) {
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int n;
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if ((n = parseName(profileName, *i)) != -1) {
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Generation gen;
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gen.path = profileDir + "/" + *i;
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gen.number = n;
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struct stat st;
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if (lstat(gen.path.c_str(), &st) != 0)
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throw SysError(format("statting `%1%'") % gen.path);
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gen.creationTime = st.st_mtime;
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gens.push_back(gen);
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}
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}
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gens.sort(cmpGensByNumber);
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curGen = pathExists(profile)
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? parseName(profileName, readLink(profile))
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: -1;
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return gens;
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}
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static void makeNames(const Path & profile, unsigned int num,
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Path & generation, Path & gcrootDrv)
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{
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Path prefix = (format("%1%-%2%") % profile % num).str();
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generation = prefix + "-link";
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gcrootDrv = prefix + "-drv.gcroot";
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}
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Path createGeneration(Path profile, Path outPath, Path drvPath)
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{
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/* The new generation number should be higher than old the
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previous ones. */
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int dummy;
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Generations gens = findGenerations(profile, dummy);
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unsigned int num = gens.size() > 0 ? gens.front().number : 0;
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/* Create the new generation. */
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Path generation, gcrootDrv;
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while (1) {
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makeNames(profile, num, generation, gcrootDrv);
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if (symlink(outPath.c_str(), generation.c_str()) == 0) break;
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if (errno != EEXIST)
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throw SysError(format("creating symlink `%1%'") % generation);
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/* Somebody beat us to it, retry with a higher number. */
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num++;
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}
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writeStringToFile(gcrootDrv, drvPath);
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return generation;
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}
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static void removeFile(const Path & path)
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{
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if (remove(path.c_str()) == -1)
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throw SysError(format("cannot unlink `%1%'") % path);
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}
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void deleteGeneration(const Path & profile, unsigned int gen)
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{
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Path generation, gcrootDrv;
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makeNames(profile, gen, generation, gcrootDrv);
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removeFile(generation);
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if (pathExists(gcrootDrv)) removeFile(gcrootDrv);
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}
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void switchLink(Path link, Path target)
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{
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/* Hacky. */
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if (dirOf(target) == dirOf(link)) target = baseNameOf(target);
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Path tmp = canonPath(dirOf(link) + "/.new_" + baseNameOf(link));
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if (symlink(target.c_str(), tmp.c_str()) != 0)
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throw SysError(format("creating symlink `%1%'") % tmp);
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/* The rename() system call is supposed to be essentially atomic
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on Unix. That is, if we have links `current -> X' and
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`new_current -> Y', and we rename new_current to current, a
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process accessing current will see X or Y, but never a
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file-not-found or other error condition. This is sufficient to
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atomically switch user environments. */
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if (rename(tmp.c_str(), link.c_str()) != 0)
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throw SysError(format("renaming `%1%' to `%2%'") % tmp % link);
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}
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