forked from lix-project/lix
5c38c863bd
Nix-env failed to call addPermRoot(), which is necessary to safely
add a new root. So if nix-env started after and finished before the
garbage collector, the user environment (plus all other new stuff)
it built might be garbage collected, leading to a dangling symlink
chain in ~/.nix-profile...
* Be more explicit if we block on the GC lock ("waiting for the big
garbage collector lock...").
* Don't loop trying to create a new generation. It's not necessary
anymore since profiles are locked nowadays.
136 lines
3.7 KiB
C++
136 lines
3.7 KiB
C++
#include "profiles.hh"
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#include "util.hh"
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#include "gc.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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#include <stdio.h>
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namespace nix {
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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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string::size_type 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 makeName(const Path & profile, unsigned int num,
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Path & outLink)
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{
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Path prefix = (format("%1%-%2%") % profile % num).str();
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outLink = prefix + "-link";
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}
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Path createGeneration(Path profile, Path outPath)
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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. Note that addPermRoot() blocks if
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the garbage collector is running to prevent the stuff we've
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build from moving from the temporary roots (which the GC knows)
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to the permanent roots (of which the GC would have a stale
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view). If we didn't do it this way, the GC might remove the
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user environment etc. we've just built. */
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Path generation;
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makeName(profile, num + 1, generation);
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addPermRoot(outPath, generation, false, true);
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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;
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makeName(profile, gen, generation);
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removeFile(generation);
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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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}
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