lix/src/nix-env/profiles.cc
Eelco Dolstra 863dcff6c5 * Started removing closure store expressions, i.e., the explicit
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.
2005-01-19 11:16:11 +00:00

132 lines
3.7 KiB
C++

#include "profiles.hh"
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#include <errno.h>
static bool cmpGensByNumber(const Generation & a, const Generation & b)
{
return a.number < b.number;
}
/* Parse a generation name of the format
`<profilename>-<number>-link'. */
static int parseName(const string & profileName, const string & name)
{
if (string(name, 0, profileName.size() + 1) != profileName + "-") return -1;
string s = string(name, profileName.size() + 1);
unsigned int p = s.find("-link");
if (p == string::npos) return -1;
int n;
if (string2Int(string(s, 0, p), n) && n >= 0)
return n;
else
return -1;
}
Generations findGenerations(Path profile, int & curGen)
{
Generations gens;
Path profileDir = dirOf(profile);
string profileName = baseNameOf(profile);
Strings names = readDirectory(profileDir);
for (Strings::iterator i = names.begin(); i != names.end(); ++i) {
int n;
if ((n = parseName(profileName, *i)) != -1) {
Generation gen;
gen.path = profileDir + "/" + *i;
gen.number = n;
struct stat st;
if (lstat(gen.path.c_str(), &st) != 0)
throw SysError(format("statting `%1%'") % gen.path);
gen.creationTime = st.st_mtime;
gens.push_back(gen);
}
}
gens.sort(cmpGensByNumber);
curGen = pathExists(profile)
? parseName(profileName, readLink(profile))
: -1;
return gens;
}
static void makeNames(const Path & profile, unsigned int num,
Path & generation, Path & gcrootDrv)
{
Path prefix = (format("%1%-%2%") % profile % num).str();
generation = prefix + "-link";
gcrootDrv = prefix + "-drv.gcroot";
}
Path createGeneration(Path profile, Path outPath, Path drvPath)
{
/* The new generation number should be higher than old the
previous ones. */
int dummy;
Generations gens = findGenerations(profile, dummy);
unsigned int num = gens.size() > 0 ? gens.front().number : 0;
/* Create the new generation. */
Path generation, gcrootDrv;
while (1) {
makeNames(profile, num, generation, gcrootDrv);
if (symlink(outPath.c_str(), generation.c_str()) == 0) break;
if (errno != EEXIST)
throw SysError(format("creating symlink `%1%'") % generation);
/* Somebody beat us to it, retry with a higher number. */
num++;
}
writeStringToFile(gcrootDrv, drvPath);
return generation;
}
static void removeFile(const Path & path)
{
if (remove(path.c_str()) == -1)
throw SysError(format("cannot unlink `%1%'") % path);
}
void deleteGeneration(const Path & profile, unsigned int gen)
{
Path generation, gcrootDrv;
makeNames(profile, gen, generation, gcrootDrv);
removeFile(generation);
if (pathExists(gcrootDrv)) removeFile(gcrootDrv);
}
void switchLink(Path link, Path target)
{
/* Hacky. */
if (dirOf(target) == dirOf(link)) target = baseNameOf(target);
Path tmp = canonPath(dirOf(link) + "/.new_" + baseNameOf(link));
if (symlink(target.c_str(), tmp.c_str()) != 0)
throw SysError(format("creating symlink `%1%'") % tmp);
/* The rename() system call is supposed to be essentially atomic
on Unix. That is, if we have links `current -> X' and
`new_current -> Y', and we rename new_current to current, a
process accessing current will see X or Y, but never a
file-not-found or other error condition. This is sufficient to
atomically switch user environments. */
if (rename(tmp.c_str(), link.c_str()) != 0)
throw SysError(format("renaming `%1%' to `%2%'") % tmp % link);
}