58 lines
2.0 KiB
C++
58 lines
2.0 KiB
C++
#include "profiles.hh"
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Path createGeneration(Path profile, Path outPath, Path drvPath)
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{
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Path profileDir = dirOf(profile);
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string profileName = baseNameOf(profile);
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unsigned int num = 0;
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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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if (string(*i, 0, profileName.size() + 1) != profileName + "-") continue;
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string s = string(*i, profileName.size() + 1);
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int p = s.find("-link");
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if (p == string::npos) continue;
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istringstream str(string(s, 0, p));
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unsigned int n;
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if (str >> n && str.eof() && n >= num) num = n + 1;
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}
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Path generation, gcrootSrc;
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while (1) {
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Path prefix = (format("%1%-%2%") % profile % num).str();
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generation = prefix + "-link";
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gcrootSrc = prefix + "-src.gcroot";
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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(gcrootSrc, drvPath);
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return 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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