1 files changed, 57 insertions, 0 deletions
diff --git a/src/nix-env/profiles.cc b/src/nix-env/profiles.cc
new file mode 100644
index 000000000000..5b9c004066b5
--- /dev/null
+++ b/src/nix-env/profiles.cc
@@ -0,0 +1,57 @@
+#include "profiles.hh"
+
+
+Path createGeneration(Path profile, Path outPath, Path drvPath)
+{
+    Path profileDir = dirOf(profile);
+    string profileName = baseNameOf(profile);
+    
+    unsigned int num = 0;
+    
+    Strings names = readDirectory(profileDir);
+    for (Strings::iterator i = names.begin(); i != names.end(); ++i) {
+        if (string(*i, 0, profileName.size() + 1) != profileName + "-") continue;
+        string s = string(*i, profileName.size() + 1);
+        int p = s.find("-link");
+        if (p == string::npos) continue;
+        istringstream str(string(s, 0, p));
+        unsigned int n;
+        if (str >> n && str.eof() && n >= num) num = n + 1;
+    }
+
+    Path generation, gcrootSrc;
+
+    while (1) {
+        Path prefix = (format("%1%-%2%") % profile % num).str();
+        generation = prefix + "-link";
+        gcrootSrc = prefix + "-src.gcroot";
+        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(gcrootSrc, drvPath);
+
+    return generation;
+}
+
+
+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);
+}