Enable lazy/sparse allocation of generation symlinks: avoid creating
new generations if a generation already exists. Alternatively or additionally I propose a mode where only the *last* generation will be sparse.
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@ -80,7 +80,22 @@ Path createGeneration(Path profile, Path outPath)
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previous ones. */
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previous ones. */
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int dummy;
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int dummy;
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Generations gens = findGenerations(profile, dummy);
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Generations gens = findGenerations(profile, dummy);
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unsigned int num = gens.size() > 0 ? gens.back().number : 0;
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unsigned int num;
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if (gens.size() > 0) {
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/* Check existing generations whether they represent an
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environment we already materialized before. In that case:
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avoid cluttering the system with additional symlinks. */
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for (auto & gen : gens) {
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if (readLink(gen.path) == outPath) {
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return gen.path;
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}
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}
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num = gens.back().number;
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} else {
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num = 0;
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}
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/* Create the new generation. Note that addPermRoot() blocks if
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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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the garbage collector is running to prevent the stuff we've
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@ -99,6 +99,15 @@ if nix-env -q '*' | grep -q bar; then false; fi
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nix-env --list-generations
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nix-env --list-generations
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test "$(nix-env --list-generations | wc -l)" -eq 7
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test "$(nix-env --list-generations | wc -l)" -eq 7
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# Doing the same operation twice should result in the same generation, not an
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# additional one. At this point we just brought back foo. Installing it again
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# should not create a new generation.
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nix-env -i foo
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# Count generations.
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nix-env --list-generations
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test "$(nix-env --list-generations | wc -l)" -eq 7
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# Switch to a specified generation.
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# Switch to a specified generation.
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nix-env --switch-generation 7
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nix-env --switch-generation 7
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[ "$(nix-store -q --resolve $profiles/test)" = "$oldGen" ]
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[ "$(nix-store -q --resolve $profiles/test)" = "$oldGen" ]
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