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Enable lazy/sparse allocation of generation symlinks: avoid creating

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new generations if a generation already exists.

Alternatively or additionally I propose a mode where only the *last* generation will be sparse.
This commit is contained in:
Christian Theune 2015-05-18 08:38:49 +02:00
parent be1ff23352
commit 3d83188702
2 changed files with 25 additions and 1 deletions
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17
src/nix-env/profiles.cc
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@ -80,7 +80,22 @@ Path createGeneration(Path profile, Path outPath)
previous ones. */
int dummy;
Generations gens = findGenerations(profile, dummy);
unsigned int num = gens.size() > 0 ? gens.back().number : 0;
unsigned int num;
if (gens.size() > 0) {
/* Check existing generations whether they represent an
environment we already materialized before. In that case:
avoid cluttering the system with additional symlinks. */
for (auto & gen : gens) {
if (readLink(gen.path) == outPath) {
return gen.path;
}
}
num = gens.back().number;
} else {
num = 0;
}
/* Create the new generation. Note that addPermRoot() blocks if
the garbage collector is running to prevent the stuff we've

9
tests/user-envs.sh
View file

@ -99,6 +99,15 @@ if nix-env -q '*' | grep -q bar; then false; fi
nix-env --list-generations
test "$(nix-env --list-generations | wc -l)" -eq 7
# Doing the same operation twice should result in the same generation, not an
# additional one. At this point we just brought back foo. Installing it again
# should not create a new generation.
nix-env -i foo
# Count generations.
nix-env --list-generations
test "$(nix-env --list-generations | wc -l)" -eq 7
# Switch to a specified generation.
nix-env --switch-generation 7
[ "$(nix-store -q --resolve $profiles/test)" = "$oldGen" ]