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Move daemon process into sub-cgroup

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The daemon process is now moved into a new sub-cgroup called nix-daemon when the
daemon starts. This is necessary to abide by the no-processes-in-inner-nodes
rule, because the service cgroup becomes an inner node when the child cgroups
for the build are created (see LocalDerivationGoal::startBuilder()).

See #9675
This commit is contained in:
Parker Hoyes 2024-08-26 13:50:22 +00:00
parent 1073a8effa
commit 46b3188045
4 changed files with 75 additions and 12 deletions
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21
src/libstore/unix/build/local-derivation-goal.cc
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@ -444,25 +444,22 @@ void LocalDerivationGoal::startBuilder()
#if __linux__
experimentalFeatureSettings.require(Xp::Cgroups);
/* If we're running from the daemon, then this will return the
root cgroup of the service. Otherwise, it will return the
current cgroup. */
auto rootCgroup = getRootCgroup();
auto cgroupFS = getCgroupFS();
if (!cgroupFS)
throw Error("cannot determine the cgroups file system");
auto ourCgroups = getCgroups("/proc/self/cgroup");
auto ourCgroup = ourCgroups[""];
if (ourCgroup == "")
throw Error("cannot determine cgroup name from /proc/self/cgroup");
auto ourCgroupPath = canonPath(*cgroupFS + "/" + ourCgroup);
if (!pathExists(ourCgroupPath))
throw Error("expected cgroup directory '%s'", ourCgroupPath);
auto rootCgroupPath = canonPath(*cgroupFS + "/" + rootCgroup);
if (!pathExists(rootCgroupPath))
throw Error("expected cgroup directory '%s'", rootCgroupPath);
static std::atomic<unsigned int> counter{0};
cgroup = buildUser
? fmt("%s/nix-build-uid-%d", ourCgroupPath, buildUser->getUID())
: fmt("%s/nix-build-pid-%d-%d", ourCgroupPath, getpid(), counter++);
? fmt("%s/nix-build-uid-%d", rootCgroupPath, buildUser->getUID())
: fmt("%s/nix-build-pid-%d-%d", rootCgroupPath, getpid(), counter++);
debug("using cgroup '%s'", *cgroup);