squashfuse - #172
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Adds a fuse-based alternative to the setuid kernel squashfs mount: a per-task rootless user-namespace sandbox (src/uenv/rootless.cpp) that mounts images via squashfuse's low-level API, namespace-join infrastructure (src/uenv/ns_join.*) so that only one task per node performs the mount and the rest join its namespaces, and a dedicated Slurm SPANK plugin path (src/slurm/plugin_fuse.cpp) selected at build time via the new `fuse`/`fuse_version` meson options. squashfs-mount now dispatches between the setuid/kernel and rootless/fuse implementations through a small setup/mount/exit hook seam. Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
bcumming
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Aug 18, 2026
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| #include "util/expected.h" | ||
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| namespace uenv { |
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These wrappers for openat and write would go into src/util.
However, they are used in one location (rootless.cpp), so you could define them in an anonymous namespace at the top of that file.
| #include <util/expected.h> | ||
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| // timeout in seconds for waiting for join semaphore. | ||
| #define JOIN_TIMEOUT 30 |
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use constexpr, e.g. consexpr int join_timeout=30;
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| #include "ns_join.h" | |||
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The ns_join.* files could probably go into src/util and be in their own C++ namespace,
| namespace uenv { | ||
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| /* Variables for coordinating join */ | ||
| struct join_t { |
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This can probably be PIMPLed, so that the interface does not leak all the implementation (i.e. end users probably won't need the pointer to the semaphore)
| assert_line --partial "error: unable to create repository" | ||
| assert_line --partial "Permission denied" | ||
| # root ignores directory permissions, so skip this subtest when running as root | ||
| if [[ "$(id -u)" -ne 0 ]]; then |
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Tests should not be run as root, so I think we can skip this.
do_sqfs_ll_mount hand-rolled a pipe()/fork()/read()/write() dance to let the parent block until the forked squashfuse daemon signals it has mounted. Pull that into a small, independently unit-tested class in src/util/, leaving the squashfuse-specific child body untouched. Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
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This reverts commit fc48b12.
…ter jobs - if any
daemon outlasts all processes
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add rootless FUSE mounting backend with multi-task --join support
Adds -Dmount_backend=fuse as an unprivileged alternative to the setuid
kernel backend, using squashfuse in a user+mount namespace. Includes
uenv run/start --join, which lets multiple Slurm tasks on a node share
one mount via a leader-election rendezvous (src/util/proc_barrier.*).
Hardened via torture testing on Alps: mount lifetime is now owned by a
supervisor reaped with the Slurm step's cgroup rather than tied to an
arbitrary rank's command, followers keep their working directory across
setns(), and shared-memory/mutex teardown fails closed under fault
injection.