Raise host NOFILE capacity for the guest FD table#204
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elfuse exposes a 1024-entry guest FD table but currently inherits the host RLIMIT_NOFILE unchanged. With a host soft limit of 256, guests hit host-side EMFILE after opening 248 additional descriptors and test-stress fails deterministically. Ensure the top-level elfuse process has capacity for FD_TABLE_SIZE plus 64 descriptors reserved for runtime-owned pipes, fork IPC, debugger sockets, and sysroot/FUSE plumbing. Preserve the host hard limit and report a startup error when the required capacity cannot be established. Fork helpers inherit the capacity established by the top-level process and do not reapply the startup policy after a guest may have changed RLIMIT_NOFILE.
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Keep the host descriptor reserve internal by serving guest NOFILE queries and updates from a guest-side 1024/1024 limit. Guest setrlimit no longer lowers the host capacity that elfuse needs for runtime and fork IPC. Carry the guest limit through the fork protocol, restore inherited descriptors before applying a lowered soft limit, and recheck host capacity in fork helpers. Add regressions for hidden reserve reporting and fork after lowering the hard limit. PR sysprog21#148 addresses the same low-host-limit failure with a different startup policy and a host-side regression wrapper. Close sysprog21#68
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Problem
elfuse exposes a guest FD table with 1024 entries, but the host process may start with a much smaller soft RLIMIT_NOFILE. On a host soft limit of 256, the stress test can open only about 248 guest descriptors before the host runs out of descriptors, even though the guest table still has capacity.
Host capacity and guest-visible NOFILE state also need to remain separate: exposing the internal reserve reports an unreachable limit, while forwarding guest setrlimit to the host can remove capacity needed by fork IPC.
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Related work
PR #148 addresses the same issue by raising the host limit in fdtable initialization and adding a host-side low-limit regression wrapper. This PR also separates guest-visible NOFILE state from elfuse internal host capacity and preserves that state across fork IPC.
Close #68