daemonize: use an allow-list approach to inherited FDs - #2841
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sylvestre merged 1 commit intoSep 11, 2026
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Our current approach is to try and close the jobserver file descriptors inherited from make, using heuristics based on parsing the MAKEFLAGS searching for explicit FD numbers. However, in some circumstances, make will dup() those file descriptors internally, and we'll inherit and leak those duplicated FDs, which can lead to build script deadlocking. This happens to me frequently when working on Firefox on my macOS machine: when I run `./mach lint --outgoing` with substantial Rust work, once the clippy run ends, `make` idles waiting for job tokens to be handed back through those open file descriptors, until the daemonized server finally finishes through its idle timeout, closing their end of the pipes. So, instead of trying to pinpoint what must absolutely be closed, we take the opposite approach, and assume that most file descriptors don't need to be inherited when spawning a daemon.
Codecov Report❌ Patch coverage is
Additional details and impacted files@@ Coverage Diff @@
## main #2841 +/- ##
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+ Coverage 73.84% 75.91% +2.06%
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Files 72 72
Lines 38178 39384 +1206
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+ Hits 28194 29899 +1705
+ Misses 9984 9485 -499 ☔ View full report in Codecov by Harness. 🚀 New features to boost your workflow:
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Our current approach is to try and close the jobserver file descriptors inherited from make, using heuristics based on parsing the MAKEFLAGS searching for explicit FD numbers. However, in some circumstances, make will dup() those file descriptors internally, and we'll inherit and leak those duplicated FDs, which can lead to build script deadlocking.
This happens to me frequently when working on Firefox on my macOS machine: when I run
./mach lint --outgoingwith substantial Rust work, once the clippy run ends,makeidles waiting for job tokens to be handed back through those open file descriptors, until the daemonized server finally finishes through its idle timeout, closing their end of the pipes.So, instead of trying to pinpoint what must absolutely be closed, we take the opposite approach, and assume that most file descriptors don't need to be inherited when spawning a daemon.