fuse: add host FD passthrough for external FUSE servers#13426
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manninglucas wants to merge 1 commit into
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fuse: add host FD passthrough for external FUSE servers#13426manninglucas wants to merge 1 commit into
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When a FUSE filesystem is mounted with an fd that is a host file descriptor (imported via fdimport) rather than an in-sandbox /dev/fuse DeviceFD, use a new host passthrough connection that reads and writes FUSE protocol messages directly to the host FD. This enables a FUSE server running outside the sandbox to serve filesystem requests for processes inside the sandbox. The sentry detects the host FD via a HostFD() interface check in GetFilesystem, creates a hostConnection that performs synchronous I/O over the FD, and routes all FUSE Call/CallAsync operations through it. Changes: - Add hostConnection type with synchronous Call/CallAsync/InitSend over a host FD (pkg/sentry/fsimpl/fuse/host_connection.go) - Add fuseCall/fuseCallAsync dispatch methods to filesystem that route to hostConn when set, falling back to the existing queue-based connection - Detect host FDs in GetFilesystem via a HostFD() interface and branch to getFilesystemHostFD which creates the host connection and performs FUSE_INIT synchronously - Add HostFD() method to host.fileDescription - Add unit tests using socketpair-based mock FUSE servers - Add integration tests with a full FUSE protocol server backed by a real host directory (INIT, LOOKUP, OPEN, READ, WRITE) - Add fuse_host test runner binary, --fuse-host runner flag, add_fuse_host defs.bzl support, and C++ syscall tests
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Summary
hostConnectiontype that performs synchronous FUSE protocol I/O over a host file descriptor, enabling FUSE servers running outside the sandbox to serve filesystem requests for processes insideGetFilesystemvia aHostFD()interface check and branch to a newgetFilesystemHostFDpath that creates the host connection and performsFUSE_INITsynchronouslyCall/CallAsyncoperations throughfuseCall/fuseCallAsyncdispatch methods onfilesystemthat forward tohostConnwhen setTest plan
host_connection_test.go): basic echo call, FUSE_INIT handshake, async call, not-connected error — all using socketpair-based mock servershost_connection_integration_test.go): full FUSE protocol lifecycle (INIT → LOOKUP → OPEN → READ → RELEASE and WRITE → verify backing file) with a real temp directory-backed FUSE serverfuse_host.cc):StatRoot,ReadFile,WriteAndReadBack— exercised via the_fuse_hosttest runner variant with host-sidefuse_hostserver binary🤖 Generated with Claude Code