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`build.zig.zon` named `../05-zig-p4` as a path dependency, and `build.zig`
`@import`ed it inside `if (-Desp32p4-firmware)`. But `@import` in a build script
is resolved when the SCRIPT is compiled, not when the branch that needs it is
taken -- so naming the package at all meant anyone without that sibling checkout
could not build pardes AT ALL. Not the firmware: the terminal shell, the SDL
shell, the tests. `zig build` failed with
build.zig:1073: error: no module named 'zig_p4' available within module 'root.@build'
from a line inside an `if` that was false.
Neither escape hatch works for a PATH dependency, and both were tried rather
than assumed. `.lazy = true` is about FETCHING; a path dep whose directory is
absent is generated as a package with no `build.zig` rather than one marked
unavailable, so `b.lazyImport` -- which exists for exactly this and is what the
standard library says is to `@import` what `lazyDependency` is to `dependency`
-- reaches a `@compileError` instead of returning null. Making it a fetched
dependency instead is not available either: the toolchain has no remote.
So the duplicate goes. That build tree's firmware block linked an image the
toolchain repository already knows how to link -- its own build.zig has
`-Dpardes`, `-Dapp=<root>` and `-Dpardes-obj=<path>`, and its comments record
having learned this same lesson from the other direction, where nesting pardes's
~30-package graph under it broke every build there. The object is the seam: it
crosses by PATH and never by package, and each repository builds what it owns
the pieces of.
zig build -Dplatform=esp32p4 # here, no toolchain needed
zig build -Dpardes # there, the console image
zig build -Dpardes -Dapp=<pardes>/src/esp32p4_9p.zig # there, the 9P image
For the second and third to work with no module map, `src/board9p.zig` and the
9P firmware root now reach the codec by PATH instead of through a named `ninep`
module that only pardes's own build.zig knew to inject -- which is also why the
root moved from `src/esp32p4/nine.zig` up to `src/esp32p4_9p.zig`, beside
`src/esp32p4.zig`: a path import may not escape its module's own directory. Both
files are now self-contained, and `zig test src/board9p.zig` works with no flags.
`-Desp32p4-port`, `-Desp32p4-prof` and `-Desp32p4-cpu-mhz` go with the block. An
option this build cannot honour is worse than no option, because it accepts the
flag and then ignores it; all three are spelled the same way in the toolchain.
Verified by moving ../05-zig-p4 out of the way: `zig build`, `zig build
-Dplatform=esp32p4` and `zig build unit-test` all pass without it. With it back,
the toolchain still links both images -- console 812,720 B, 9P 88,096 B.
next-steps.txt gains the six features the 9P chain shipped.
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Step 4 of the 9P chain (docs/9p.typ 12.4, docs/registry.typ 9P-15/16/17/4/5).
src/9p.zig is a base 9P2000 codec and a SANS-IO server: it never touches a
descriptor, takes no allocator, starts no thread, and builds for
wasm32-freestanding and riscv32-freestanding. That is what lets the same code
serve a unix socket here and a UART on the board later.
Server(comptime fs: type) duck-typed on fs.Req/fs.Reply/fs.Reply.Attr, so it
never imports acmefs and acmefs never learns 9P
init{ in, out, root } the caller owns the buffers; msize is derived
retry/next/reply the three fs_service.Transport ops, by name
push/output/wrote/hangup bytes in, bytes out, partial writes supported
next() is a PUMP, not one-message-one-request: a 3-element Twalk is three
lookups, Topen|OTRUNC is a setattr then an open, Tversion is none at all.
Decisions that were open and are now taken, each recorded in the file:
* qid.version is ALWAYS 0, which makes Linux set P9L_DIRECT and skip its
cache -- the 9P equivalent of the FOPEN_DIRECT_IO fuse.zig relies on.
* Every Rread is clamped to the client's count. An over-long one is a hard
-EIO in Linux, not a truncation.
* Rerror carries Linux's exact strerror text (registry 9P-4 option A), so a
mount recovers the errno instead of ESERVERFAULT. Asserted as literals,
because a typo there is 'Unknown error 526' on every mount.
* `.` and `..` are resolved BY THE SERVER. Under FUSE the kernel does it
and acmefs says so; 9P has no kernel, and forwarding `..` as a lookup
would break every client that normalises a path.
* Topen checks the perm bits itself. Under FUSE the kernel enforced them;
over 9P nobody is above the server, and `errors` would have been readable.
* Tcreate and Tremove are Rerror: `new/` creates a pane on WALK, so the
capability exists and is not spelled Tcreate.
THE INTEGRATION BUG, which was not in the protocol: the daemon's push_fs_reply
sent every reply to the FUSE mount, whose park table has no 9P tag, so it
dropped it -- Tversion worked (no core involved) and Tattach hung forever. That
is exactly the 'no routing origin for the 9P descriptor' cell in the layering
table of docs/9p.typ. Session.fs_origin now carries the transport that asked.
Proved with plan9port against a live daemon serving BOTH transports at once:
9p ls / and /1, read index/ctl/tag, write /1/body, stat, a walk through
/1/../index, pane creation through `new/body`, and the two refusals arriving as
strings -- 'permission denied' and 'No such file or directory' -- confirmed on
the raw wire as Rerror text rather than numbers. A write over 9P reads back
through FUSE and a write through FUSE reads back over 9P.
msize 8192, 34,072 bytes per connection (Server 9,488 + in 8,192 + out 16,384,
out being two msize so that every reply is infallible), four connections.
zig build unit-test: 468 tests before, 503 after.
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