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st: chunked pread with EINTR retry and honest short-read errors

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Two latent bugs in every st.h reader, both hit in the field:

 - a single pread caps at ~2^31 bytes on Linux, so any tensor past
   2.1 GB (bf16 embed/unembed tensors of large models qualify) came
   back silently truncated with perror printing '... : Success'
   (errno untouched by a short read) — the same misleading-error
   symptom glm.c fixed for its own reads in #236;
 - no EINTR retry.

st_pread_full loops in ST_PREAD_CHUNK pieces (1 GB default, override
for tests), retries EINTR, and reports offset + progress on failure.
All five read sites converted; behavior on well-formed files is
byte-identical (GLM oracle re-verified on this branch: 32/32).

tests/test_st_pread builds with -DST_PREAD_CHUNK=7 so a 96-byte tensor
exercises the multi-chunk loop, and forks a child against a shard
truncated after st_init (init's static bounds check means the pread
path only fires when a file shrinks under a live handle) asserting
exit(1) with a 'short read' message and no 'Success'.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
This commit is contained in:
Nicholas Beerbower
2026-07-16 15:20:43 -04:00
parent d45cfa268a
commit 6507817d9f
3 changed files with 117 additions and 6 deletions
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c/Makefile
+4 -1
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@@ -166,7 +166,7 @@ else
PYTHON ?= python3
endif
CUDA_OBJ =
TEST_BINS = tests/test_json$(EXE) tests/test_st$(EXE) tests/test_tier$(EXE) tests/test_grammar$(EXE) tests/test_schema_gbnf$(EXE) tests/test_decode_batch$(EXE) tests/test_idot$(EXE) tests/test_i4_grouped$(EXE) tests/test_stops$(EXE) tests/test_kv_alloc$(EXE) tests/test_i4_acc512$(EXE) tests/test_compat_direct$(EXE)
TEST_BINS = tests/test_json$(EXE) tests/test_st$(EXE) tests/test_st_pread$(EXE) tests/test_tier$(EXE) tests/test_grammar$(EXE) tests/test_schema_gbnf$(EXE) tests/test_decode_batch$(EXE) tests/test_idot$(EXE) tests/test_i4_grouped$(EXE) tests/test_stops$(EXE) tests/test_kv_alloc$(EXE) tests/test_i4_acc512$(EXE) tests/test_compat_direct$(EXE)
ifneq (,$(LINUX))
TEST_BINS += tests/test_uring$(EXE)
endif
@@ -293,6 +293,9 @@ iobench$(EXE): iobench.c compat.h
tests/test_json$(EXE): tests/test_json.c json.h
$(CC) $(CFLAGS) $< -o $@ $(LDFLAGS)
tests/test_st_pread$(EXE): tests/test_st_pread.c st.h json.h compat.h
$(CC) $(CFLAGS) -DST_PREAD_CHUNK=7 $< -o $@ $(LDFLAGS)
tests/test_st$(EXE): tests/test_st.c st.h json.h compat.h
$(CC) $(CFLAGS) $< -o $@ $(LDFLAGS)