secret_file_open() opened secret files with O_NONBLOCK and only cleared it
for S_ISREG, so on a FIFO/process-substitution source (--password-file
<(...), --early-input <(...)) fgets() failed immediately with EAGAIN when
the writer had not yet produced data, breaking slow producers.
Keep O_NONBLOCK at open() (a writer-less FIFO must not block the open) and
route all three readers through a new secret_read_line() helper. It
accumulates a line across reads and, on EAGAIN/EWOULDBLOCK (or a partial
line) with no newline and no EOF, clearerr()s and polls for readability
against one overall CLOCK_MONOTONIC deadline of
CREDENTIAL_FIFO_READ_TIMEOUT_MS (3000 ms); on timeout or a real read error
it fails with a clear message. EOF finishes normally. Regular files are
left blocking and read exactly as before.
Handles a line split across several write()s and keeps the owner/mode
fstat gate, O_NOFOLLOW and the /dev/fd/N exception unchanged.
TapTap
9f47b13712