64-@@ gdb /drv/e/grep/b3.1/src/grep
GNU gdb (GDB) (Cygwin 7.12.1-2) 7.12.1
...

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Reading symbols from /drv/e/grep/b3.1/src/grep...done.
(gdb) set args .
(gdb) br main
Breakpoint 1 at 0x10040419a: file ../../grep-3.1/src/grep.c, line 2415.
(gdb) br reset
Breakpoint 2 at 0x1004032bc: file ../../grep-3.1/src/grep.c, line 847.
(gdb) br grep.c:856 <==== break-point on "if (seek_failed)" in grep.c/reset()
Breakpoint 3 at 0x100403850: file ../../grep-3.1/src/grep.c, line 856.
(gdb) run
Starting program: /drv/e/grep/b3.1/src/grep .
[New Thread 4684.0xe28]
[New Thread 4684.0x834]

Thread 1 hit Breakpoint 1, main (argc=2, argv=0xffffcc40) at ../../grep-3.1/src/grep.c:2415
2415    {
(gdb) p dup2(open("fifo", 0), 0) # make stdin refer to the fifo ...
<GDB does not return because the open() call blocks>

    Using another terminal, execute: echo aaa > fifo (open() for write resumes the open() call above)

$1 = 0
(gdb) cont
Continuing.

Thread 1 hit Breakpoint 2, grep (ineof=<synthetic pointer>, st=0xffffc940, fd=0) at ../../grep-3.1/src/grep.c:1447
1447      if (! reset (fd, st))
(gdb) cont
Continuing.

Thread 1 hit Breakpoint 3, reset (st=0xffffc940, fd=0) at ../../grep-3.1/src/grep.c:856
856       if (seek_failed)
(gdb) p seek_failed
$2 = true
(gdb) p bufoffset
$3 = -1
(gdb) p errno
$4 = 22           # EINVAL, because NT returns ERROR_INVALID_PARAMETER (= 87)
(gdb) p errno=29  # replace w/ ESPIPE (= illegal seek)
$5 = 29
(gdb) cont
Continuing.
aaa               # output of grep as expected/desired
[Inferior 1 (process 4684) exited normally]
(gdb) quit
64-@@ 

Q: why is the fifo not recognized as a pipe by Cygwin? (why does Linux recognize it a fifo/pipe?)

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