Re: [BUG] reading from FIFO broken

Herbert Xu <[email protected]> wrote:
> Martijn Dekker <[email protected]> wrote:
>>
>> ...reading from a FIFO is broken, at least on macOS 12.7.5. It seems like the 
>> 'read' command can no longer read anything from a FIFO.
>> 
>> Reproducer:
>> 
>> $ dash -c 'trap "rm fifo" 0; mkfifo fifo;
>>        echo OK >fifo & read r <fifo; echo "${#r}:$r"'
>> 0:
>> 
>> Expected output:
>> 
>> 2:OK
> 
> I can't reproduce this under Linux.  Could you please run it under
> strace for me?

I even tried stubbing out the tee call and replacing it with

	err = -1;

and it still worked with your test case.  This is what I see through
strace on Linux with a stubbed out tee call:

395516 <... close resumed>)             = 0
395516 ioctl(0, TCGETS <unfinished ...>
395517 <... write resumed>)             = 3
395516 <... ioctl resumed>, 0x7ffcf5136a50) = -1 ENOTTY (Inappropriate ioctl for device)
395517 dup2(10, 1 <unfinished ...>
395516 lseek(0, 0, SEEK_CUR <unfinished ...>
395517 <... dup2 resumed>)              = 1
395516 <... lseek resumed>)             = -1 ESPIPE (Illegal seek)
395517 close(10 <unfinished ...>
395516 pipe2( <unfinished ...>
395517 <... close resumed>)             = 0
395516 <... pipe2 resumed>[3, 4], 0)    = 0
395517 exit_group(0 <unfinished ...>
395516 fcntl(3, F_DUPFD_CLOEXEC, 10 <unfinished ...>
395517 <... exit_group resumed>)        = ?
395516 <... fcntl resumed>)             = 11
395516 close(3)                         = 0
395516 fcntl(4, F_DUPFD_CLOEXEC, 10)    = 12
395517 +++ exited with 0 +++
395516 --- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=395517, si_uid=1000, si_status=0, si_utime=0, si_stime=0} ---
395516 rt_sigreturn({mask=[]})          = 12
395516 close(4)                         = 0
395516 read(0, "O", 1)                  = 1
395516 read(0, "K", 1)                  = 1
395516 read(0, "\n", 1)                 = 1
395516 wait4(-1, [{WIFEXITED(s) && WEXITSTATUS(s) == 0}], WNOHANG, NULL) = 395517
395516 wait4(-1, 0x7ffcf5136b3c, WNOHANG, NULL) = -1 ECHILD (No child processes)
395516 dup2(10, 0)                      = 0
395516 close(10)                        = 0
395516 write(1, "2:OK\n", 5)            = 5
395516 exit_group(0)                    = ?
395516 +++ exited with 0 +++

Cheers,
-- 
Email: Herbert Xu <[email protected]>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt