Re: misc/io-errors fails on Alpine Linux

[Collin Funk]

Bruno Haible <br...@clisp.org> writes:

> So, if I understand it correctly:
>   - glibc     considers /dev/full to be non-interactive,
>   - musl libc considers /dev/full to be interactive.
>
> Can you show (via 'strace') the system calls related to fd = 1,
> that make this determination, in the two cases?

Well, musl does perform the check and sees it isn't a tty. However, it
still doesn't buffer the output. Here is a test program:

    $ cat main.c
    #include <stdio.h>
    #include <unistd.h>
    int
    main (void)
    {
      printf ("%s %s\n", "hello", "1");
      sleep (1);
      printf ("%s %s\n", "hello", "2");
      return 0;
    }

Here is it running on musl (trimming some obviously irrelevant calls
like brk and mmap):

    $ gcc main.c && strace ./a.out  > /dev/full
    [...]
    ioctl(1, TIOCGWINSZ, 0xbf9d08e8)        = -1 ENOTTY (Not a tty)
    writev(1, [{iov_base="hello 1", iov_len=7}, {iov_base="\n", iov_len=1}], 2) 
= -1 ENOSPC (No space left on device)
    nanosleep({tv_sec=1, tv_nsec=0}, 0xbf9d0ae0) = 0
    writev(1, [{iov_base="hello 2\n", iov_len=8}, {iov_base=NULL, iov_len=0}], 
2) = -1 ENOSPC (No space left on device)
    exit_group(0)                           = ?
    +++ exited with 0 +++

And on glibc:

    $ gcc main.c && strace ./a.out  > /dev/full
    [...]
    fstat(1, {st_mode=S_IFCHR|0666, st_rdev=makedev(0x1, 0x7), ...}) = 0
    ioctl(1, TCGETS2, 0x7ffdad7df420)       = -1 ENOTTY (Inappropriate ioctl 
for device)
    brk(NULL)                               = 0x1c9d9000
    brk(0x1c9fb000)                         = 0x1c9fb000
    clock_nanosleep(CLOCK_REALTIME, 0, {tv_sec=1, tv_nsec=0}, 0x7ffdad7df7f0) = 0
    write(1, "hello 1\nhello 2\n", 16)      = -1 ENOSPC (No space left on 
device)
    exit_group(0)                           = ?
    +++ exited with 0 +++

So both use isatty (implemented through differing, but reasonable
ioctls) and see that standard output isn't a terminal.

Collin