Re: [Caml-list] Re: Unix.getlogin () fails when stdin is redirected

[Till Varoquaux <till@pps.jussieu.fr>]

getpwuid(getuid()) is not a synonym for get_login (refer to the
discussion in the POSIX standard[^1]). You should not shadow posix
functions by functions with different semantics in the Unix modules;
providing your own abstraction over the OS is a commendable goal but
you should do so without silently bypassing core functions.

Till
[1]:http://pubs.opengroup.org/onlinepubs/007904975/functions/getlogin.html


On Tue, Mar 20, 2012 at 2:28 PM, David House <dhouse@janestreet.com> wrote:
> Note that Jane Street's core library [1] does not use getlogin(3) in its
> replacement Unix module, for exactly this reason:
>
> (* The standard getlogin function goes through utmp which is unreliable,
>  see the BUGS section of getlogin(3) *)
> let getlogin_orig = Unix.getlogin
> let getlogin () = (Unix.getpwuid (getuid ())).Unix.pw_name
>
> [1]: https://bitbucket.org/yminsky/ocaml-core/wiki/Home
>
> I just tested your specific example, and it worked fine.
>
>
> On Tue 20 Mar 2012 06:07:59 PM GMT, Ricardo Catalinas Jiménez wrote:
>>
>> On Tue, Mar 20, 2012 at 06:51:13PM +0100, Ricardo Catalinas Jiménez wrote:
>>>
>>> I found out the next issue in this simple code:
>>>
>>> let () =
>>>     print_endline "Hello";
>>>     print_endline (Unix.getlogin ())
>>>
>>> Running in the normal case, with `./a.out' gives:
>>>
>>> Hello
>>> ricardo
>>>
>>> But running like `./a.out</dev/null' makes Unix.getlogin fail:
>>>
>>> Hello
>>> Fatal error: exception Unix.Unix_error(20, "getlogin", "")
>>>
>>> A simple strace reveals the problem:
>>>
>>>    open("/etc/passwd", O_RDONLY|O_CLOEXEC) = 3
>>>    fstat(3, {st_mode=S_IFREG|0644, st_size=509, ...}) = 0
>>>    mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1,
>>> 0) = 0x7fb125554000
>>>    read(3, "root:x:0:0:root:/root:/bin/bash\n"..., 4096) = 509
>>>    read(3, "", 4096)                       = 0
>>>    close(3)                                = 0
>>>    munmap(0x7fb125554000, 4096)            = 0
>>> ->  ioctl(0, SNDCTL_TMR_TIMEBASE or SNDRV_TIMER_IOCTL_NEXT_DEVICE or
>>> TCGETS, 0x7fff12682c98) = -1 ENOTTY (Inappropriate ioctl for device)
>>>    write(2, "Fatal error: exception Unix.Unix"..., 59) = 59
>>>    exit_group(2)                           = ?
>>
>>
>>
>> Someone knew the answer, man 3 getlogin reads:
>>
>>        Note that glibc does not follow the POSIX specification and uses
>>        stdin instead of /dev/tty.  A bug.  (Other recent systems, like
>>        SunOS 5.8 and HP-UX 11.11 and FreeBSD 4.8 all return the login
>>        name also when stdin is redirected.)
>>
>>
>> Regards
>
>
>
>
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