Running head on /dev/zero is … wrong. Arguably without -c it should loop forever until it crashes due to malloc() failure, or it should copy an infinite sequence of zero bytes because it never reaches a newline.
The problem is that zero is a special character (end of string) — its unclear to me what the correct behavior here should be. What happens if you embed zero bytes in a file? Note that in POSIX, head lacks -c, so the behavior is not part of any standard. I *think* the “right” answer here is that NUL should be treated like any other character, which precludes the use of normal C string handling functions in head. Even fgets(3C) and getline(3C) cannot be used. Seriously, head and copy are for use in text files, not with arbitrary binary data files, and so their handling (or mishandling) of binary data should not come as a surprise. That said, on BSD (Darwin) head -c 1 copies a single zero byte. head without -c just returns an error. (Not sure what the error is, because I can’t dtruss it in new Darwin. Thanks Apple.) - Garrett On Tue, Mar 22, 2016 at 10:19 AM, Richard PALO <rich...@netbsd.org> wrote: > What I'm seeing is an infinite loop of the following (using /usr/bin/head): > > truss -u libc head -c 1 /dev/zero > > ... > > /1@1: -> libc:fgets(0x8047680, 0x400, 0x80622b0, 0x0) > > /1: read(3, "\0\0\0\0\0\0\0\0\0\0\0\0".., 8192) = 8192 > > /1@1: <- libc:fgets() = 0x8047680 > > /1@1: -> libc:strlen() > > /1@1: <- libc:strlen() = 0 > > /1@1: -> libc:printf() > > /1@1: <- libc:printf() = 0 > > /1@1: -> libc:fflush(0x8062290, 0x8047680, 0x80622b0, 0x0) > > /1@1: <- libc:fflush() = 0 > > /1@1: -> libc:fgets(0x8047680, 0x400, 0x80622b0, 0x0) > > /1@1: <- libc:fgets() = 0x8047680 > > /1@1: -> libc:strlen() > > /1@1: <- libc:strlen() = 0 > > /1@1: -> libc:printf() > > /1@1: <- libc:printf() = 0 > > /1@1: -> libc:fflush(0x8062290, 0x8047680, 0x80622b0, 0x0) > > /1@1: <- libc:fflush() = 0 > > /1@1: -> libc:fgets(0x8047680, 0x400, 0x80622b0, 0x0) > > /1@1: <- libc:fgets() = 0x8047680 > > /1@1: -> libc:strlen() > > /1@1: <- libc:strlen() = 0 > > /1@1: -> libc:printf() > > /1@1: <- libc:printf() = 0 > > /1@1: -> libc:fflush(0x8062290, 0x8047680, 0x80622b0, 0x0) > > /1@1: <- libc:fflush() = 0 > > /1@1: -> libc:fgets(0x8047680, 0x400, 0x80622b0, 0x0) > > /1@1: <- libc:fgets() = 0x8047680 > > /1@1: -> libc:strlen() > > /1@1: <- libc:strlen() = 0 > > /1@1: -> libc:printf() > > /1@1: <- libc:printf() = 0 > > /1@1: -> libc:fflush(0x8062290, 0x8047680, 0x80622b0, 0x0) > > /1@1: <- libc:fflush() = 0 > > /1@1: -> libc:fgets(0x8047680, 0x400, 0x80622b0, 0x0) > > /1@1: <- libc:fgets() = 0x8047680 > > /1@1: -> libc:strlen() > > /1@1: <- libc:strlen() = 0 > > /1@1: -> libc:printf() > > /1@1: <- libc:printf() = 0 > > /1@1: -> libc:fflush(0x8062290, 0x8047680, 0x80622b0, 0x0) > > /1@1: <- libc:fflush() = 0 > > /1@1: -> libc:fgets(0x8047680, 0x400, 0x80622b0, 0x0) > > /1@1: <- libc:fgets() = 0x8047680 > > /1@1: -> libc:strlen() > > /1@1: <- libc:strlen() = 0 > > /1@1: -> libc:printf() > > /1@1: <- libc:printf() = 0 > > /1@1: -> libc:fflush(0x8062290, 0x8047680, 0x80622b0, 0x0) > > /1@1: <- libc:fflush() = 0 > > /1@1: -> libc:fgets(0x8047680, 0x400, 0x80622b0, 0x0) > > /1@1: <- libc:fgets() = 0x8047680 > > /1@1: -> libc:strlen() > > /1@1: <- libc:strlen() = 0 > > /1@1: -> libc:printf() > > /1@1: <- libc:printf() = 0 > > /1@1: -> libc:fflush(0x8062290, 0x8047680, 0x80622b0, 0x0) > > /1@1: <- libc:fflush() = 0 > > /1@1: -> libc:fgets(0x8047680, 0x400, 0x80622b0, 0x0) > > /1@1: <- libc:fgets() = 0x8047680 > > /1@1: -> libc:strlen() > > /1@1: <- libc:strlen() = 0 > > /1@1: -> libc:printf() > > /1@1: <- libc:printf() = 0 > > /1@1: -> libc:fflush(0x8062290, 0x8047680, 0x80622b0, 0x0) > > /1@1: <- libc:fflush() = 0 > > ... > and again and again > > -- > Richard PALO > ------------------------------------------- illumos-discuss Archives: https://www.listbox.com/member/archive/182180/=now RSS Feed: https://www.listbox.com/member/archive/rss/182180/21175430-2e6923be Modify Your Subscription: https://www.listbox.com/member/?member_id=21175430&id_secret=21175430-6a77cda4 Powered by Listbox: http://www.listbox.com
