Message-ID: <545A88E6.2060509@gmail.com>
Date: Wed, 05 Nov 2014 15:30:30 -0500
From: Austin S Hemmelgarn <ahferroin7@gmail.com>
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To: "Theodore Ts'o" <tytso@mit.edu>, Martin Tournoij <martin@arp242.net>,
        linux-kernel@vger.kernel.org
Subject: Re: [RFC] The SIGINFO signal from BSD
References: <1415200663.3247743.187387481.75CE9317@webmail.messagingengine.com> <545A7B00.1040309@gmail.com> <20141105201404.GH27083@thunk.org>
In-Reply-To: <20141105201404.GH27083@thunk.org>
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On 2014-11-05 15:14, Theodore Ts'o wrote:
> On Wed, Nov 05, 2014 at 02:31:12PM -0500, Austin S Hemmelgarn wrote:
>>>
>>> SIGINFO prints the status of the process to the terminal; BSD cp, for=
 example,
>>> shows show much data it's copied:
>>>
>>>      $ cp large_file /dev/null
>>>      <press ^t>
>>>      load: 1.39  cmd: cp 85837 [running] 3.91r 0.00u 0.98s 8% 2340k
>>>      large_file -> /dev/null  15%
>>>
>>> As you see, it shows the current load, pid, process status, memory us=
age, as
>>> well as how much of the file has been copied. Many other BSD tools pr=
int similar
>>> statistics (mv, tar, dd, sleep, fetch, etc.).
>>
>> You have to understand however, that the reason that SIGINFO works lik=
e that
>> on *BSD is that the kernel and core userspace are developed together,
>> whereas on Linux, they are maintained entirely separately. Outside of =
core
>> userspace components, using SIGINFO that way on *BSD is just conventio=
n.
>
> Actually, the first line:
>
> 	load: 1.39  cmd: cp 85837 [running] 3.91r 0.00u 0.98s 8% 2340k
>
> is actually printed by the kernel.  It's actually something which is
> implemented in the BSD N_TTY line displine.  We never implemented it
> (at least when I was maintaining the tty subsystem) mostly out of
> laziness.  Part of the reason is that the main reason was that main
> reason why people (at least systems programmers / kernel programers
> like me) used ^T was to debug an apparently hung system, and for
> Linux, we had a much more powerful system using the magic-sysrq key.
>
I hadn't realized that it was actually the kernel printing that, but=20
then I've never really looked all that deep into the BSD source code.
Ironically, the magic-sysrq key is one of the big reasons I've=20
personally chosen to stay with Linux over any of the BSD derivatives. :)


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