Re: [sot] file times / file metadata

From	"Pascal J. Bourguignon" <pjb@informatimago.com>
Newsgroups	comp.lang.c
Subject	Re: [sot] file times / file metadata
Date	2017-11-22 17:11 +0100
Organization	Informatimago
Message-ID	<m2bmjucmyw.fsf@informatimago.com> (permalink)
References	(2 earlier) <d345c604-951c-4f3b-b189-7b41bad1d8e0@googlegroups.com> <eae94c1a-9e49-409a-8cfa-3683ce05082a@googlegroups.com> <m23757e43g.fsf@informatimago.com> <ov3i8h$t7m$1@dont-email.me> <ov40l4$287$1@jstuckle.eternal-september.org>

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Jerry Stuckle <jstucklex@attglobal.net> writes:

> On 11/22/2017 5:07 AM, David Brown wrote:
>> On 21/11/17 22:04, Pascal J. Bourguignon wrote:
>>> fir <profesor.fir@gmail.com> writes:
>>>
>>>> note yet i made some test that was
>>>> copyying file in total comender and the result is a bit discussable
>>>>
>>>>
>>>> - when i copied file the old one file changed acces time to current
>>>> (though i was not opening it only copying)
>>>
>>> Think about it!
>>>
>>> How would YOU copy the file if not by opening it and reading it?
>>>
>>> (There is  an answer, and once  you find it, you'll  understand why it's
>>> not provided, and why you have to open the file and read it to copy it).
>>>
>>
>> I can think of ways to copy a file without reading it.  In fact, I
>> regularly make copies of my entire filesystems without reading them.
>>
>>
>
> I would love to see how you copy a file or filesystem without reading it.

Well, the cheat was that I used "reading" as read(2).  The kernel could
implement a copy(2) syscall that would still read the blocks for the
file, but not by open(2)ing the file and read(2)ing it, but instead by
calling the kernel internals to read the blocks listed in the inode and
duplicate them.

For example, the naive user space implementation (using read(2)) would
unsparse sparse files, while the naive kernel implementation
(duplicating inode and blocks) would keep sparseness.

-- 
__Pascal J. Bourguignon
http://www.informatimago.com

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[sot] file times / file metadata fir <profesor.fir@gmail.com> - 2017-11-21 11:50 -0800
  Re: [sot] file times / file metadata "Pascal J. Bourguignon" <pjb@informatimago.com> - 2017-11-21 21:05 +0100
    Re: [sot] file times / file metadata Ian Collins <ian-news@hotmail.com> - 2017-11-22 09:15 +1300
    Re: [sot] file times / file metadata fir <profesor.fir@gmail.com> - 2017-11-21 12:23 -0800
      Re: [sot] file times / file metadata fir <profesor.fir@gmail.com> - 2017-11-21 12:42 -0800
        Re: [sot] file times / file metadata fir <profesor.fir@gmail.com> - 2017-11-21 13:01 -0800
        Re: [sot] file times / file metadata "Pascal J. Bourguignon" <pjb@informatimago.com> - 2017-11-21 22:04 +0100
          Re: [sot] file times / file metadata fir <profesor.fir@gmail.com> - 2017-11-21 13:17 -0800
          Re: [sot] file times / file metadata fir <profesor.fir@gmail.com> - 2017-11-21 13:22 -0800
            Re: [sot] file times / file metadata "Pascal J. Bourguignon" <pjb@informatimago.com> - 2017-11-21 23:23 +0100
              Re: [sot] file times / file metadata Ian Collins <ian-news@hotmail.com> - 2017-11-22 11:34 +1300
              Re: [sot] file times / file metadata Lew Pitcher <lew.pitcher@digitalfreehold.ca> - 2017-11-21 17:34 -0500
              Re: [sot] file times / file metadata fir <profesor.fir@gmail.com> - 2017-11-21 16:16 -0800
                Re: [sot] file times / file metadata "Pascal J. Bourguignon" <pjb@informatimago.com> - 2017-11-22 01:44 +0100
                Re: [sot] file times / file metadata Ian Collins <ian-news@hotmail.com> - 2017-11-22 14:10 +1300
                Re: [sot] file times / file metadata gordonb.eiy78@burditt.org (Gordon Burditt) - 2017-11-28 01:55 -0600
          Re: [sot] file times / file metadata David Brown <david.brown@hesbynett.no> - 2017-11-22 11:07 +0100
            Re: [sot] file times / file metadata Jerry Stuckle <jstucklex@attglobal.net> - 2017-11-22 09:13 -0500
              Re: [sot] file times / file metadata David Brown <david.brown@hesbynett.no> - 2017-11-22 15:50 +0100
                Re: [sot] file times / file metadata jameskuyper@verizon.net - 2017-11-22 07:08 -0800
                Re: [sot] file times / file metadata David Brown <david.brown@hesbynett.no> - 2017-11-22 16:22 +0100
                Re: [sot] file times / file metadata bartc <bc@freeuk.com> - 2017-11-22 15:37 +0000
                Re: [sot] file times / file metadata bartc <bc@freeuk.com> - 2017-11-22 15:43 +0000
                Re: [sot] file times / file metadata Jerry Stuckle <jstucklex@attglobal.net> - 2017-11-22 15:01 -0500
                Re: [sot] file times / file metadata Ian Collins <ian-news@hotmail.com> - 2017-11-23 17:52 +1300
                Re: [sot] file times / file metadata Jerry Stuckle <jstucklex@attglobal.net> - 2017-11-23 14:12 -0500
                Re: [sot] file times / file metadata Ian Collins <ian-news@hotmail.com> - 2017-11-24 08:28 +1300
                Re: [sot] file times / file metadata Jerry Stuckle <jstucklex@attglobal.net> - 2017-11-24 08:52 -0500
                Re: [sot] file times / file metadata David Brown <david.brown@hesbynett.no> - 2017-11-23 09:39 +0100
                Re: [sot] file times / file metadata Jerry Stuckle <jstucklex@attglobal.net> - 2017-11-23 14:17 -0500
                Re: [sot] file times / file metadata cross@spitfire.i.gajendra.net (Dan Cross) - 2017-11-28 16:44 +0000
                Re: [sot] file times / file metadata Jerry Stuckle <jstucklex@attglobal.net> - 2017-11-28 14:23 -0500
                Re: [sot] file times / file metadata cross@spitfire.i.gajendra.net (Dan Cross) - 2017-11-28 19:35 +0000
                Re: [sot] file times / file metadata Jerry Stuckle <jstucklex@attglobal.net> - 2017-11-30 15:54 -0500
                Re: [sot] file times / file metadata cross@spitfire.i.gajendra.net (Dan Cross) - 2017-11-30 21:43 +0000
                Re: [sot] file times / file metadata Jerry Stuckle <jstucklex@attglobal.net> - 2017-12-04 11:42 -0500
                Re: [sot] file times / file metadata scott@slp53.sl.home (Scott Lurndal) - 2017-11-28 19:42 +0000
                Re: [sot] file times / file metadata cross@spitfire.i.gajendra.net (Dan Cross) - 2017-11-28 20:13 +0000
                Re: [sot] file times / file metadata Jerry Stuckle <jstucklex@attglobal.net> - 2017-11-30 15:57 -0500
                Re: [sot] file times / file metadata scott@slp53.sl.home (Scott Lurndal) - 2017-11-30 21:17 +0000
                Re: [sot] file times / file metadata jameskuyper@verizon.net - 2017-11-28 09:35 -0800
                Re: [sot] file times / file metadata Ian Collins <ian-news@hotmail.com> - 2017-11-29 08:24 +1300
                Re: [sot] file times / file metadata Ian Collins <ian-news@hotmail.com> - 2017-11-29 08:27 +1300
                Re: [sot] file times / file metadata Jerry Stuckle <jstucklex@attglobal.net> - 2017-11-28 14:29 -0500
                Re: [sot] file times / file metadata David Brown <david.brown@hesbynett.no> - 2017-11-29 09:51 +0100
                Re: [sot] file times / file metadata Jerry Stuckle <jstucklex@attglobal.net> - 2017-11-30 15:59 -0500
                Re: [sot] file times / file metadata David Brown <david.brown@hesbynett.no> - 2017-11-29 10:00 +0100
                Re: [sot] file times / file metadata "James R. Kuyper" <jameskuyper@verizon.net> - 2017-11-29 09:11 -0500
                Re: [sot] file times / file metadata David Brown <david.brown@hesbynett.no> - 2017-11-29 15:28 +0100
                Re: [sot] file times / file metadata "James R. Kuyper" <jameskuyper@verizon.net> - 2017-11-29 11:32 -0500
                Re: [sot] file times / file metadata James Kuyper <jameskuyper@verizon.net> - 2017-11-23 15:05 -0500
                Re: [sot] file times / file metadata David Brown <david.brown@hesbynett.no> - 2017-11-24 10:20 +0100
                Re: [sot] file times / file metadata Jerry Stuckle <jstucklex@attglobal.net> - 2017-11-24 09:05 -0500
                Re: [sot] file times / file metadata Robert Wessel <robertwessel2@yahoo.com> - 2017-11-24 22:50 -0600
                Re: [sot] file times / file metadata cross@spitfire.i.gajendra.net (Dan Cross) - 2017-11-28 16:59 +0000
                Re: [sot] file times / file metadata Ian Collins <ian-news@hotmail.com> - 2017-11-29 08:26 +1300
                Re: [sot] file times / file metadata David Brown <david.brown@hesbynett.no> - 2017-11-29 10:10 +0100
                Re: [sot] file times / file metadata cross@spitfire.i.gajendra.net (Dan Cross) - 2017-11-29 21:01 +0000
                Re: [sot] file times / file metadata David Brown <david.brown@hesbynett.no> - 2017-11-29 23:13 +0100
                Re: [sot] file times / file metadata cross@spitfire.i.gajendra.net (Dan Cross) - 2017-11-30 17:26 +0000
              Re: [sot] file times / file metadata fir <profesor.fir@gmail.com> - 2017-11-22 08:00 -0800
              Re: [sot] file times / file metadata "Pascal J. Bourguignon" <pjb@informatimago.com> - 2017-11-22 17:11 +0100
            Re: [sot] file times / file metadata "Pascal J. Bourguignon" <pjb@informatimago.com> - 2017-11-22 16:51 +0100
              Re: [sot] file times / file metadata scott@slp53.sl.home (Scott Lurndal) - 2017-11-22 16:36 +0000

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