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838 :: Bug in memfiles?

• andrea (orginal) [2015-02-06T11:44:42+01:00] view original

  Hi, I am trying to map a file into memory, starting with an offset, and I think I have stumbled into a bug. Maybe I am just misunderstanding how to use memfiles.

  Anyway, the following works fine

  import memfiles, os
  
  var c = memfiles.open(paramStr(1), mappedSize = 2, offset = 0)
  echo c.size
  Run

  but when I add an offset, it fails

  import memfiles, os
  
  var c = memfiles.open(paramStr(1), mappedSize = 2, offset = 1)
  echo c.size
  Run

  Error: unhandled exception: Invalid argument [OSError].

  If it helps, I am on Ubuntu 14.04. Any ideas why this should fail?

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• def (orginal) [2015-02-06T12:26:55+01:00] view original

  Reading the manpage on mmap reveals: http://linux.die.net/man/2/mmap

  The contents of a file mapping (as opposed to an anonymous mapping; see MAP_ANONYMOUS below), are initialized using length bytes starting at offset offset in the file (or other object) referred to by the file descriptor fd. offset must be a multiple of the page size as returned by sysconf(_SC_PAGE_SIZE).

  This should of course be documented in the memfiles module.

  import posix
  echo sysconf(SC_PAGE_SIZE)
  Run

  Prints 4096 on my system.

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• andrea (orginal) [2015-02-06T12:37:40+01:00] view original

  Thank you, I see

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