Fwd: Re: cp command - problem with sparse

Christopher Faylor cgf-no-personal-reply-please@cygwin.com
Tue Feb 1 14:59:00 GMT 2005

On Tue, Feb 01, 2005 at 06:48:56AM -0700, Eric Blake wrote:
>This question came up on the coreutils list:
>Does cygwin provide any support for sparse files on NTFS volumes that
>support it?  lseek() could be patched to use FSCTL_SET_ZERO_DATA when a
>seek jumps past the end of a file open for writing, but there is still the
>issue of when that file is given the FSCTL_SET_SPARSE attribute.


  % fgrep FSCTL_SET_SPARSE *.cc
  fhandler.cc:          BOOL r = DeviceIoControl (h, FSCTL_SET_SPARSE, NULL, 0, NULL,
  fhandler.cc:          syscall_printf ("%d = DeviceIoControl(%p, FSCTL_SET_SPARSE, "

There are limitations on when a file is considered sparse, however.  The archives
probably have more details.


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