Re: SEEK_HOLE Support in Cygwin?

[Corinna Vinschen <corinna-cygwin@cygwin.com>]

On Aug 25 13:23, Corinna Vinschen wrote:
> On Aug 25 13:09, Roland Mainz wrote:
> > On Fri, Aug 25, 2023 at 11:05 AM Corinna Vinschen
> > <corinna-cygwin@cygwin.com> wrote:
> > >
> > > On Aug 24 14:03, Roland Mainz wrote:
> > > > Question for Corinna:
> > >
> > > Everybody involved in the project could answer this question, but...
> > >
> > > > Does Cygwin support allocation/deallocation of filesystem blocks via
> > > > Linux's |fallocate()|-API ?
> > >
> > > ...just try this:
> > >
> > > $ cat > a.c <<EOF
> > > extern void fallocate();
> > > extern void posix_fallocate();
> > >
> > > int main()
> > > {
> > >   fallocate();
> > >   posix_fallocate();
> > > }
> > > EOF
> > > $ gcc -o a a.c
> > 
> > Thanks...
> > ... I saw that the functions are there,
> 
> So you didn't actually run the test?
> 
> > but my question was more like
> > "supports"=="calls native Windows API".
> > 
> > |fallocate()| support seems to be in
> > ./newlib-cygwin/winsup/cygwin/fhandler/disk_file.cc, and supports the
> > allocation of blocks - but I couldn't find support for
> > |FALLOC_FL_PUNCH_HOLE|, e.g. deallocation of blocks (to "punch" a hole
> > into the file).
> > Is this an oversight, or does Window's native API not support that ?
> 
> If you found fallocate() in fhandler/disk_file.cc, I need new glasses.

No, we don't support fallocate, we only support posix_fallocate.
The flags to fallocate can be supported like this:

  0				== posix_fallocate
  FALLOC_FL_KEEP_SIZE		posix_fallocate with forcing sparse
  FALLOC_FL_UNSHARE_RANGE	no-op
  FALLOC_FL_PUNCH_HOLE		use Windows ioctl FSCTL_SET_ZERO_DATA

https://cygwin.com/acronyms/#SHTDI


Corinna