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Date: Sat, 27 Jun 2026 17:53:34 +0200
Message-ID: <CALXu0UfRUnLF_Vqk2hc4Lm2et=GcTMvxqK+Zd2tmhMrcdTF3eg@mail.gmail.com>
Subject: Re: Cygwin sparse file support: Please support fcntl(..., F_FREESP,
 ...)
To: cygwin@cygwin.com
From: Cedric Blancher via Cygwin <cygwin@cygwin.com>
Reply-To: Cedric Blancher <cedric.blancher@gmail.com>
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The code works for me, but we need this in Cygwin, and not an addon.

Ced

On Wed, 24 Jun 2026 at 14:27, Roland Mainz via Cygwin <cygwin@cygwin.com> wrote:
>
> On Sat, Feb 15, 2025 at 4:14 PM Cedric Blancher via Cygwin
> <cygwin@cygwin.com> wrote:
> > Could Cygwin 3.6 please support fcntl(...,F_FREESP,...) and
> > cntl(...,F_FREESP64,...), as specified in
> > https://docs.oracle.com/cd/E19253-01/816-5167/fcntl-2/index.html
> >
> > Lots of older software from Solaris, SUPER/UX, CrayOS use F_FREESP for
> > punching a hole into a file, and IMO it'll be nice if this works for
> > Cygwin out of the box.
>
> 1. Ced: Could you please check whether the prototype code works for
> you ? If "yes" then I'll make a patch for cygwin.dll based on this...
> 2. Takashi: What do you think ? The API comes from Solaris, and is
> implememted by at least FreeBSD, Unicos, SUPER/UX, etc. and is usually
> used by database and HPC software.
>
> Prototype patch:
> ---- snip ----
> #ifndef F_FREESP
> #define F_FREESP   15
> #endif
>
> #ifndef F_ALLOCSP
> #define F_ALLOCSP  16
> #endif
>
> /* FIXME: This should use a |struct flock| like Solaris/FreeBSD |fnctl()| */
> int fcntl_sparse_space_management_emulate(int fd, int cmd, off_t
> offset, off_t len)
> {
>     off_t file_size;
>     off_t end;
>
>     file_size = lseek(fd, 0, SEEK_END);
>     if (file_size == (off_t)-1)
>         return -1;
>
>     if (len == 0)
>         end = file_size;
>     else
>         end = offset + len;
>
>     switch (cmd) {
>
>     case F_FREESP:
>         if (offset >= file_size)
>             return 0;
>
>         if (end >= file_size) {
>             return ftruncate(fd, offset);
>         } else {
>             if (fallocate(fd,
>                           FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE,
>                           offset,
>                           end - offset) == -1) {
>                 return -1;
>             }
>         }
>         return 0;
>
>     case F_ALLOCSP:
>         if (len == 0) {
>             return 0;
>         }
>
>         if (fallocate(fd, 0, offset, len) == -1) {
>             return -1;
>         }
>
>         return 0;
>
>     default:
>         errno = EINVAL;
>         return -1;
>     }
> }
> ---- snip ----
>
> ----
>
> Bye,
> Roland
> --
>   __ .  . __
>  (o.\ \/ /.o) roland.mainz@nrubsig.org
>   \__\/\/__/  MPEG specialist, C&&JAVA&&Sun&&Unix programmer
>   /O /==\ O\  TEL +49 641 3992797
>  (;O/ \/ \O;)
>
> --
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-- 
Cedric Blancher <cedric.blancher@gmail.com>
[https://plus.google.com/u/0/+CedricBlancher/]
Institute Pasteur

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