From: Corinna Vinschen <corinna-cygwin@cygwin.com>
To: cygwin-developers@cygwin.com
Subject: Re: SEEK_HOLE Support in Cygwin?
Date: Mon, 21 Aug 2023 10:32:58 +0200 [thread overview]
Message-ID: <ZOMhOtPAcqttYcWA@calimero.vinschen.de> (raw)
In-Reply-To: <CALXu0Uc7CYc4LQZCw_3zumgxHbmE+RTcy9P26FdvSKvCfc-exQ@mail.gmail.com>
On Aug 21 06:33, Cedric Blancher wrote:
> On Thu, 10 Aug 2023 at 10:28, Corinna Vinschen
> <corinna-cygwin@cygwin.com> wrote:
> > On Aug 10 04:43, Cedric Blancher wrote:
> > > So this supports multiple holes in one file, right?
> >
> > Curious question. Cygwin supports sparse files for ages. Only the
> > lseek options SEEK_HOLE and SEEK_DATA are new.
>
> Is SEEK_HOLE support enabled for MSFT NFSv3 client?
NFSv3 doesn't return the FILE_SUPPORTS_SPARSE_FILES capability and
doesn't support Windows sparse file functions. Sparsification is
(correctly) the responsibility of the remote file system.
> > But, yes, it supports what Windows supports. But note that Cygwin
> > *only* switches files to sparse, if you seek by more than 128K beyond
> > current EOF and then wrote something, or if you call truncate/ftruncate,
> > raising the filesize by more than 128K.
>
> Where does the value of 128K come from? Is this a Windows limit,
> kernel tunable, or something from Cygwin?
Something from Cygwin.
> > In contrast to Linux, one has to sparsify a file explicitely on WIndows,
> > and that's Cygwin's strategy.
>
> Maybe add a O_SPARSEFILE to open/openat()?
We won't add any non-standard or non-Linux open flags. You can use
the chattr/lsattr tools.
> > > Why is "sparse" not the default mount option?
> >
> > It was, at one point long ago. People complained that sparse file
> > access is slower than standard file access, so the "sparse" mount option
> > was added.
>
> Do you have any refs in the mailing list?
Not without searching myself.
Corinna
next prev parent reply other threads:[~2023-08-21 8:33 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-08-06 17:14 Cedric Blancher
2023-08-07 8:33 ` Corinna Vinschen
2023-08-09 15:30 ` Corinna Vinschen
2023-08-10 2:43 ` Cedric Blancher
2023-08-10 8:28 ` Corinna Vinschen
2023-08-21 4:33 ` Cedric Blancher
2023-08-21 8:32 ` Corinna Vinschen [this message]
2023-08-24 12:03 ` Roland Mainz
2023-08-25 9:05 ` Corinna Vinschen
2023-08-25 11:09 ` Roland Mainz
2023-08-25 11:23 ` Corinna Vinschen
2023-08-25 11:43 ` Corinna Vinschen
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