From: Corinna Vinschen <corinna-cygwin@cygwin.com>
To: cygwin@cygwin.com
Subject: Re: Cygwin api to punch a hole into a file?
Date: Tue, 5 Dec 2023 16:15:14 +0100 [thread overview]
Message-ID: <ZW8-gioc3j9qTYu_@calimero.vinschen.de> (raw)
In-Reply-To: <06bd1d13-7d60-4e45-b597-70816a2ad559@towo.net>
On Dec 5 15:47, Thomas Wolff via Cygwin wrote:
>
> Am 05/12/2023 um 15:40 schrieb Thomas Wolff via Cygwin:
> > Am 05/12/2023 um 14:53 schrieb Corinna Vinschen via Cygwin:
> > > On Dec 5 07:36, Thomas Wolff via Cygwin wrote:
> > > >
> > > > Am 01.12.2023 um 12:02 schrieb Corinna Vinschen via Cygwin:
> > > > > On Dec 1 11:22, Cedric Blancher via Cygwin wrote:
> > > > > > Not all filesystems have a 128k block/stripe size, and certainly most
> > > > > > filesystems have smaller minimum hole sizes than 128k (e.g. 512bytes
> > > > > > is common, ref pathconf _PC_MIN_HOLE_SIZE).
> > > > > There's no _PC_MIN_HOLE_SIZE in Linux or POSIX. In Windows, a sparse
> > > > > file uses chunks of 64K. You can see this even with a file of just
> > > > > a single block. Try this:
> > > > >
> > > > > $ touch x
> > > > > $ chattr +S x
> > > > >
> > > > > $ echo 1234567890123456789012345678901234567890123456789012345678901234567890123456789
> > > > > >> x
> > > > > $ ls -ls x
> > > > > 1 -rw-r--r-- 1 corinna vinschen 80 Dec 1 11:56 x
> > > > >
> > > > > [repeat echo and ls -ls until...]
> > > > >
> > > > > $ echo 1234567890123456789012345678901234567890123456789012345678901234567890123456789
> > > > > >> x
> > > > > $ ls -ls x
> > > > > 1 -rw-r--r-- 1 corinna vinschen 720 Dec 1 11:56 x
> > > > > $ echo 1234567890123456789012345678901234567890123456789012345678901234567890123456789
> > > > > >> x
> > > > > $ ls -ls x
> > > > > 64 -rw-r--r-- 1 corinna vinschen 800 Dec 1 11:56 x2
> > > > > ^^
> > > > > This
> > > > For me, it goes up from 1 to 4, then in steps of 4KB.
> > > Is that a local NTFS, did you actually call
> > >
> > > chattr +S x
> > >
> > > after touching the file, and did you check with
> > >
> > > lsattr x
> > >
> > > that x is actually sparse?
> > Ups, sorry, I was just throwing my 2p into something. Yes, on a local
> > NTFS; setting chattr +s does not change it but lsattr says:
> > ---a-------- .ls-s
> >
> > So why does chattr not seem to work?
> Sorry again, I failed to test properly (I had copied your `chattr +S x`
> which is not the filename I tested... blush).
> With chattr +S, I reproduce your observation.
No worries. Thanks for testing and confirming!
Corinna
next prev parent reply other threads:[~2023-12-05 15:15 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-11-23 22:36 Cedric Blancher
2023-11-24 11:01 ` Corinna Vinschen
2023-11-28 10:29 ` Corinna Vinschen
2023-12-01 10:22 ` Cedric Blancher
2023-12-01 11:02 ` Corinna Vinschen
2023-12-04 16:07 ` Andrey Repin
2023-12-05 6:36 ` Thomas Wolff
2023-12-05 13:53 ` Corinna Vinschen
2023-12-05 14:40 ` Thomas Wolff
2023-12-05 14:47 ` Thomas Wolff
2023-12-05 15:15 ` Corinna Vinschen [this message]
2023-12-01 10:44 ` _PC_MIN_HOLE_SIZE pathconf() " Cedric Blancher
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