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Date: | Tue, 5 Dec 2023 16:15:14 +0100 |
To: | cygwin AT cygwin DOT com |
Subject: | Re: Cygwin api to punch a hole into a file? |
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From: | Corinna Vinschen via Cygwin <cygwin AT cygwin DOT com> |
Reply-To: | cygwin AT cygwin DOT com |
Cc: | Corinna Vinschen <corinna-cygwin AT cygwin DOT com> |
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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 -- Problem reports: https://cygwin.com/problems.html FAQ: https://cygwin.com/faq/ Documentation: https://cygwin.com/docs.html Unsubscribe info: https://cygwin.com/ml/#unsubscribe-simple
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