From: Thomas Wolff <towo@towo.net>
To: cygwin@cygwin.com
Subject: Re: Cygwin api to punch a hole into a file?
Date: Tue, 5 Dec 2023 15:47:58 +0100 [thread overview]
Message-ID: <06bd1d13-7d60-4e45-b597-70816a2ad559@towo.net> (raw)
In-Reply-To: <12e1d9d9-bc56-456e-a1ab-c760987f3ac2@towo.net>
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.
> Thomas
>
>> Corinna
>>
>
>
next prev parent reply other threads:[~2023-12-05 14:48 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 [this message]
2023-12-05 15:15 ` Corinna Vinschen
2023-12-01 10:44 ` _PC_MIN_HOLE_SIZE pathconf() " Cedric Blancher
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