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Subject: Re: Question about slow access to file information
To: cygwin <cygwin AT cygwin DOT com>
References: <797a8935-e38b-0c0f-87d8-b8df1e9fd76f AT cs DOT umass DOT edu>
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Date: Sat, 14 Jan 2023 17:38:42 +0100
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From: Christian Franke via Cygwin <cygwin AT cygwin DOT com>
Reply-To: Christian Franke <Christian DOT Franke AT t-online DOT de>
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Eliot Moss via Cygwin wrote:
> I have a separate drive mounted this way:
>
> d:/ /cygdrive/d ntfs binary,posix=0,user,noacl,auto 0 0
>
> One thing I use it for is to store backup files.  These tend to be 2 Gb
> chunks, and there can be hundreds of them in the backup directory.  
> (The drive
> is 5Tb.)  The Windows Disk Management tool describes it as NTFS, Basic 
> Data
> Partition.
>
> Doing ls (for example) takes a very perceptible numbers of seconds 
> (though
> whatever takes a long time seems to be cached, at least for a while, 
> since a
> second ls soon after is fast).

The problem is the 'noacl' mount option and the fact that POSIX only 
offers the *stat*() functions to retrieve file information. These 
functions always need to provide the full file information, even if only 
a small subset is needed.

To determine the 'x'-permission bits in the 'stat.st_mode' field on a 
'noacl'-mount, Cygwin reads the first bytes of most files (all except 
*.exe, *.lnk, *.com). The 'x' bits are set if the file starts with "#!" 
(script), ":\n" (?) or "MZ" (Windows executable).

On 'noacl' mounts, this behavior could be suppressed by 'exec' or 
'noexec' mount options.

-- 
Regards,
Christian


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