Re: Why does (stat() ?) open files ?

[Corinna Vinschen <corinna-cygwin at cygwin dot com>]

On Apr  9 12:28, Ben RUBSON wrote:
> Hi,
> 
> This follows the "Why does readdir() open files ?" discussion we had a few
> days ago.
> Thank you Corinna for your answers and suport there !
> 
> So, context is Cygwin, especially rsync, working over a Fuse FS.
> This Fuse FS is assumed to be mounted on `/cygdrive/x` below.
> 
> I finally found that readdir() does not open every file.
> `ls /cygdrive/x` does not fire any open() call. Perfect.
> 
> However, `ls -l /cygdrive/x` does, every file is opened, with read access.
> As `rsync -an /cygdrive/x /tmp/`, which is a dry-run just grabbing files'
> attributes.
> 
> I then went through Cygwin code and found that NtCreateFile/NtOpenFile calls
> from symlink_info::check() in path.cc may be the culprits.
> To demonstrate this I added write access to these calls, and found that
> every file was then opened with write access.
> 
> Later in this function we have a failback to NtQueryDirectoryFile call.
> I assume (assume only, I may be wrong) this one does not open the requested
> file.

It's nice that you're testing all this, but you should ask *why* Cygwin
does it in the first place.  The reason is that the information one can
gather without opening the file on Windows is insufficient to fill in
all of the stat struct.  The directory info returned by
NtQueryDirectoryFile just isn't, thus it's only a fallback.


Corinna

-- 
Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Maintainer                 cygwin AT cygwin DOT com
Red Hat

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