Why does readdir() open files ?

Corinna Vinschen corinna-cygwin@cygwin.com
Wed Mar 28 17:03:00 GMT 2018


On Mar 28 18:35, Ben RUBSON wrote:
> On 28 Mar 2018, Ben RUBSON wrote:
> 
> > Hi,
> > 
> > I'm porting a FUSE FS to Cygwin, and I focus especially on readdir()
> > performance.
> > 
> > What I see is that when readdir() occurs, each file of the directory is
> > as expected (at least I think) stated (getattr), but also opened (open).
> > The first block of the file was even red, until I set the notexec mount
> > option.
> > 
> > My question is, why is every file opened ?
> > This is quite a performance killer, particularly for a FUSE FS.
> > 
> > I thought this was to calculate the inode number, I then set the ihash
> > mount option, but it did not help.
> 
> I may be totally wrong, but perhaps the culprit is the following code path ?
> https://github.com/mirror/newlib-cygwin/blob/master/winsup/cygwin/fhandler_disk_file.cc#L2262
> Perhaps we simply don't need to open the file if (!hasgood_inode ()) ?
> 
> That would be a nice performance improvement !

You should make sure that the hasgood_inode() check works for your FUSE
FS.  Check at the end of fs_info::update():

  has_acls (flags () & FS_PERSISTENT_ACLS);
  /* Netapp inode numbers are fly-by-night. */
  hasgood_inode ((has_acls () && !is_netapp ()) || is_nfs ());

So your filesystem should return the FS_PERSISTENT_ACLS flags in a call
to NtQueryVolumeInformationFile(..., FileFsAttributeInformation)


Corinna

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