[Gluster-devel] Dht readdir filtering out names

[Raghavendra Gowdappa]

----- Original Message -----
> From: "Pranith Kumar Karampuri" <pkarampu at redhat.com>
> To: "Raghavendra Gowdappa" <rgowdapp at redhat.com>
> Cc: "Shyam Ranganathan" <srangana at redhat.com>, "Nithya Balachandran" <nbalacha at redhat.com>, "Gluster Devel"
> <gluster-devel at gluster.org>
> Sent: Friday, September 30, 2016 9:15:04 AM
> Subject: Re: Dht readdir filtering out names
> 
> On Fri, Sep 30, 2016 at 9:13 AM, Raghavendra Gowdappa <rgowdapp at redhat.com>
> wrote:
> 
> > dht_readdirp_cbk has different behaviour for directories and files.
> >
> > 1. If file, pick the dentry (passed from subvols as part of readdirp
> > response) if the it corresponds to data file.
> > 2. If directory pick the dentry if readdirp response is from hashed-subvol.
> >
> > In all other cases, the dentry is skipped and not passed to higher
> > layers/application. To elaborate, the dentries which are ignored are:
> > 1. dentries corresponding to linkto files.
> > 2. dentries from non-hashed subvols corresponding to directories.
> >
> > Since the behaviour is different for different filesystem objects, dht
> > needs ia_type to choose its behaviour.
> >
> > ----- Original Message -----
> > > From: "Pranith Kumar Karampuri" <pkarampu at redhat.com>
> > > To: "Shyam Ranganathan" <srangana at redhat.com>, "Raghavendra Gowdappa" <
> > rgowdapp at redhat.com>, "Nithya Balachandran"
> > > <nbalacha at redhat.com>
> > > Cc: "Gluster Devel" <gluster-devel at gluster.org>
> > > Sent: Friday, September 30, 2016 8:39:28 AM
> > > Subject: Dht readdir filtering out names
> > >
> > > hi,
> > >        In dht_readdirp_cbk() there is a check about skipping files
> > without
> > > ia_type. Could you help me understand why this check is added? There are
> > > times when users have to delete gfid of the entries and trigger something
> > > like 'find . | xargs stat' to heal the gfids. This case would fail if we
> > > skip entries without gfid, if the lower xlators don't send stat
> > information
> > > for them.
> >
> > Probably we can make readdirp_cbk not rely on ia_type and pass _all_
> > dentries received by subvols to application without filtering. However we
> > should make this behaviour optional and use this only for recovery setups.
> > If we don't rely on ia_type (during non error scenarios), applications end
> > up seeing duplicate dentries in readdir listing.
> >
> 
> That means dht_readdir() gives duplicate entries? As per the code it seems
> like it...

No. It follows the filtering logic of "pick dentry only from hashed subvol". This logic doesn't need ia_type. Now, that you brought the topic of dht_readdir, I've another solution for your use case (Basically don't use readdirp :) ):

1. mount glusterfs with "--use-readdirp=no" option.
2. disable md-cache/stat-prefetch as it converts all readdir calls into readdirp calls

Use this only for recovery setups :).

> 
> 
> >
> > >
> > > --
> > > Pranith
> > >
> >
> > regards,
> > Raghavendra
> >
> 
> 
> 
> --
> Pranith
>