[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 10:04:29 AM
> Subject: Re: Dht readdir filtering out names
> 
> What if the lower xlators want to set the entry->inode to NULL and clear
> the entry->d_stat to force a lookup on the name? i.e.
> gfid-split-brain/ia_type mismatches.

Didn't get you. If you are using readdirp, as you pointed out dht_readdirp won't work properly if entry->d_stat is zeroed out. So, the entry won't be listed and if it is not listed, we cannot force a lookup on that.

> 
> On Fri, Sep 30, 2016 at 10:00 AM, Raghavendra Gowdappa <rgowdapp at redhat.com>
> wrote:
> 
> >
> >
> > ----- Original Message -----
> > > From: "Raghavendra Gowdappa" <rgowdapp at redhat.com>
> > > To: "Pranith Kumar Karampuri" <pkarampu 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 9:58:34 AM
> > > Subject: Re: Dht readdir filtering out names
> > >
> > >
> > >
> > > ----- 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 9:53:44 AM
> > > > Subject: Re: Dht readdir filtering out names
> > > >
> > > > On Fri, Sep 30, 2016 at 9:50 AM, Raghavendra Gowdappa <
> > rgowdapp at redhat.com>
> > > > wrote:
> > > >
> > > > >
> > > > >
> > > > > ----- 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
> > > > >
> > > >
> > > > Probably the ones in dht as well? i.e. use-readdirp option.
> > >
> > > No. dht doesn't convert a readdir into readdirp. The option you are
> > referring
> > > to might be "readdir-optimize" which is something different.
> >
> > Sorry. I was wrong. There is an option in dht too, to force using
> > readdirp. As you said, we should disable that too.
> >
> > >
> > > >
> > > >
> > > > >
> > > > > Use this only for recovery setups :).
> > > > >
> > > > > >
> > > > > >
> > > > > > >
> > > > > > > >
> > > > > > > > --
> > > > > > > > Pranith
> > > > > > > >
> > > > > > >
> > > > > > > regards,
> > > > > > > Raghavendra
> > > > > > >
> > > > > >
> > > > > >
> > > > > >
> > > > > > --
> > > > > > Pranith
> > > > > >
> > > > >
> > > >
> > > >
> > > >
> > > > --
> > > > Pranith
> > > >
> > >
> >
> 
> 
> 
> --
> Pranith
>