[Gluster-devel] Get GFID for a file through libgfapi

[Ankireddypalle Reddy]

Neils,
             Thanks a lot. Will use this for extracting GFID.

Ram

-----Original Message-----
From: Niels de Vos [mailto:ndevos at redhat.com] 
Sent: Tuesday, January 10, 2017 4:26 AM
To: Ankireddypalle Reddy
Cc: Gluster Devel (gluster-devel at gluster.org); integration at gluster.org
Subject: Re: [Gluster-devel] Get GFID for a file through libgfapi

On Mon, Jan 09, 2017 at 08:58:07PM +0000, Ankireddypalle Reddy wrote:
> Neils,
>             Thanks for pointing to the sample code. The use case is to use  GFID as a unique key for maintaining indexing information about a file when it is being backed up from GlusterFS storage.  Extending GFAPI to extract GFID for a file would be great.
>              As  per the example If I need to find GFID for a path p1/p2/p3/p4 on a glusterfs volume then should I do a look up for every level?
>              LOOKUP (/)->LOOKUP(p1)-> LOOKUP(p2)-> LOOKUP(p3)-> 
> LOOKUP(p4)

No, that is not required. You can use glfs_h_lookupat() with the full path. Note that glfs_h_extract_handle() just does a memcpy() of the GFID into the given (unsigned char*), the format is of 'uuid_t'.

Attached is the modified test that shows the UUID without the need for a lookup of each component of the directory (a LOOKUP will be done by gfapi if needed).

  $ make CFLAGS="-lgfapi -luuid" resolve
  cc -lgfapi -luuid    resolve.c   -o resolve
  $ ./resolve storage.example.com media resolve.log
  Starting libgfapi_fini
  glfs_set_volfile_server : returned 0
  glfs_set_logging : returned 0
  glfs_init : returned 0
  glfs_set_volfile_server : returned 0
  glfs_set_logging : returned 0
  glfs_init : returned 0
  glfs_h_extract_handle : returned 0
  UUID of /installation/CentOS-7-x86_64-Everything-1503-01.iso: b1b20352-c71c-4579-b678-a7a38b0e9a84
  glfs_fini : returned 0
  End of libgfapi_fini
  
  $ getfattr -n glusterfs.gfid -ehex /lan/storage.example.com/media/installation/CentOS-7-x86_64-Everything-1503-01.iso
  getfattr: Removing leading '/' from absolute path names
  # file: lan/storage.example.com/media/installation/CentOS-7-x86_64-Everything-1503-01.iso
  glusterfs.gfid=0xb1b20352c71c4579b678a7a38b0e9a84

HTH,
Niels


> 
> Thanks and Regards,
> Ram
> 
> 
> -----Original Message-----
> From: Niels de Vos [mailto:ndevos at redhat.com]
> Sent: Monday, January 09, 2017 3:39 PM
> To: Ankireddypalle Reddy
> Cc: Gluster Devel (gluster-devel at gluster.org); integration at gluster.org
> Subject: Re: [Gluster-devel] Get GFID for a file through libgfapi
> 
> On Mon, Jan 09, 2017 at 05:53:03PM +0000, Ankireddypalle Reddy wrote:
> > Hi,
> >         I am trying to extract the GFID for a file through libgfapi interface. When I try to extract the value of extended attribute glusterfs.gfid through libgfapi I get the errorno: 95.  This works for FUSE though. Is there a way to extract the GFID for a file through libgfapi.
> 
> It seems that this is a case where FUSE handles the xatts special. The 
> glusterfs.gfid and glusterfs.gfid.string (VIRTUAL_GFID_XATTR_KEY and
> VIRTUAL_GFID_XATTR_KEY_STR) are specifically handled in xlators/mount/fuse/src/fuse-bridge.c.
> 
> There is a way to get the GFID, but it probably is rather a cumbersome 
> workaround for you. The handle-API is used heavily by NFS-Ganesha 
> (because NFS uses filehandles more than filenames), and extracts the 
> GFID from the 'struct glfs_object' with glfs_h_extract_handle(). A 
> basic example of how to obtain and extract the handle is in 
> https://github.com/gluster/glusterfs/blob/master/tests/basic/gfapi/bug
> 1291259.c
> 
> Could you explain the need for knowing the GFID in the application? We can extend gfapi with fetching the GFID if that would help you.
> 
> Niels
> 
> 
> PS: we have a new integration at gluster.org where external projects can ask gfapi related questions. The gluster-devel list tends to be a little heavy on traffic for non-Gluster developers.
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