[Bugs] [Bug 1394298] Add hole punch support

[bugzilla at redhat.com]

https://bugzilla.redhat.com/show_bug.cgi?id=1394298

Ravishankar N <ravishankar at redhat.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |areddy at commvault.com,
                   |                            |ravishankar at redhat.com
           Assignee|bugs at gluster.org            |ravishankar at redhat.com
              Flags|                            |needinfo?(areddy at commvault.
                   |                            |com)



--- Comment #1 from Ravishankar N <ravishankar at redhat.com> ---
Hi Ram, Need some clarification here. What I meant to say in the mailing-list
thread was fallocate with keep-size flag (and therefore the hole-punch flag
also) will report incorrect disk usage for the file:


On a normal XFS file system:
==============================
0:root at vm4 ~$ #create a file.
0:root at vm4 ~$ echo > file
0:root at vm4 ~$ #fallocate 1G with keep size flag.
0:root at vm4 ~$ fallocate -o0 -l1G -n file
0:root at vm4 ~$ #check file size and disk space usage.
0:root at vm4 ~$ ll -h file
-rw-r--r--. 1 root root 1 Nov 11 22:09 file
0:root at vm4 ~$ du -h file
1.0G    file
0:root at vm4 ~$
0:root at vm4 ~$ #punch 512MB hole and check usage again
0:root at vm4 ~$ fallocate -o0 -l512M -p file
0:root at vm4 ~$ ll -h file
-rw-r--r--. 1 root root 1 Nov 11 22:10 file
0:root at vm4 ~$ du -h file
512M    file
0:root at vm4 ~$


On a normal plain distribute 1 brick volume using fuse mount:
===============================================================
0:root at vm4 fuse_mnt$ echo >file
0:root at vm4 fuse_mnt$ fallocate -o0 -l1G -n file
0:root at vm4 fuse_mnt$ ll -h file
-rw-r--r--. 1 root root 1 Nov 11 22:13 file
0:root at vm4 fuse_mnt$ du -h file
512     file -->This is wrong.
0:root at vm4 fuse_mnt$
0:root at vm4 fuse_mnt$ #run the command on the backend brick and observe correct
disk usage is reported.
0:root at vm4 fuse_mnt$
0:root at vm4 fuse_mnt$ ll -h /bricks/brick1/file
-rw-r--r--. 2 root root 1 Nov 11 22:13 /bricks/brick1/file
0:root at vm4 fuse_mnt$ du -h /bricks/brick1/file
1.0G    /bricks/brick1/file
0:root at vm4 fuse_mnt$
0:root at vm4 fuse_mnt$
0:root at vm4 fuse_mnt$ #punch hole
0:root at vm4 fuse_mnt$ fallocate -o0 -l^C
130:root at vm4 fuse_mnt$ fallocate -o0 -l512M -p file
0:root at vm4 fuse_mnt$ ll -h file
-rw-r--r--. 1 root root 1 Nov 11 22:14 file
0:root at vm4 fuse_mnt$ du -h file
512     file
0:root at vm4 fuse_mnt$
0:root at vm4 fuse_mnt$ ll -h /bricks/brick1/file
-rw-r--r--. 2 root root 1 Nov 11 22:14 /bricks/brick1/file
0:root at vm4 fuse_mnt$ du -h /bricks/brick1/file
512M    /bricks/brick1/file
0:root at vm4 fuse_mnt$
========================================

But you seem to be saying punch hole *fails* on the file. Not sure if we are on
the same page here. Does this happen only on disperse volumes? Can you explain
the steps in detail?

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