Show transfer status with pv

[quantumphaze]

Have an option flag that pipes the transfer through the pv utility. pv monitors data going through a pipe, alowing things like counting the bytes transfered.

Should be something like

btrfs send $SRC | pv | btrfs receive $DEST

Note that pv has no way of knowing the total amount of data that needs to be tranfered since send/receive doesn't know, it just counts the bytes. (If I am mistakened and there is a way to determine the side of a snapshot then there is a flag to add that.)

[digint]

Thanks for the input, should be pretty easy to implement, and is definitvely useful when starting btrbk interactively.
The output looks promising:

# btrfs send /mnt/btr_pool/_btrbk_snap/rootfs.20150815 | pv > /dev/null
At subvol /mnt/btr_pool/_btrbk_snap/rootfs.20150815
317MiB 0:00:03 [577.2MiB/s] [   <=>                                                      ]

I guess I will implement a "-V" option switch for this.

[quantumphaze]

I would suguest a --progress flag similar to the equivalent flag in rsync because -V is often used as shorthand for --version

[digint]

Yes you're right. The problem is that btrbk does not support long ("--") arguments. On the other side, as btrbk grows I'll have to support this anyways some day.

[digint]

implemented "--progress" option in: d8e8df0

@quantumphaze feel free to reopen this issue if you have more suggestions!