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bug#29259: tail does not seek to the end of block device

From: Pádraig Brady
Subject: bug#29259: tail does not seek to the end of block device
Date: Sun, 12 Nov 2017 21:50:29 -0800
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.8.0

On 11/11/17 12:08, David Durham wrote:
> sudo tail -c 1024 /dev/sda2 | hd  the entire /dev/sda2 device rather than
> seeking to the end. This takes a very long time with large disks. Deltik
> gives a nice explanation here -
> https://superuser.com/questions/1267402/how-do-i-tail-a-block-device-in-linux
> - of how ioctl can be used to obtain the size of a block device instead of
> fstat.
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Yes maybe. The answer at the link shows how to do it efficiently with
the existing `dd` and `blockdev --getsize64` tools.
I also mentioned there the iflag=skip_bytes option which allows
one to efficiently skip portions of a disk independently from the I/O size.

Given dd is a more natural tool for dealing with device I/O,
and that processing the end of a device is an unusual use case,
I'm on the fence as to whether `tail` should handle this case specially.


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