selftests/zram: Adapt the situation that /dev/zram0 is being used

If zram-generator package is installed and works, then we can not remove
zram module because zram swap is being used. This case needs a clean zram
environment, change this test by using hot_add/hot_remove interface. So
even zram device is being used, we still can add zram device and remove
them in cleanup.

The two interface was introduced since kernel commit 6566d1a32bf7("zram:
add dynamic device add/remove functionality") in v4.2-rc1. If kernel
supports these two interface, we use hot_add/hot_remove to slove this
problem, if not, just check whether zram is being used or built in, then
skip it on old kernel.

Signed-off-by: Yang Xu <xuyang2018.jy@fujitsu.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 25

Based on 1 normalized pattern(s):

this program is free software you can redistribute it and or modify
it under the terms of the gnu general public license as published by
the free software foundation either version 2 of the license or at
your option any later version this program is distributed in the
hope that it would be useful but without any warranty without even
the implied warranty of merchantability or fitness for a particular
purpose see the gnu general public license for more details

extracted by the scancode license scanner the SPDX license identifier

GPL-2.0-or-later

has been chosen to replace the boilerplate/reference in 6 file(s).

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Steve Winslow <swinslow@gmail.com>
Reviewed-by: Kate Stewart <kstewart@linuxfoundation.org>
Reviewed-by: Jilayne Lovejoy <opensource@jilayne.com>
Reviewed-by: Allison Randal <allison@lohutok.net>
Cc: linux-spdx@vger.kernel.org
Link: https://lkml.kernel.org/r/20190519154043.007767574@linutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

selftests/zram: must be run as root

Adding new functionality check_prereqs() to check test must be run as root

Signed-off-by: Naresh Kamboju <naresh.kamboju@linaro.org>
Signed-off-by: Shuah Khan <shuahkh@osg.samsung.com>

selftests/zram: Adding zram tests

zram: Compressed RAM based block devices
----------------------------------------
The zram module creates RAM based block devices named /dev/zram<id>
(<id> = 0, 1, ...). Pages written to these disks are compressed and stored
in memory itself. These disks allow very fast I/O and compression provides
good amounts of memory savings. Some of the usecases include /tmp storage,
use as swap disks, various caches under /var and maybe many more :)

Statistics for individual zram devices are exported through sysfs nodes at
/sys/block/zram<id>/

This patch is to validate the zram functionality. Test interacts with block
device /dev/zram<id> and sysfs nodes /sys/block/zram<id>/

zram.sh: sanity check of CONFIG_ZRAM and to run zram01 and zram02 tests
zram01.sh: creates general purpose ram disks with different filesystems
zram02.sh: creates block device for swap
zram_lib.sh: create library with initialization/cleanup functions
README: ZRAM introduction and Kconfig required.
Makefile: To run zram tests

zram test output
-----------------
./zram.sh
--------------------
running zram tests
--------------------
/dev/zram0 device file found: OK
set max_comp_streams to zram device(s)
/sys/block/zram0/max_comp_streams = '2' (1/1)
zram max streams: OK
test that we can set compression algorithm
supported algs: [lzo] lz4
/sys/block/zram0/comp_algorithm = 'lzo' (1/1)
zram set compression algorithm: OK
set disk size to zram device(s)
/sys/block/zram0/disksize = '2097152' (1/1)
zram set disksizes: OK
set memory limit to zram device(s)
/sys/block/zram0/mem_limit = '2M' (1/1)
zram set memory limit: OK
make ext4 filesystem on /dev/zram0
zram mkfs.ext4: OK
mount /dev/zram0
zram mount of zram device(s): OK
fill zram0...
zram0 can be filled with '1932' KB
zram used 3M, zram disk sizes 2097152M
zram compression ratio: 699050.66:1: OK
zram cleanup
zram01 : [PASS]

/dev/zram0 device file found: OK
set max_comp_streams to zram device(s)
/sys/block/zram0/max_comp_streams = '2' (1/1)
zram max streams: OK
set disk size to zram device(s)
/sys/block/zram0/disksize = '1048576' (1/1)
zram set disksizes: OK
set memory limit to zram device(s)
/sys/block/zram0/mem_limit = '1M' (1/1)
zram set memory limit: OK
make swap with zram device(s)
done with /dev/zram0
zram making zram mkswap and swapon: OK
zram swapoff: OK
zram cleanup
zram02 : [PASS]

CC: Shuah Khan <shuahkh@osg.samsung.com>
CC: Tyler Baker <tyler.baker@linaro.org>
CC: Milosz Wasilewski <milosz.wasilewski@linaro.org>
CC: Alexey Kodanev <alexey.kodanev@oracle.com>
Signed-off-by: Naresh Kamboju <naresh.kamboju@linaro.org>
Signed-off-by: Alexey Kodanev <alexey.kodanev@oracle.com>
Reviewed-By: Tyler Baker <tyler.baker@linaro.org>
Signed-off-by: Shuah Khan <shuahkh@osg.samsung.com>