[Devel] [PATCH 2/3] target: allow to set a blkio cgroup for a backstore

[Cyrill Gorcunov]

On Sat, May 05, 2018 at 01:42:36AM +0300, Andrei Vagin wrote:
> The Block I/O (blkio) subsystem controls and monitors access to I/O on
> block devices by tasks in cgroups. With the introduced changes, a
> backstore will be like a task in a specified group.
> 
> One of interesting feature is an ability to set limits on a number of
> I/O operations and bytes per seconds.
> 
> A new attribute is added for backstores, it is called blkio_cgroup.
> 
> If we write 1 to the attribute file, a blkio cgroup from the current
> process is attached to the backstore.
> 
> If we write 0 to the attribute file, a current group will be detached
> from the backstore.
> 
> When we know a blkio cgroup the only thing, what we need to do to make it
> work, is to set this group for bio-s.
> 
> How to use:
>  # Create a test backstore
> $ targetcli
> targetcli shell version 2.1.fb46
> Copyright 2011-2013 by Datera, Inc and others.
> /backstores/block> create dev=/dev/loop0 loop0
> Created block storage object loop0 using /dev/loop0.
> /backstores/block> cd /loopback
> /loopback> create
> Created target naa.50014056fd3f341c.
> /loopback> cd naa.50014056fd3f341c/luns
> /loopback/naa...fd3f341c/luns> create /backstores/block/loop0
> Created LUN 0.
> /loopback/naa...fd3f341c/luns> exit
> 
>  # Create a test cgroup and set it to a test backstore
> $ CG_PATH=/sys/fs/cgroup/blkio/test
> $ BS_PATH=/sys/kernel/config/target/core/iblock_0/loop0/attrib/blkio_cgroup
> $ mkdir -p $CG_PATH
> $ bash -c "echo 0 > $CG_PATH/tasks && echo 1 > $BS_PATH"
> $ cat $BS_PATH
> /test
> 
>  # Set 6 MB/sec for the backstore
> $ echo "7:0 6291456" > $CG_PATH/blkio.throttle.read_bps_device
> 
>  # Check that everything work as expected
> $ dd if=/dev/sda of=/dev/null iflag=direct bs=1M count=100
> 100+0 records in
> 100+0 records out
> 104857600 bytes (105 MB, 100 MiB) copied, 16.6958 s, 6.3 MB/s
> 
> Signed-off-by: Andrei Vagin <avagin at openvz.org>
> ---
>  drivers/target/target_core_device.c  | 58 ++++++++++++++++++++++++++++++++++++
>  drivers/target/target_core_iblock.c  | 38 +++++++++++++++++++++++
>  include/target/target_core_backend.h |  4 +++
>  include/target/target_core_base.h    |  2 ++
>  4 files changed, 102 insertions(+)
> 
> diff --git a/drivers/target/target_core_device.c b/drivers/target/target_core_device.c
> index cb17aeb..fb1e940 100644
> --- a/drivers/target/target_core_device.c
> +++ b/drivers/target/target_core_device.c
> @@ -831,6 +831,58 @@ int se_dev_set_emulate_fua_read(struct se_device *dev, int flag)
>  }
>  EXPORT_SYMBOL(se_dev_set_emulate_fua_read);
>  
> +ssize_t se_dev_blkio_cgroup_show(struct se_device *dev, char *page)
> +{
> +	int rb;
> +
> +	read_lock(&dev->dev_attrib_lock);
> +	if (dev->dev_attrib.blk_css) {
> +		rb = cgroup_path(dev->dev_attrib.blk_css->cgroup,
> +						page, PAGE_SIZE - 1);
> +		if (rb == 0)
> +			rb = strlen(page);

Maybe it would worth to use strnlen(page, PAGE_SIZE - 2); here?

> +		page[rb] = '\n';
> +		page[rb + 1] = 0;
> +		rb++;
> +	} else
> +		rb = 0;
> +	read_unlock(&dev->dev_attrib_lock);
> +
> +	return rb;