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

[Andrei Vagin]

On Sat, May 05, 2018 at 09:12:02AM +0300, Cyrill Gorcunov wrote:
> 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?

cgroup_path returns a null terminated string, so I don't understand a
reason for these changes.

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