[PATCH] io-controller: do some changes of io.policy interface

[Gui Jianfeng <guijianfeng@cn.fujitsu.com>]

Paul Menage wrote:
> On Fri, Jun 19, 2009 at 1:37 PM, Vivek Goyal<vgoyal@redhat.com> wrote:
>> You can use the following format to play with the new interface.
>> #echo DEV:weight:ioprio_class > /patch/to/cgroup/policy
>> weight=0 means removing the policy for DEV.
>>
>> Examples:
>> Configure weight=300 ioprio_class=2 on /dev/hdb in this cgroup
>> # echo /dev/hdb:300:2 > io.policy
>> # cat io.policy
>> dev weight class
>> /dev/hdb 300 2
> 
> I think that the read and write should be consistent. Can you just use
> white-space separation for both, rather than colon-separation for
> writes and white-space separation for reads?
> 
> Also, storing device inode paths statically as strings into the
> io_policy structure seems wrong, since it's quite possible for the
> device node that was used originally to be gone by the time that
> someone reads the io.policy file, or renamed, or even replaced with an
> inode that refers to to a different block device
> 
> My preferred alternatives would be:
> 
> - read/write the value as a device number rather than a name
> - read/write the block device's actual name (e.g. hda or sda) rather
> than a path to the inode
> 

Hi Paul, Vivek

Here is a patch to fix the issue Paul raised.

This patch achives the following goals
1 According to Paul's comment, Modifing io.policy interface to
  use device number for read/write directly. 
2 Just use white-space separation for both, rather than colon-
  separation for writes and white-space separation for reads.
3 Do more strict checking for inputting.

old interface:
Configure weight=300 ioprio_class=2 on /dev/hdb in this cgroup
# echo "/dev/hdb:300:2" > io.policy
# cat io.policy
dev weight class
/dev/hdb 300 2

new interface:
Configure weight=300 ioprio_class=2 on /dev/hdb in this cgroup
# echo "3:64 300 2" > io.policy
# cat io.policy
dev     weight  class
3:64    300     2

Signed-off-by: Gui Jianfeng <guijianfeng@cn.fujitsu.com>
---
 block/elevator-fq.c |   59 ++++++++++++++++++++++++++++++++++----------------
 block/elevator-fq.h |    1 -
 2 files changed, 40 insertions(+), 20 deletions(-)

diff --git a/block/elevator-fq.c b/block/elevator-fq.c
index d779282..83c831b 100644
--- a/block/elevator-fq.c
+++ b/block/elevator-fq.c
@@ -1895,12 +1895,12 @@ static int io_cgroup_policy_read(struct cgroup *cgrp, struct cftype *cft,
 	if (list_empty(&iocg->policy_list))
 		goto out;
 
-	seq_printf(m, "dev weight class\n");
+	seq_printf(m, "dev\tweight\tclass\n");
 
 	spin_lock_irq(&iocg->lock);
 	list_for_each_entry(pn, &iocg->policy_list, node) {
-		seq_printf(m, "%s %lu %lu\n", pn->dev_name,
-			   pn->weight, pn->ioprio_class);
+		seq_printf(m, "%u:%u\t%lu\t%lu\n", MAJOR(pn->dev),
+			   MINOR(pn->dev), pn->weight, pn->ioprio_class);
 	}
 	spin_unlock_irq(&iocg->lock);
 out:
@@ -1936,44 +1936,65 @@ static struct io_policy_node *policy_search_node(const struct io_cgroup *iocg,
 	return NULL;
 }
 
-static int devname_to_devnum(const char *buf, dev_t *dev)
+static int check_dev_num(dev_t dev)
 {
-	struct block_device *bdev;
+	int part = 0;
 	struct gendisk *disk;
-	int part;
 
-	bdev = lookup_bdev(buf);
-	if (IS_ERR(bdev))
+	disk = get_gendisk(dev, &part);
+	if (!disk || part)
 		return -ENODEV;
 
-	disk = get_gendisk(bdev->bd_dev, &part);
-	if (part)
-		return -EINVAL;
-
-	*dev = MKDEV(disk->major, disk->first_minor);
-	bdput(bdev);
-
 	return 0;
 }
 
 static int policy_parse_and_set(char *buf, struct io_policy_node *newpn)
 {
-	char *s[3], *p;
+	char *s[4], *p, *major_s = NULL, *minor_s = NULL;
 	int ret;
+	unsigned long major, minor;
 	int i = 0;
+	dev_t dev;
 
 	memset(s, 0, sizeof(s));
-	while ((p = strsep(&buf, ":")) != NULL) {
+	while ((p = strsep(&buf, " ")) != NULL) {
 		if (!*p)
 			continue;
 		s[i++] = p;
+
+		/* Prevent from inputing too many things */
+		if (i == 4)
+			break;
 	}
 
-	ret = devname_to_devnum(s[0], &newpn->dev);
+	if (i != 3)
+		return -EINVAL;
+
+	p = strsep(&s[0], ":");
+	if (p != NULL)
+		major_s = p;
+	else
+		return -EINVAL;
+
+	minor_s = s[0];
+	if (!minor_s)
+		return -EINVAL;
+
+	ret = strict_strtoul(major_s, 10, &major);
+	if (ret)
+		return -EINVAL;
+
+	ret = strict_strtoul(minor_s, 10, &minor);
+	if (ret)
+		return -EINVAL;
+
+	dev = MKDEV(major, minor);
+
+	ret = check_dev_num(dev);
 	if (ret)
 		return ret;
 
-	strcpy(newpn->dev_name, s[0]);
+	newpn->dev = dev;
 
 	if (s[1] == NULL)
 		return -EINVAL;
diff --git a/block/elevator-fq.h b/block/elevator-fq.h
index b3193f8..7722ebe 100644
--- a/block/elevator-fq.h
+++ b/block/elevator-fq.h
@@ -286,7 +286,6 @@ struct io_group {
 
 struct io_policy_node {
 	struct list_head node;
-	char dev_name[32];
 	dev_t dev;
 	unsigned long weight;
 	unsigned long ioprio_class;
-- 
1.5.4.rc3