Statistic Module
Shuanglong Zhang
04/23/2013
Overview
• Device Mapper
• procfs
• bio control
Device Mapper
• A mechanism from linux 2.6
• The base of LVM, RAID
• dm-linear
dm-statistic
Can be infinite iteration
Don't do this!
My implementation
dm-statistic
procfs
• Used to "communicate" with user space
• /proc/statistic
• /proc/jiffies
• A drawback of procfs
Drawback
• Can not exceed one page size
• How to deal with large data
• seq_file
seq_file interface
• Deal with large data, work with procfs
• Abstract those data to a mount of items
– (array, list, hash)
• Simplify the read operation
static struct seq_operations seq_ops = {
.start = statistic_seq_start,
.next = statistic_seq_next,
.stop = statistic_seq_stop,
.show = statistic_seq_show
};
start->show->next->show->...->next->show->stop
static struct file_operations seq_fops = {
.owner
= THIS_MODULE,
.open
= statistic_open,
.read
= seq_read,
//.write
= seq_write,
.llseek
= seq_lseek,
.release = seq_release,
};
static int statistic_open(struct inode *inode,
struct file *file)
{
return (seq_open(file, &seq_ops));
}
Control on bio
• Diffrent ways to do it
– These kind of control can happen at any
stage from a request begins to it ends.
- VFS
- FS
- DM
- BLOCK
In device mapper
• A bio comes in
• Map the bio to the dest
– delay it if necessary(read, full)
– until there is another room for a bio
• Go into block layer
Delay
• Create another list for write bio
• Track back to x bios or 1 second
controled by a module parameter
• Wait till there is less then x bios in past
second
User space tool
• dmsetup
• statistic
dmsetup
• dmsetup [linear/stripe/statistic] /dev/sda10
• dmsetup remove /dev/mapper/statistic
• use sudo!
statistic
• Get the statistic info from /proc/statistic
• Two ways of querying
– last x second
– from x second to y second
• Total, Read, Write
Left Problems
• module parameter
• ioctl function(reset base_time)
• more info on bio
Demo
Q&A