sg_get_disk_io_stats, sg_get_disk_io_stats_diff — get disk io statistics
#include <statgrab.h>
sg_disk_io_stats *sg_get_disk_io_stats( | entries); |
| int * | entries; |
sg_disk_io_stats *sg_get_disk_io_stats_diff( | entries); |
| int * | entries; |
Both calls take a pointer to an int, entries, which is filled with the number of disks the machine has. This is needed to know how many sg_disk_io_stats structures have been returned. A pointer is returned to the first sg_disk_io_stats.
sg_get_disk_io_stats returns the disk IO stored in the kernel which holds the amount of data transferred since bootup. On some platforms, such as Solaris 7, this value is stored in a 32bit int, so wraps around when it reaches 4GB. Other platforms, such as Solaris 8, hold the value in a 64bit int, which wraps somewhere near 17 million terabytes.
sg_get_disk_io_stats_diff is the same as sg_get_disk_io_stats except it will return the difference since the last call. So, for instance a call to sg_get_disk_io_stats_diff is made, and called again 5 seconds later. Over that time, 2000 bytes of traffic were written and 10000 bytes read. write_bytes will store 2000 bytes, read_bytes will store 10000, and systime will store 5. This function copes with wrap arounds by the O/S so should be seemless to use.
On Solaris libstatgrab will attempt to get the cXtXdXsX representation for the disk_name string. If it fails it will use a name like sd0. On some systems programs calling libstatgrab will need elevated privileges to lookup some of the names. The mappings are built up when sg_init is called.
All diskio statistics return a pointer to a structure of type sg_disk_io_stats.
typedef struct{
char *disk_name;
long long read_bytes;
long long write_bytes;
time_t systime;
}sg_disk_io_stats;
The name known to the operating system. (eg. on linux it might be hda)
The number of bytes the disk has read.
The number of bytes the disk has written.
The time period over which read_bytes and write_bytes were transferred.
On the very first call sg_get_disk_io_stats_diff will return the same as sg_get_disk_io_stats. After the first call it will always return the difference.
On operating systems that hold only 32bits of data there is a problem if the values wrap twice. For example, on Solaris 7 if 9GB is transferred and the operating system wraps at 4GB, the sg_get_disk_io_stats_diff function will return 5GB.