sg_get_disk_io_stats(3)sg_get_disk_io_stats(3)NAME
sg_get_disk_io_stats, sg_get_disk_io_stats_r,
sg_get_disk_io_stats_diff, sg_get_disk_io_stats_diff_between,
sg_free_disk_io_stats, sg_disk_io_compare_name, sg_disk_io_com‐
pare_traffic - get disk io statistics
SYNOPSIS
#include <statgrab.h>
sg_disk_io_stats *sg_get_disk_io_stats (size_t *entries);
sg_disk_io_stats *sg_get_disk_io_stats_r (size_t *entries);
sg_disk_io_stats *sg_get_disk_io_stats_diff (size_t *entries);
sg_disk_io_stats *sg_get_disk_io_stats_diff_between (const
sg_disk_io_stats *cur, const sg_disk_io_stats *last,
size_t *entries);
sg_error sg_free_disk_io_stats (sg_disk_io_stats *data);
int sg_disk_io_compare_name (const void *va, const void *vb);
int sg_disk_io_compare_traffic (const void *va, const void *vb);
DESCRIPTION
The sg_get_disk_io_stats functions provide disk I/O statistics on a per
disk basis. All get- and diff-functions take an optional entries param‐
eter, which points (when given) to a size_t to take the number of re‐
turned vector entries.
The sg_get_disk_io_stats() and sg_get_disk_io_stats_r() functions de‐
liver the I/O-statistics since the disk has been attached to the sys‐
tem. The sg_get_disk_io_stats_diff() and sg_get_disk_io_stats_diff_be‐
tween() deliver the difference between two calls of
sg_get_disk_io_stats() or sg_get_disk_io_stats_r(), respectively.
API Shortcut
┌──────────────────────────────┬────────────────────┬─────────────────────┐
│function │ returns │ data owner │
├──────────────────────────────┼────────────────────┼─────────────────────┤
│sg_get_disk_io_stats │ sg_disk_io_stats * │ libstatgrab (thread │
│ │ │ local) │
├──────────────────────────────┼────────────────────┼─────────────────────┤
│sg_get_disk_io_stats_r │ sg_disk_io_stats * │ caller │
├──────────────────────────────┼────────────────────┼─────────────────────┤
│sg_get_disk_io_stats_diff │ sg_disk_io_stats * │ libstatgrab (thread │
│ │ │ local) │
├──────────────────────────────┼────────────────────┼─────────────────────┤
│sg_get_disk_io_stats_diff_be‐ │ sg_disk_io_stats * │ caller │
│tween │ │ │
└──────────────────────────────┴────────────────────┴─────────────────────┘
sg_disk_io_stats vectors got from sg_get_disk_io_stats_r() or
sg_get_disk_io_stats_diff_between() must be freed using
sg_free_disk_io_stats() when not needed any more. The caller is respon‐
sible for doing it.
Additionally two support functions for qsort(3) are available:
sg_disk_io_compare_name() and sg_disk_io_compare_traffic().
Example
size_t entries;
sg_disk_io_stats *io_stats = NULL;
while( NULL != ( io_stats = sg_get_disk_io_stats_diff(&entries) ) ) {
/* show disks with most traffic first */
qsort( io_stats, entries, sizeof(io_stats[0]), &sg_disk_io_compare_traffic );
show_disk_io_stats( io_stats );
}
On some platforms, such as Solaris 7, the kernel value is stored in a
32bit int, so wraps around when it reaches 4GB. Other platforms, such
as Solaris 8 (and most other modern systems), hold the value in a 64bit
int, which wraps somewhere near 17 million terabytes. The
sg_get_disk_io_stats_diff() function and the
sg_get_disk_io_stats_diff_between() function care about these overflows
and try to detect overflows when the diff is calculated.
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 for the first time.
RETURN VALUES
All diskio statistics return a pointer to a structure of type
sg_disk_io_stats.
typedef struct {
char *disk_name;
unsigned long long read_bytes;
unsigned long long write_bytes;
time_t systime;
} sg_disk_io_stats;
disk_name
The name known to the operating system. (eg. on linux it might
be hda)
read_bytes
The number of bytes the disk has read.
write_bytes
The number of bytes the disk has written.
systime
The time period over which read_bytes and write_bytes were
transferred.
BUGS
sg_get_disk_io_stats_diff and sg_get_disk_io_stats_diff_between compare
two lists of disk (block device) related I/O statistics. Each entry oc‐
curring only in the second list is passed through to the resulting list
as if it would have been compared to an entry with all statistic values
set to 0. This implies, on the very first call
sg_get_disk_io_stats_diff will return the same as sg_get_disk_io_stats.
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 trans‐
ferred and the operating system wraps at 4GB, the
sg_get_disk_io_stats_diff() function will return 5GB.
The compare functions exists rather for backward compatibility than for
functionality enhancements. Limited flexibility (e.g. reverse order)
and lack of optimising opportunities for the compiler leads to the rec‐
ommendation to implement the required compare routines locally.
SEE ALSOstatgrab(3)WEBSITE
⟨http://www.i-scream.org/libstatgrab/⟩
i-scream 2013-06-07 sg_get_disk_io_stats(3)
