Use procfs/blockdevice for diskstats#2072
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diskstats now use procfs/blockdevice instead of manually reading procfs. It prefers to use /sys but it will fallback to /proc if /sys fails. Although reading /sys/block/<dev>/stat is slower, /proc/diskstats have never garanteed atomicity between lines. A new option collector.diskstats.prefer-sysfs (true by default) can be used to skip /sys. Using /sys, diskstats will ignore partitions. If they are needed, /proc must be used or procfs/blockdevice must be extended. This solves issues with ambiguous names like xvda1 that that can both represent a partition in xvda or a standalone disk (Fixes prometheus#2041). If collector.diskstats.ignored-devices was changed to include partitions, collector.diskstats.prefer-sysfs must be set to false. if collector.diskstats.ignored-devices was untouched, both /proc and /sys should return the same results. With /sys as default, collector.diskstats.ignored-devices could be simplified to match only device names, not partitions. For now, partition filtering was kept and extended to match mmcblk0p[12]. The diskstats_linux_test.go was not implemented for /sys/block. Signed-off-by: Luiz Angelo Daros de Luca <luizluca@gmail.com>
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Use procfs/blockdevice for diskstats
diskstats now use procfs/blockdevice instead of manually reading
procfs. A new option collector.diskstats.prefer-sysfs (false by
default) can switch from /proc to /sys metrics. If /sys reading
fails, it will fallback to /proc.
Although reading /sys/block/<dev>/stat is slower, /proc/diskstats
have never garanteed atomicity between lines. Both /proc and /sys
data are equivalent except for partitions as procfs/blockdevice
/sys library does not include partition metrics. For now, if the
user expects to get partition metrics by changing default
ignored-devices, prefer-sysfs cannot be true.
Partition filtering was extended to match mmcblk0p[12].
The diskstats_linux_test.go was not implemented.
Signed-off-by: Luiz Angelo Daros de Luca luizluca@gmail.com