On Wed, Apr 16, 2014 at 08:53:27AM +0800, Qu Wenruo wrote:
> >So the problem is not that btrfs is fast enough ;-)
> According to your explaination, it seems that if there is any modification
> to the block device, libblkid will rescan it and not
> to use the old cache, do I understand it right?
Yes, blkid_verify():
if (now >= dev->bid_time &&
#ifdef HAVE_STRUCT_STAT_ST_MTIM_TV_NSEC
(st.st_mtime < dev->bid_time ||
(st.st_mtime == dev->bid_time &&
st.st_mtim.tv_nsec / 1000 <= dev->bid_utime)) &&
#else
st.st_mtime <= dev->bid_time &&
#endif
(diff < BLKID_PROBE_MIN ||
(dev->bid_flags & BLKID_BID_FL_VERIFIED &&
diff < BLKID_PROBE_INTERVAL)))
return dev;
It checks two basic things:
a) compare device st_mtime with cache entry time (bid_time and bid_utime),
the valid cache entry has not to be older than device mtime.
b) valid cache entry has not to be older than BLKID_PROBE_MIN (2 sec)
and previous blkid_verify() validation remaining in memory has not
to be older than BLKID_PROBE_INTERVAL (200s).
> >BTW, it would be nice to have --verbose option for btrfs-scan, now it
> >seems like black box.
> I'd like to add it, but as you know, 'btrfs dev scan' just calls a btrfs
> ioctl, so even '--verbose' is added,
> nothing useful will be printed out. :(
Well, I mean at least info about for what devices it calls the ioctls.
Karel
--
Karel Zak <kzak@xxxxxxxxxx>
http://karelzak.blogspot.com
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