On Mon, Dec 15, 2008 at 22:03, Andreas Dilger <adilger@xxxxxxx> wrote: > On Dec 11, 2008 09:43 -0500, Chris Mason wrote: >> The multi-device code uses a very simple brute force scan from userland >> to populate the list of devices that belong to a given FS. Kay Sievers >> has some ideas on hotplug magic to make this less dumb. (The scan isn't >> required for single device filesystems). > > This should use libblkid to do the scanning of the devices, and it can > cache the results for efficiency. Best would be to have the same LABEL+UUID > for all devices in the same filesystem, and then once any of these devices > are found the mount.btrfs code can query the rest of the devices to find > the remaining parts of the filesystem. Which is another way to do something you should not do that way in the first place, just with a library instead of your own code. Brute-force scanning /dev with a single thread will not work reliably in many setups we need to support. Sure, it's good to have it for a rescue system, it will work fine or your workstation, but definitely not for boxes with many devices where you don't know how they behave. Just do: $ modprobe scsi_debug max_luns=8 num_parts=2 $ echo 1 > /sys/module/scsi_debug/parameters/every_nth $ echo 4 > /sys/module/scsi_debug/parameters/opts $ ls -l /sys/class/block/ | wc -l 45 and then call any binary doing /dev scanning, and wait (in this case) for ~2 hours to return. Also, the blkid cache file uses major/minor numbers or kernel device names, which will also not help in many setups we have to support today. The original btrfs topic, leading to this, is here: http://www.mail-archive.com/linux-btrfs@xxxxxxxxxxxxxxx/msg01048.html Thanks, Kay -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
