Andrew Patterson wrote:
This is version 2 of a patch series I submitted back in May 2008. This version now checks for device size changes in the rescan_partitions() routine. Which in turn is called when a device is opened and in the BLKRRPART ioctl. I am resubmitting this patch series as I got little response the previous time. Al Viro has told me offline that he would look at it this time. This patch series handles online disk resizes that are currently not completely recognized by the kernel using the existing revalidate_disk routines. An online resize can occur when growing or shrinking a Fibre Channel LUN or perhaps by adding a disk to an existing RAID volume. The kernel currently recognizes a device size change when the lower-level revalidate_disk routines are called; however, the block layer does not use the new size while it has any current openers on the device. So, for example, if LVM has an volume open on the device, you will generally not see the size change until after a reboot. We fix this problem by creating a wrapper to be used with lower-level revalidate_disk routines. This wrapper first calls the lower-level driver's revalidate_disk routine. It then compares the gendisk capacity to the block devices inode size. If there is a difference, we adjust the block device's size. If the size has changed, we then flush the disk for safety. The size is also checked in rescan_partitions which is called when the device is opened or when the BLKRRPART ioctl is called. There are several ways to "kick off" a device size change: 1. For SCSI devices do: # echo 1 > /sys/class/scsi_device/<device>/device/rescan or # blockdev --rereadpt <device file> 2. Other devices (not device mapper) # blockdev --rereadpt <device file>
It would be great if you extend this functionality to automatic resizing by handling "CAPACITY DATA HAS CHANGED" Unit Attention. If necessary, I can assist in testing by adding online virtual disks resize feature together with generation of that UA in SCST (http://scst.sf.net). (It's not been implemented yet, because no known initiators so far have been able to use this feature.)
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