On 04/07/2017 10:31 AM, Daniel P. Berrange wrote: > On Fri, Apr 07, 2017 at 04:27:40PM +0200, Peter Krempa wrote: >> On Fri, Apr 07, 2017 at 09:52:09 -0400, John Ferlan wrote: >>> https://bugzilla.redhat.com/show_bug.cgi?id=1439132 >>> >>> During 'matrix' testing of all possible combinations I found that if >>> device is formated with "gpt" first, then an attempt is made to format >>> using "mac", a startup will fail. By adding a clearing of the first >>> 2048 bytes of the device (similar to the logical pool code), the issue >>> is resolved. >> >> I'm not a fan of this and neither thing this is robust enough: >> >> The problem here is that apparently the "mac" table fits into the first >> block on the disk. Since the GPT disklabel is stored at LBA address 1 >> it is not overwritten at all. Thus it's apparent that the detection tool >> then prefers GPT over a older disklabel. >> >> The GPT disklabel has also a secondary copy at the last LBA of the disk. >> >> As for robustness: SECTOR_SIZE is defined as 512 in our code, thus this >> code nukes 2k of data. For devices with 4k sectors which are already >> available this won't help at all, since LBA 0 will still contain the >> protective MBR, and the 3,5k left of LBA 0 will be unused. GPT disklabel >> still will start at LBA 1. > > Personally I'd forget about sectors and just nuke 1 MB of data at start > and end of the device. The time for 2k vs 1 MB is negligible. > > OK - so I've pushed patches 4 & 5 and will rework the first 3 ... series coming soon the a mailing list near you. John -- libvir-list mailing list libvir-list@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/libvir-list
