[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [Xen-devel] Fix for loop mounting of readonly images
We hit an wierd edge case when booting a fullyvirt guest VM off an ISO image stored on NFS, where the hotplug scripts would fail to map the ISO to the backend. This only happened if the ISO image was marked readonly, but on a read-write NFS mount. It worked fine on a readonly NFS mount! After a little debugging appears that losetup was failing with: # mount -orw nfs1:/some/path /mnt # strace -e trace=open losetup /dev/loop0 /mnt/rhel4-i386-AS/images/boot.iso 2>&1 | grep boot.iso open("/mnt/rhel4-i386-AS/images/boot.iso", O_RDWR) = -1 EACCES (Permission denied) /mnt/rhel4-i386-AS/images/boot.iso: Permission denied When the NFS mount is mounted read-only it works, because it falls back to setting up a readonly loop device: # mount -oro nfs1:/some/path /mnt # strace -e trace=open losetup /dev/loop0 /mnt/rhel4-i386-AS/images/boot.iso 2>&1 | grep boot.iso open("/mnt/rhel4-i386-AS/images/boot.iso", O_RDWR) = -1 EROFS (Read-only file system) open("/mnt/rhel4-i386-AS/images/boot.iso", O_RDONLY) = 3 Which made me wonder - why don't we request a readonly loopdevice in the first place, given that the ISO is being exported read-only to the guest. So I'm ataching a patch to teh block hotplug scripts which will automatically pass the '-r' option to losetup if the device sharing mode is 'r' Signed-off-by: Daniel P. Berrange <berrange@xxxxxxxxxx> Regards, Dan. -- |=- Red Hat, Engineering, Emerging Technologies, Boston. +1 978 392 2496 -=| |=- Perl modules: http://search.cpan.org/~danberr/ -=| |=- Projects: http://freshmeat.net/~danielpb/ -=| |=- GnuPG: 7D3B9505 F3C9 553F A1DA 4AC2 5648 23C1 B3DF F742 7D3B 9505 -=| Attachment:
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