Red Hat Bugzilla – Bug 1259116
qemu can not read disk size of libiscsi and it shows 'disk size: unavailable'
Last modified: 2016-03-28 05:25:16 EDT
Description of problem: After formatting qcow2 image of libiscsi, the disk size shows unavailable which is not friendly to user. If this is a block device, maybe the disk size should be set 0 or other appropriate value. Version-Release number of selected component (if applicable): Host: Kernel:3.10.0-313.el7.x86_64 qemu-kvm-rhev:qemu-kvm-rhev-2.3.0-21.el7.x86_64 How reproducible: 100% Steps to Reproduce: 1. # qemu-img create -f qcow2 iscsi://10.66.9.120:3260/iqn.2003-01.org.linux-iscsi.dhcp-9-120.x8664:sn.68d22325a05a/0 20G Formatting 'iscsi://10.66.9.120:3260/iqn.2003-01.org.linux-iscsi.dhcp-9-120.x8664:sn.68d22325a05a/0', fmt=qcow2 size=21474836480 encryption=off cluster_size=65536 lazy_refcounts=off refcount_bits=16 2. # qemu-img info iscsi://10.66.9.120:3260/iqn.2003-01.org.linux-iscsi.dhcp-9-120.x8664:sn.68d22325a05a/0 image: iscsi://10.66.9.120:3260/iqn.2003-01.org.linux-iscsi.dhcp-9-120.x8664:sn.68d22325a05a/0 file format: qcow2 virtual size: 20G (21474836480 bytes) disk size: unavailable cluster_size: 65536 Format specific information: compat: 1.1 lazy refcounts: false refcount bits: 16 corrupt: false Actual results: disk size:unavailable Expected results: disk size: 0 (or other appropriate value). Additional info:
Actually I think unavailable is more accurate than "0". The allocation status can be retrieved by QEMU scanning each block in the target but that can take unnecessarily long time just to display the summary for the image. So I'm not sure this issue is worth fixing.
I agree with Fam. Alternatively, qcow2 could store a high-water mark into the header, and qemu-img info could use it. CCing Kevin for ideas, but I'm okay with CLOSED/NOTABUG.
You don't actually have to store another value in the qcow2 header. Scanning the last refcount block should be quick enough. However, I'm still not convinced whether that's useful enough to actually do it on every qcow2_open().