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Description of problem:
As subject, If guest image is on NFS, discard will be invalid.
Version-Release number of selected component (if applicable):
# uname -r
3.10.0-112.el7.x86_64
qemu-kvm-rhev-1.5.3-53.el7.x86_64
How reproducible:
100%
Steps to Reproduce:
1.Boot guest and attached a data disk on NFS(/mnt/ss.raw) and enable discard
/usr/libexec/qemu-kvm -M pc -cpu Opteron_G1 -device virtio-scsi-pci,id=scsi2,indirect_desc=off,event_idx=off,bus=pci.0,addr=0x8 -drive file=/mnt/ss.raw,if=none,id=drive-hd-disk-3,media=disk,format=raw,cache=none,werror=stop,rerror=stop,discard=on -device scsi-hd,drive=drive-hd-disk-3,id=scsi_disk3 -vnc :1 -drive file=/mnt/RHEL-Server-7.0-64.qcow2,if=none,id=drive-virtio-disk,format=qcow2,cache=none,aio=native,werror=stop,rerror=stop,media=disk,discard=on,serial,copy-on-read=on,snapshot=on -device virtio-blk-pci,vectors=0,scsi=off,drive=drive-virtio-disk,id=virtio-disk,bus=pci.0,addr=0x7,bootindex=1
2.format data disk inside guest with ext4
#mkfs.ext4 /dev/sda
#mount /dev/sda /mnt
#dd if=/dev/urandom of=/mnt/test
3.check data disk image in host
# qemu-img map --output=json /mnt/ss.raw
Actual results:
{ "start": 0, "length": 20971520, "depth": 0, "zero": false, "data": true, "offset": 0}]
Expected results:
discard valib
Additional info:
If data disk image is on local(not NFS), then discard works well
The problem in QEMU is that we only try FIEMAP. The upstream proposed patches for NFS (http://thread.gmane.org/gmane.linux.nfs/59563) would use SEEK_HOLE/SEEK_DATA instead.
QEMU has code for SEEK_HOLE/SEEK_DATA, but it is not active if the OS (as is the case with Linux) supports FIEMAP. Instead, QEMU should fall back to SEEK_HOLE/SEEK_DATA if FIEMAP fails.
Hi,
from the QEMU side of things, this bug can be closed. The backport for BZ 1160237 completely removes FIEMAP from QEMU, and makes it use SEEK_HOLE/SEEK_DATA only.
Max
*** This bug has been marked as a duplicate of bug 1160237 ***
Description of problem: As subject, If guest image is on NFS, discard will be invalid. Version-Release number of selected component (if applicable): # uname -r 3.10.0-112.el7.x86_64 qemu-kvm-rhev-1.5.3-53.el7.x86_64 How reproducible: 100% Steps to Reproduce: 1.Boot guest and attached a data disk on NFS(/mnt/ss.raw) and enable discard /usr/libexec/qemu-kvm -M pc -cpu Opteron_G1 -device virtio-scsi-pci,id=scsi2,indirect_desc=off,event_idx=off,bus=pci.0,addr=0x8 -drive file=/mnt/ss.raw,if=none,id=drive-hd-disk-3,media=disk,format=raw,cache=none,werror=stop,rerror=stop,discard=on -device scsi-hd,drive=drive-hd-disk-3,id=scsi_disk3 -vnc :1 -drive file=/mnt/RHEL-Server-7.0-64.qcow2,if=none,id=drive-virtio-disk,format=qcow2,cache=none,aio=native,werror=stop,rerror=stop,media=disk,discard=on,serial,copy-on-read=on,snapshot=on -device virtio-blk-pci,vectors=0,scsi=off,drive=drive-virtio-disk,id=virtio-disk,bus=pci.0,addr=0x7,bootindex=1 2.format data disk inside guest with ext4 #mkfs.ext4 /dev/sda #mount /dev/sda /mnt #dd if=/dev/urandom of=/mnt/test 3.check data disk image in host # qemu-img map --output=json /mnt/ss.raw Actual results: { "start": 0, "length": 20971520, "depth": 0, "zero": false, "data": true, "offset": 0}] Expected results: discard valib Additional info: If data disk image is on local(not NFS), then discard works well