On 12/09/2013 08:17 PM, Stefan Hajnoczi wrote:
On Mon, Dec 09, 2013 at 02:06:21PM +0800, jun muzi wrote:
If mount a local file(disk) in two different dirctories, it is similar to the
network storage. Detecting identical "files" is still a problem.
Such as:
dd if=/dev/zero of=aa bs=1M count=10
mkfs.ext4 aa
Then mount aa to two directories.
mount aa /mnt/dir1
mount aa /mnt/dir2
(Off-topic, but you should never mount a regular file system read/write
more than once at a time. This example is wrong, it can corrupt the
file system.)
yes, I should not to mount a regular file more than once at a time. But
I just want to say the network storage will be mount more than once at a
time.
Such as :
Create a nfs server, and mount it as followings:
# mount $IP:/home/ /mnt/dir1
# mount $IP:/home/ /mnt/dir2
If create a new file named test in /mnt/dir1, /mnt/dir2 will know this
new file "test". So the linux kernel can know the file in /mnt/dir1 and
/mnt/dir2 whether it is the same file or not.
Based on above info, qemu-kvm can know whether file1 in /mnt/dir1 and
file2 in /mnt/dir2 are the same file or not. How do qemu-kvm distinguish
between file1 and file2 is the problem we should solve. To solve this
issue, maybe could refer to the linux kernel. But I don't know now.
----
How to fix this bug:
1, realpath() ---- string-only detection
2, hard/soft link. ----maybe ref
https://lists.gnu.org/archive/html/qemu-devel/2013-11/msg01840.html
3, distinguish network storage file mounted on different dir is the same
file or not.
My question was about the bug. What is the problem you are seeing and
how do you reproduce it (including the HMP commands)?
Now I am seeing is how to "distinguish network storage file mounted on
different dir is the same file or not".
Reproduce this bug using nfs mounted in different directories:
Create a nfs server, and mount it as followings:
# mount $IP:/home/ /mnt/dir1
# mount $IP:/home/ /mnt/dir2
(qemu) snapshot_blkdev drive-scsi0-0-0 /mnt/dir1/sn1
Formatting '/mnt/dir1/sn1', fmt=qcow2 size=32212254720
backing_file='/home/juli/RHEL-7.0-20131127.1.qcow2_v3'
backing_fmt='qcow2' encryption=off cluster_size=65536 lazy_refcounts=off
(qemu) snapshot_blkdev drive-scsi0-0-0 /mnt/dir2/sn1
Formatting '/mnt/dir2/sn1', fmt=qcow2 size=32212254720
backing_file='/mnt/dir1/sn1' backing_fmt='qcow2' encryption=off
cluster_size=65536 lazy_refcounts=off
(qemu) info block
drive-scsi0-0-0: removable=0 io-status=ok file=/mnt/dir2/sn1
backing_file=/mnt/dir1/sn1 backing_file_depth=2 ro=0 drv=qcow2
encrypted=0 bps=0 bps_rd=0 bps_wr=0 iops=0 iops_rd=0 iops_wr=0
drive-virtio-disk1: removable=0 io-status=ok
file=/home/juli/data_disk.qcow2_v3 ro=0 drv=qcow2 encrypted=0 bps=0
bps_rd=0 bps_wr=0 iops=0 iops_rd=0 iops_wr=0
ide1-cd0: removable=1 locked=0 tray-open=0 io-status=ok [not inserted]
floppy0: removable=1 locked=0 tray-open=0 [not inserted]
sd0: removable=1 locked=0 tray-open=0 [not inserted]
(qemu) snapshot_blkdev drive-scsi0-0-0 /mnt/dir2/sn2
Could not open '/mnt/dir2/sn1': Could not set AIO state: Too many open
files: Too many open files
Best Regards,
Jun Li
Stefan
