Re: [Qemu-devel] [PULL 00/48] ivshmem series

[Pavel Fedin]

 Hello!

 I have merged this PULL into our local repository and my colleague gave it a 
try.
 It seems to work, but looks like ivshmem + memdev + hugetlbfs doesn't do the 
right thing. Memdev does attach itself to a hugetlb, but we cannot actually 
share data with it.
 Our command line was:
--- cut ---
/usr/local/bin/qemu-system-aarch64 \
        -name ivshmem1_huge \
        -machine virt,accel=kvm,usb=off,gic-version=3 \
        -cpu host -m 2048 \
        -realtime mlock=off \
        -smp 8,sockets=8,cores=1,threads=1 \
        -nographic \
        -kernel /var/lib/libvirt/images/Image_uio \
        -append console='ttyAMA0,115200n8 root=/dev/sda4 rootwait hugepages=128 
earlycon=pl011,0x9000000' \
        -device i82801b11-bridge,id=pci.1,bus=pcie.0,addr=0x1 \
        -device pci-bridge,chassis_nr=2,id=pci.2,bus=pci.1,addr=0x1 \
        -device virtio-scsi-pci,id=scsi0,bus=pci.2,addr=0x1 \
        -drive 
file=/var/lib/libvirt/images/sda3_pool/ivshmem1_huge.qcow2,if=none,id=drive-scsi0-0-0-0,format=qcow2
 \
        -device 
scsi-hd,bus=scsi0.0,channel=0,scsi-id=0,lun=0,drive=drive-scsi0-0-0-0,id=scsi0-0-0-0,bootindex=1
 \
        -object memory-backend-file,size=4G,mem-path=/dev/huge,id=mb1,share=on \
        -device ivshmem,memdev=mb1 \
        -msg timestamp=on
--- cut ---

 The problem is that memdev creates a file as temporary, and then immediately 
unlinks it. Therefore, we cannot feed the same file to another VM. These are 
open files, used by two running VMs, which are supposed to exchange data via 
ivshmem.
--- cut ---
address@hidden igor]# ls -l /proc/34845/fd
total 0
lrwx------ 1 root root 64 Oct  9 06:59 0 -> /dev/pts/2
lrwx------ 1 root root 64 Oct  9 06:59 1 -> /dev/pts/2
...
lrwx------ 1 root root 64 Oct  9 06:59 7 -> anon_inode:[eventfd]
lrwx------ 1 root root 64 Oct  9 06:59 8 -> 
/dev/huge/qemu_back_mem._objects_mb1.lwEeDc (deleted)
lrwx------ 1 root root 64 Oct  9 06:59 9 -> /dev/kvm
address@hidden igor]# ls -l /proc/34866/fd
total 0
lrwx------ 1 root root 64 Oct  9 06:59 0 -> /dev/pts/0
lrwx------ 1 root root 64 Oct  9 06:59 1 -> /dev/pts/0
...
lrwx------ 1 root root 64 Oct  9 06:59 7 -> anon_inode:[eventfd]
lrwx------ 1 root root 64 Oct  9 06:59 8 -> 
/dev/huge/qemu_back_mem._objects_mb1.0Myp8M (deleted)
lrwx------ 1 root root 64 Oct  9 06:59 9 -> /dev/kvm
--- cut ---
 Due to the same reason, we cannot also exchange data between host and VM.
 Is it a flaw or do we just do something wrong?

Tested-by: Igor Skalkin <address@hidden>

Kind regards,
Pavel Fedin
Expert Engineer
Samsung Electronics Research center Russia