Re: [Qemu-block] [PATCH 0/8] file-posix: Make auto-read-only dynamic

[Peter Krempa]

On Fri, Mar 08, 2019 at 16:37:49 +0100, Kevin Wolf wrote:
> We introduced the auto-read-only option to fix the problem that block
> jobs that reopen a backing file read-write don't work any more when all
> nodes are created individually with -blockdev. The reason is that
> bs->file of these backing files doesn't inherit the read-only option
> from the format layer node any more if it's created separately.
> 
> The way auto-read-only was designed to fix this is that it just always
> opens the file node read-write if it can, so reopening the format layer
> node is enough to make the backing file writable when necessary.
> 
> This works in principle, but not when libvirt uses sVirt: Then QEMU
> doesn't even have the permissions to open the image file read-write
> until libvirt performs an operation where write access is needed.
> 
> This series changes auto-read-only so that it works dynamically and
> automatically reopens the file read-only or read-write depending on the
> permissions that users attached to the node requested.

While testing this series by attempting a non-active layer block-commit
I've got an assertion failure:

qemu-system-x86_64: block/file-posix.c:2715: raw_check_perm: Assertion 
`!s->perm_change_fd' failed.

Thread 1 "qemu-system-x86" received signal SIGABRT, Aborted.
0x00007f69fe08753f in raise () from target:/lib64/libc.so.6

Thread 1 (Thread 0x7f69f3b08680 (LWP 2694)):
#0  0x00007f69fe08753f in raise () from target:/lib64/libc.so.6
#1  0x00007f69fe071895 in abort () from target:/lib64/libc.so.6
#2  0x00007f69fe071769 in __assert_fail_base.cold.0 ()
   from target:/lib64/libc.so.6
#3  0x00007f69fe07f9f6 in __assert_fail () from target:/lib64/libc.so.6
#4  0x00005563cfeea7e9 in raw_check_perm (bs=0x5563d1f90100, perm=11, 
shared=21, errp=0x7fffc280c0f0) at block/file-posix.c:2715
#5  0x00005563cfe9aab4 in bdrv_check_perm (address@hidden, q=0x5563d2bd0170, 
address@hidden, cumulative_perms=11, cumulative_shared_perms=21, 
address@hidden, address@hidden) at block.c:1790
#6  0x00005563cfe9a875 in bdrv_check_update_perm (bs=0x5563d1f90100, 
q=0xbed88f135e2a5600, address@hidden, address@hidden, address@hidden, 
address@hidden, address@hidden) at block.c:1976
#7  0x00005563cfe9a9ba in bdrv_child_check_perm (address@hidden, 
address@hidden, perm=11, shared=21, ignore_children=0x7f69a47f9710, 
address@hidden, address@hidden) at block.c:1989
#8  0x00005563cfe9ab44 in bdrv_check_perm (bs=0x5563d1f943a0, address@hidden, 
q=0x5563d2bd0170, address@hidden, cumulative_perms=0, 
cumulative_shared_perms=31, address@hidden, errp=0x7fffc280c0f0, 
address@hidden) at block.c:1806
#9  0x00005563cfe9a875 in bdrv_check_update_perm (bs=0xb, q=0xbed88f135e2a5600, 
address@hidden, address@hidden, address@hidden, address@hidden, errp=0x15, 
address@hidden) at block.c:1976
#10 0x00005563cfe9a9ba in bdrv_child_check_perm (address@hidden, 
address@hidden, perm=0, shared=31, ignore_children=0x5563d1a57810, 
address@hidden, address@hidden) at block.c:1989
#11 0x00005563cfe9ab44 in bdrv_check_perm (bs=0x5563d2011320, address@hidden, 
q=0x5563d2bd0170, address@hidden, cumulative_perms=0, 
cumulative_shared_perms=6, address@hidden, errp=0x7fffc280c0f0, address@hidden) 
at block.c:1806
#12 0x00005563cfe9a875 in bdrv_check_update_perm (bs=0x0, q=0xbed88f135e2a5600, 
address@hidden, address@hidden, address@hidden, address@hidden, errp=0x1f, 
address@hidden) at block.c:1976
#13 0x00005563cfe9a9ba in bdrv_child_check_perm (address@hidden, 
address@hidden, perm=0, shared=31, ignore_children=0x5563d32dfd40, 
address@hidden, address@hidden) at block.c:1989
#14 0x00005563cfe9ab44 in bdrv_check_perm (bs=0x5563d2092340, address@hidden, 
q=0x5563d2bd0170, address@hidden, cumulative_perms=0, 
cumulative_shared_perms=6, address@hidden, errp=0x7fffc280c0f0, address@hidden) 
at block.c:1806
#15 0x00005563cfe9a875 in bdrv_check_update_perm (bs=0x0, q=0xbed88f135e2a5600, 
address@hidden, address@hidden, address@hidden, address@hidden, errp=0x1f, 
address@hidden) at block.c:1976
#16 0x00005563cfe9a9ba in bdrv_child_check_perm (address@hidden, 
address@hidden, perm=0, shared=31, ignore_children=0x5563d32dfe00, 
address@hidden, address@hidden) at block.c:1989
#17 0x00005563cfe9ab44 in bdrv_check_perm (bs=0x5563d2fea010, address@hidden, 
q=0x5563d2bd0170, address@hidden, cumulative_perms=1, 
cumulative_shared_perms=21, address@hidden, errp=0x7fffc280c0f0, 
address@hidden) at block.c:1806
#18 0x00005563cfe9a875 in bdrv_check_update_perm (bs=0x0, q=0xbed88f135e2a5600, 
address@hidden, address@hidden, address@hidden, address@hidden, errp=0x1f, 
address@hidden) at block.c:1976
#19 0x00005563cfe9a9ba in bdrv_child_check_perm (address@hidden, 
address@hidden, perm=1, shared=21, ignore_children=0x5563d32dfb40, 
address@hidden, address@hidden) at block.c:1989
#20 0x00005563cfe9ab44 in bdrv_check_perm (bs=0x5563d2113340, address@hidden, 
cumulative_perms=1, cumulative_shared_perms=21, address@hidden, address@hidden) 
at block.c:1806
#21 0x00005563cfe9f317 in bdrv_reopen_multiple (ctx=<optimized out>, 
bs_queue=0x5563d2bd0170, address@hidden) at block.c:3167
#22 0x00005563cfe9f451 in bdrv_reopen_set_read_only (address@hidden, 
address@hidden, address@hidden) at block.c:5293
#23 0x00005563cfe9f4fd in bdrv_backing_update_filename (c=<optimized out>, 
base=0x5563d1f943a0, filename=0x5563d1f943d1 "/tmp/commit0.qcow2", 
errp=0x7fffc280c0f0) at block.c:1119
#24 0x00005563cfe9f66f in bdrv_drop_intermediate (top=0x5563d2fea010, 
base=0x5563d1f943a0, backing_file_str=0x5563d1f943d1 "/tmp/commit0.qcow2") at 
block.c:4018
#25 0x00005563cfea4689 in job_prepare (job=0x5563d2539880) at job.c:771
#26 job_txn_apply (txn=<optimized out>, fn=<optimized out>) at job.c:146
#27 job_do_finalize (job=0x5563d2539880) at job.c:788
#28 0x00005563cfea4941 in job_completed_txn_success (job=0x5563d2539880) at 
job.c:842
#29 job_completed (job=0x5563d2539880) at job.c:855
#30 job_completed (job=0x5563d2539880) at job.c:846
#31 0x00005563cfea49a0 in job_exit (opaque=0x5563d2539880) at job.c:874
#32 0x00005563cff991de in aio_bh_call (bh=0x7f69a0004800) at util/async.c:118
#33 aio_bh_poll (address@hidden) at util/async.c:118
#34 0x00005563cff9c790 in aio_dispatch (ctx=0x5563d1beb7a0) at 
util/aio-posix.c:460
#35 0x00005563cff990be in aio_ctx_dispatch (source=<optimized out>, 
callback=<optimized out>, user_data=<optimized out>) at util/async.c:261
#36 0x00007f6a0013506d in g_main_context_dispatch () from 
target:/lib64/libglib-2.0.so.0
#37 0x00005563cff9b9a8 in glib_pollfds_poll () at util/main-loop.c:215
#38 os_host_main_loop_wait (timeout=<optimized out>) at util/main-loop.c:238
#39 main_loop_wait (nonblocking=<optimized out>) at util/main-loop.c:514
#40 0x00005563cfcac499 in main_loop () at vl.c:1923
#41 0x00005563cfb4c943 in main (argc=<optimized out>, argv=<optimized out>, 
envp=<optimized out>) at vl.c:4579


This is the log of QEMU monitor interactions by libvirtd:

[trimmed boring startup of qemu]
2019-03-11 12:57:10.485+0000: 3228: info : qemuMonitorIOWrite:553 : 
QEMU_MONITOR_IO_WRITE: mon=0x7fcff4027880 
buf={"execute":"cont","id":"libvirt-18"}^M
2019-03-11 12:57:10.485+0000: 3228: info : qemuMonitorJSONIOProcessLine:219 : 
QEMU_MONITOR_RECV_EVENT: mon=0x7fcff4027880 event={"timestamp": {"seconds": 
1552309030, "microseconds": 485648}, "event": "RESUME"}
2019-03-11 12:57:10.486+0000: 3228: info : qemuMonitorJSONIOProcessLine:224 : 
QEMU_MONITOR_RECV_REPLY: mon=0x7fcff4027880 reply={"return": {}, "id": 
"libvirt-18"}
2019-03-11 12:57:20.398+0000: 3243: info : qemuMonitorSend:1085 : 
QEMU_MONITOR_SEND_MSG: mon=0x7fcff4027880 
msg={"execute":"block-commit","arguments":{"device":"libvirt-2-format","job-id":"commit-vdb-libvirt-10-format","top-node":"libvirt-10-format","base-node":"libvirt-12-format","auto-finalize":true,"auto-dismiss":false},"id":"libvirt-19"}^M
2019-03-11 12:57:20.398+0000: 3228: info : qemuMonitorIOWrite:553 : 
QEMU_MONITOR_IO_WRITE: mon=0x7fcff4027880 
buf={"execute":"block-commit","arguments":{"device":"libvirt-2-format","job-id":"commit-vdb-libvirt-10-format","top-node":"libvirt-10-format","base-node":"libvirt-12-format","auto-finalize":true,"auto-dismiss":false},"id":"libvirt-19"}^M
2019-03-11 12:57:20.400+0000: 3228: info : qemuMonitorJSONIOProcessLine:219 : 
QEMU_MONITOR_RECV_EVENT: mon=0x7fcff4027880 event={"timestamp": {"seconds": 
1552309040, "microseconds": 400150}, "event": "JOB_STATUS_CHANGE", "data": 
{"status": "created", "id": "commit-vdb-libvirt-10-format"}}
2019-03-11 12:57:20.400+0000: 3228: info : qemuMonitorJSONIOProcessLine:219 : 
QEMU_MONITOR_RECV_EVENT: mon=0x7fcff4027880 event={"timestamp": {"seconds": 
1552309040, "microseconds": 400643}, "event": "JOB_STATUS_CHANGE", "data": 
{"status": "running", "id": "commit-vdb-libvirt-10-format"}}
2019-03-11 12:57:20.400+0000: 3228: info : qemuMonitorJSONIOProcessLine:224 : 
QEMU_MONITOR_RECV_REPLY: mon=0x7fcff4027880 reply={"return": {}, "id": 
"libvirt-19"}
2019-03-11 12:57:20.400+0000: 3228: info : qemuMonitorJSONIOProcessLine:219 : 
QEMU_MONITOR_RECV_EVENT: mon=0x7fcff4027880 event={"timestamp": {"seconds": 
1552309040, "microseconds": 400800}, "event": "JOB_STATUS_CHANGE", "data": 
{"status": "waiting", "id": "commit-vdb-libvirt-10-format"}}
2019-03-11 12:57:20.401+0000: 3228: info : qemuMonitorJSONIOProcessLine:219 : 
QEMU_MONITOR_RECV_EVENT: mon=0x7fcff4027880 event={"timestamp": {"seconds": 
1552309040, "microseconds": 400825}, "event": "JOB_STATUS_CHANGE", "data": 
{"status": "pending", "id": "commit-vdb-libvirt-10-format"}}
2019-03-11 12:57:20.737+0000: 3386: info : qemuMonitorClose:1007 : 
QEMU_MONITOR_CLOSE: mon=0x7fcff4027880 refs=1

The following command line was used:

LC_ALL=C \
PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin \
QEMU_AUDIO_DRV=spice \
/home/pipo/git/qemu.git/x86_64-softmmu/qemu-system-x86_64 \
-name guest=upstream-bj,debug-threads=on \
-S \
-object 
secret,id=masterKey0,format=raw,file=/var/lib/libvirt/qemu/domain-23-upstream-bj/master-key.aes
 \
-machine pc-i440fx-2.9,accel=kvm,usb=off,vmport=off,dump-guest-core=off \
-m 1000 \
-realtime mlock=off \
-smp 2,maxcpus=8,sockets=8,cores=1,threads=1 \
-object 
memory-backend-file,id=ram-node0,mem-path=/var/lib/libvirt/qemu/ram/libvirt/qemu/23-upstream-bj/ram-node0,share=yes,size=524288000,host-nodes=0,policy=bind
 \
-numa node,nodeid=0,cpus=0,cpus=2,cpus=4,cpus=6,memdev=ram-node0 \
-object 
memory-backend-file,id=ram-node1,mem-path=/var/lib/libvirt/qemu/ram/libvirt/qemu/23-upstream-bj/ram-node1,share=yes,size=524288000,host-nodes=0,policy=bind
 \
-numa node,nodeid=1,cpus=1,cpus=3,cpus=5,cpus=7,memdev=ram-node1 \
-uuid 841752b8-9452-4078-a62b-8fd9a9af011c \
-no-user-config \
-nodefaults \
-chardev socket,id=charmonitor,fd=29,server,nowait \
-mon chardev=charmonitor,id=monitor,mode=control \
-rtc base=utc,driftfix=slew \
-global kvm-pit.lost_tick_policy=delay \
-no-hpet \
-no-shutdown \
-global PIIX4_PM.disable_s3=1 \
-global PIIX4_PM.disable_s4=1 \
-boot menu=on,strict=on \
-device ich9-usb-ehci1,id=usb,bus=pci.0,addr=0x6.0x7 \
-device 
ich9-usb-uhci1,masterbus=usb.0,firstport=0,bus=pci.0,multifunction=on,addr=0x6 \
-device ich9-usb-uhci2,masterbus=usb.0,firstport=2,bus=pci.0,addr=0x6.0x1 \
-device ich9-usb-uhci3,masterbus=usb.0,firstport=4,bus=pci.0,addr=0x6.0x2 \
-device lsi,id=scsi0,bus=pci.0,addr=0x9 \
-device ahci,id=sata0,bus=pci.0,addr=0xb \
-device virtio-serial-pci,id=virtio-serial0,bus=pci.0,addr=0x5 \
-blockdev 
'{"driver":"file","filename":"/var/lib/libvirt/images/systemrescuecd-x86-4.9.5.iso","node-name":"libvirt-4-storage","auto-read-only":true,"discard":"unmap"}'
 \
-blockdev 
'{"node-name":"libvirt-4-format","read-only":true,"driver":"raw","file":"libvirt-4-storage"}'
 \
-device ide-cd,bus=ide.0,unit=0,drive=libvirt-4-format,id=ide0-0-0,bootindex=1 \
-blockdev 
'{"driver":"file","filename":"/tmp/pull0.qcow2","node-name":"libvirt-16-storage","auto-read-only":true,"discard":"unmap"}'
 \
-blockdev 
'{"node-name":"libvirt-16-format","read-only":true,"driver":"qcow2","file":"libvirt-16-storage","backing":null}'
 \
-blockdev 
'{"driver":"file","filename":"/tmp/pull1.qcow2","node-name":"libvirt-15-storage","auto-read-only":true,"discard":"unmap"}'
 \
-blockdev 
'{"node-name":"libvirt-15-format","read-only":true,"driver":"qcow2","file":"libvirt-15-storage","backing":"libvirt-16-format"}'
 \
-blockdev 
'{"driver":"file","filename":"/tmp/pull2.qcow2","node-name":"libvirt-14-storage","auto-read-only":true,"discard":"unmap"}'
 \
-blockdev 
'{"node-name":"libvirt-14-format","read-only":true,"driver":"qcow2","file":"libvirt-14-storage","backing":"libvirt-15-format"}'
 \
-blockdev 
'{"driver":"file","filename":"/tmp/pull3.qcow2","node-name":"libvirt-13-storage","auto-read-only":true,"discard":"unmap"}'
 \
-blockdev 
'{"node-name":"libvirt-13-format","read-only":true,"driver":"qcow2","file":"libvirt-13-storage","backing":"libvirt-14-format"}'
 \
-blockdev 
'{"driver":"file","filename":"/tmp/pull4.qcow2","node-name":"libvirt-3-storage","auto-read-only":true,"discard":"unmap"}'
 \
-blockdev 
'{"node-name":"libvirt-3-format","read-only":false,"driver":"qcow2","file":"libvirt-3-storage","backing":"libvirt-13-format"}'
 \
-device 
virtio-blk-pci,scsi=off,bus=pci.0,addr=0xa,drive=libvirt-3-format,id=virtio-disk0
 \
-blockdev 
'{"driver":"file","filename":"/tmp/commit0.qcow2","node-name":"libvirt-12-storage","auto-read-only":true,"discard":"unmap"}'
 \
-blockdev 
'{"node-name":"libvirt-12-format","read-only":true,"driver":"qcow2","file":"libvirt-12-storage","backing":null}'
 \
-blockdev 
'{"driver":"file","filename":"/tmp/commit1.qcow2","node-name":"libvirt-11-storage","auto-read-only":true,"discard":"unmap"}'
 \
-blockdev 
'{"node-name":"libvirt-11-format","read-only":true,"driver":"qcow2","file":"libvirt-11-storage","backing":"libvirt-12-format"}'
 \
-blockdev 
'{"driver":"file","filename":"/tmp/commit2.qcow2","node-name":"libvirt-10-storage","auto-read-only":true,"discard":"unmap"}'
 \
-blockdev 
'{"node-name":"libvirt-10-format","read-only":true,"driver":"qcow2","file":"libvirt-10-storage","backing":"libvirt-11-format"}'
 \
-blockdev 
'{"driver":"file","filename":"/tmp/commit3.qcow2","node-name":"libvirt-9-storage","auto-read-only":true,"discard":"unmap"}'
 \
-blockdev 
'{"node-name":"libvirt-9-format","read-only":true,"driver":"qcow2","file":"libvirt-9-storage","backing":"libvirt-10-format"}'
 \
-blockdev 
'{"driver":"file","filename":"/tmp/commit4.qcow2","node-name":"libvirt-2-storage","auto-read-only":true,"discard":"unmap"}'
 \
-blockdev 
'{"node-name":"libvirt-2-format","read-only":false,"driver":"qcow2","file":"libvirt-2-storage","backing":"libvirt-9-format"}'
 \
-device 
virtio-blk-pci,scsi=off,bus=pci.0,addr=0xc,drive=libvirt-2-format,id=virtio-disk1
 \
-blockdev 
'{"driver":"file","filename":"/tmp/copy0.qcow2","node-name":"libvirt-8-storage","auto-read-only":true,"discard":"unmap"}'
 \
-blockdev 
'{"node-name":"libvirt-8-format","read-only":true,"driver":"qcow2","file":"libvirt-8-storage","backing":null}'
 \
-blockdev 
'{"driver":"file","filename":"/tmp/copy1.qcow2","node-name":"libvirt-7-storage","auto-read-only":true,"discard":"unmap"}'
 \
-blockdev 
'{"node-name":"libvirt-7-format","read-only":true,"driver":"qcow2","file":"libvirt-7-storage","backing":"libvirt-8-format"}'
 \
-blockdev 
'{"driver":"file","filename":"/tmp/copy2.qcow2","node-name":"libvirt-6-storage","auto-read-only":true,"discard":"unmap"}'
 \
-blockdev 
'{"node-name":"libvirt-6-format","read-only":true,"driver":"qcow2","file":"libvirt-6-storage","backing":"libvirt-7-format"}'
 \
-blockdev 
'{"driver":"file","filename":"/tmp/copy3.qcow2","node-name":"libvirt-5-storage","auto-read-only":true,"discard":"unmap"}'
 \
-blockdev 
'{"node-name":"libvirt-5-format","read-only":true,"driver":"qcow2","file":"libvirt-5-storage","backing":"libvirt-6-format"}'
 \
-blockdev 
'{"driver":"file","filename":"/tmp/copy4.qcow2","node-name":"libvirt-1-storage","auto-read-only":true,"discard":"unmap"}'
 \
-blockdev 
'{"node-name":"libvirt-1-format","read-only":false,"driver":"qcow2","file":"libvirt-1-storage","backing":"libvirt-5-format"}'
 \
-device 
virtio-blk-pci,scsi=off,bus=pci.0,addr=0xd,drive=libvirt-1-format,id=virtio-disk2
 \
-netdev tap,fd=31,id=hostnet0,vhost=on,vhostfd=32 \
-device 
virtio-net-pci,netdev=hostnet0,id=net0,mac=52:54:00:36:bd:3b,bus=pci.0,addr=0x3 
\
-netdev tap,fd=33,id=hostnet1 \
-device 
rtl8139,netdev=hostnet1,id=net1,mac=52:54:00:2e:f1:27,bus=pci.0,addr=0x8 \
-chardev pty,id=charserial0 \
-device isa-serial,chardev=charserial0,id=serial0 \
-chardev socket,id=charchannel0,fd=34,server,nowait \
-device 
virtserialport,bus=virtio-serial0.0,nr=1,chardev=charchannel0,id=channel0,name=org.qemu.guest_agent.0
 \
-chardev spicevmc,id=charchannel1,name=vdagent \
-device 
virtserialport,bus=virtio-serial0.0,nr=2,chardev=charchannel1,id=channel1,name=com.redhat.spice.0
 \
-device usb-tablet,id=input0,bus=usb.0,port=1 \
-spice 
port=5900,addr=127.0.0.1,disable-ticketing,image-compression=off,seamless-migration=on
 \
-device 
qxl-vga,id=video0,ram_size=67108864,vram_size=67108864,vram64_size_mb=0,vgamem_mb=16,max_outputs=1,bus=pci.0,addr=0x2
 \
-device intel-hda,id=sound0,bus=pci.0,addr=0x4 \
-device hda-duplex,id=sound0-codec0,bus=sound0.0,cad=0 \
-chardev spicevmc,id=charredir0,name=usbredir \
-device usb-redir,chardev=charredir0,id=redir0,bus=usb.0,port=2 \
-chardev spicevmc,id=charredir1,name=usbredir \
-device usb-redir,chardev=charredir1,id=redir1,bus=usb.0,port=3 \
-object rng-random,id=objrng0,filename=/dev/random \
-device virtio-rng-pci,rng=objrng0,id=rng0,bus=pci.0,addr=0x7 \
-sandbox 
on,obsolete=deny,elevateprivileges=deny,spawn=deny,resourcecontrol=deny \
-msg timestamp=on

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