Re: [libvirt] [PATCH] qemu: fix use a nonexist address in qemuDomainAttachDeviceConfig

On 12/16/14 13:32, Luyao Huang wrote: > On 12/16/2014 08:00 PM, Peter Krempa wrote: >> On 12/15/14 10:10, Luyao Huang wrote: >>> We free them before, then use it. This make we always do >> We clear the pointer, not free. >> >>> virDomainDefAddImplicitControllers when attach a disk. >>> >>> Signed-off-by: Luyao Huang <lhuang(a)redhat.com&gt; >>> --- >>> src/qemu/qemu_driver.c | 2 +- >>> 1 file changed, 1 insertion(+), 1 deletion(-) >>> >>> diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c >>> index df3ba6d..a9afa5d 100644 >>> --- a/src/qemu/qemu_driver.c >>> +++ b/src/qemu/qemu_driver.c >>> @@ -7223,10 +7223,10 @@ qemuDomainAttachDeviceConfig(virQEMUCapsPtr >>> qemuCaps, >>> if (virDomainDiskInsert(vmdef, disk)) >>> return -1; >>> /* vmdef has the pointer. Generic codes for vmdef will do >>> all jobs */ >>> - dev->data.disk = NULL; >> The comment even explains why the line is there. From that point on, the >> pointer is owned by 'vmdef' and thus the original needs to be cleared so >> that it isn't freed (and doulbe freed) later on. > Oh, i see. Thanks for your review and i found seems i don't check if gdb > is real go to virDomainDefAddImplicitControllers, just check the > pointer's value is optimized out. > > (gdb) > 7204 dev->data.disk = NULL; > (gdb) > 7205 if (disk->bus != VIR_DOMAIN_DISK_BUS_VIRTIO) > (gdb) p disk > $3 = <optimized out> "optimized out" means that GDB can't access the variable as it is stored in a register or for other reason caused by the code optimizer. It does not mean that the variable is cleared or whatever, just that GDB can't print it.

Peter