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Re: [Qemu-discuss] Qemu snapshot mode

From: Dunrong Huang
Subject: Re: [Qemu-discuss] Qemu snapshot mode
Date: Mon, 24 Sep 2012 10:25:17 +0800

2012/9/24 xuanmao_001 <address@hidden>:
> Hi, all
> I want to change the path of temporary snapshot file. Can you gei me some
> ideas, or tell me which file will write the  temporary snapshot file in qemu
> source code. thanks.
You should take a quick look at block.c:get_tmp_filename(),
int get_tmp_filename(char *filename, int size)
// snippet
    int fd;
    const char *tmpdir;
    tmpdir = getenv("TMPDIR");
    if (!tmpdir)
        tmpdir = "/tmp";
    if (snprintf(filename, size, "%s/vl.XXXXXX", tmpdir) >= size) {
        return -EOVERFLOW;
    fd = mkstemp(filename);
    if (fd < 0 || close(fd)) {
        return -errno;
    return 0;
So you can simply set a "TMPDIR=/var/whatyouwant" and run QEMU.
> ________________________________
> xuanmao_001
> From: Dunrong Huang
> Date: 2012-09-06 18:00
> To: xuanmao_001
> CC: qemu-discuss; Jakob Bohm
> Subject: Re: [Qemu-discuss] Qemu snapshot mode
> 2012/9/6 xuanmao_001 <address@hidden>:
>> Hi, all,
>> When I start VM with snapshot mode(--snapshot). I do some operations,like
>> copy, delete files. I must shutdown VM, the disk state can revert.
>> so I want to know if the snapshot mode can revert when I reboot VM.
> No, it cant.
> Actually, when you start QEMU with -snapshot, a temporary snapshot file
> which is not visible to the user will be created in /tmp, the file
> will exist util QEMU exit.
> So even if you reboot VM, QEMU is still running and the temporary
> snapshot also exists.
> This make you failed to convert VM after reboot.
>> Thanks.
>> ________________________________
>> xuanmao_001
> --
> Best Regards,
> Dunrong Huang

Best Regards,

Dunrong Huang

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