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[Xen-devel] A little confusion between "tapdisk" and "tapdisk-ioemu"

Hi everyone,

as what I've learned form this link, i know that when i specify tap:aio I’m actually using the blktap driver and finally using "tapdisk" to wirite to raw image file.

but the truth is even when i delete /usr/sbin/tapdisk the domU can still boot  on my machine with tap:aio protocol

after a deeper look into the scene, i find that when i specify tap:aio the executable functioning is actually /usr/sbin/tapdisk-ioemu

i don't find enough information about the tapdisk-ioemu, am i mistaken for something or dose the passage above give me the out of date information?

I then look at the "tools/blktap/drivers/blktapctrl.c" file, I find that the code piece:

    if (!strncmp(path, "tapdisk:", strlen("tapdisk:"))) {
        *use_ioemu = 0;
        path += strlen("tapdisk:");
    } else if (!strncmp(path, "ioemu:", strlen("ioemu:"))) {
        *use_ioemu = 1;
        path += strlen("ioemu:");
    } else {
        // Use the default for the image type
        *use_ioemu = -1;

so when i specify tap:aio the value of use_ioemu is -1 right?
and the the use_ioemu var is used at:

            if (use_ioemu) {
                if (connect_qemu(blkif, blkif->domid))
                    goto fail;
            } else {
                if (connect_tapdisk(blkif, minor))
                    goto fail;

so when i use tap:aio, i finally connect_qemu witch result in the use of tapdisk-ioemu

since I wish to use the /usr/sbin/tapdisk (because i add my own code here ), i changed my disk protocol to tap:tapdisk:aio, but the domU hang while booting with following message:

[    0.185031] PCI: Fatal: No config space access function found
[    0.189998] Unable to read sysrq code in control/sysrq
[    0.350220] i8042: No controller found
[    0.452153] /home/abuild/rpmbuild/BUILD/
kernel-xen-3.1.0/linux-3.1/drivers/rtc/hctosys.c: unable to open rtc device (rtc0)

so my question is :
1, what on earth is the tapdisk-ioemu? will it replace the tapdisk?(i've seen someone metioned 'code duplication in ioemu and blktap' when i Google the word "tapdisk-ioemu")

2,How to make my tapdisk to work,

thanks ahead..

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