Xen devel - May 2012 - A little confusion between "tapdisk" and "tapdisk-ioemu"

Hi everyone,

as what I''ve learned form this
link<http://wiki.xensource.com/xenwiki/blktap>,
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something or dose the passage above give me the out of date information?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..



--
深渊之谜，为女神之遗物，吾等为求此物，振翅飞翔。


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