跟踪qemu-kvm下的磁盘写入

傻了，上一个调试的时候没加-enable-kvm，而且电脑的虚拟化也是关着的。假装无事发生过，一切调整就绪后，重新在KVM模式下调试。终于在另一台linux老爷机上装好了qemu和各种软件，继续从这里来，qcow2_pre_write_overlap_check下个断点，这里的栈和TCG模式一样，继续操作，b blk_aio_prwv。

(gdb) bt
#0  qcow2_pre_write_overlap_check (bs=0x558eef1841a0, ign=0, offset=1670656, 
    size=4096, data_file=true) at block/qcow2-refcount.c:2817
#1  0x0000558eedcb12e6 in qcow2_co_pwritev_part (bs=0x558eef1841a0, 
    offset=1879080448, bytes=4096, qiov=0x7fa0e4236760, qiov_offset=0, flags=0)
    at block/qcow2.c:2513
#2  0x0000558eedcfe0de in bdrv_driver_pwritev (bs=0x558eef1841a0, 
    offset=1879080448, bytes=4096, qiov=0x7fa0e4236760, qiov_offset=0, flags=0)
    at block/io.c:1171
#3  0x0000558eedd000a5 in bdrv_aligned_pwritev (child=0x558eef191900, 
    req=0x7fa0b8acae10, offset=1879080448, bytes=4096, align=1, 
    qiov=0x7fa0e4236760, qiov_offset=0, flags=0) at block/io.c:1980
#4  0x0000558eedd0087f in bdrv_co_pwritev_part (child=0x558eef191900, 
    offset=1879080448, bytes=4096, qiov=0x7fa0e4236760, qiov_offset=0, flags=0)
    at block/io.c:2137
#5  0x0000558eedce6f6d in blk_co_pwritev_part (blk=0x558eef183e40, 
    offset=1879080448, bytes=4096, qiov=0x7fa0e4236760, qiov_offset=0, flags=0)
    at block/block-backend.c:1211
#6  0x0000558eedce6fbf in blk_co_pwritev (blk=0x558eef183e40, 
    offset=1879080448, bytes=4096, qiov=0x7fa0e4236760, flags=0)
    at block/block-backend.c:1221
#7  0x0000558eedce7795 in blk_aio_write_entry (opaque=0x7fa0e4238780)
    at block/block-backend.c:1415
#8  0x0000558eedddcc2f in coroutine_trampoline (i0=-467430144, i1=32672)
    at util/coroutine-ucontext.c:115
#9  0x00007fa0f56c8000 in ?? () from /lib/x86_64-linux-gnu/libc.so.6
#10 0x00007fa0e9cbad90 in ?? ()
#11 0x0000000000000000 in ?? ()

断下来以后，可以看到，除了上层的消息循环变成了kvm的，后面都是一样，通过直接向ioport写数据，然后转移到对应的后端处理函数中。差不多就调试完了，后面开设了一个网站督促自己读代码，qemu.world，等我想起来就更新。

(gdb) bt
#0  blk_aio_prwv (blk=0x558eef183e40, offset=0, bytes=0, iobuf=0x0, 
    co_entry=0x558eedce7a28 <blk_aio_flush_entry>, flags=0, 
    cb=0x558eedaad47c <ide_flush_cb>, opaque=0x558eefc24730)
    at block/block-backend.c:1360
#1  0x0000558eedce7ab1 in blk_aio_flush (blk=0x558eef183e40, 
    cb=0x558eedaad47c <ide_flush_cb>, opaque=0x558eefc24730)
    at block/block-backend.c:1503
#2  0x0000558eedaad5da in ide_flush_cache (s=0x558eefc24730)
    at hw/ide/core.c:1088
#3  0x0000558eedaae5b3 in cmd_flush_cache (s=0x558eefc24730, cmd=231 '\347')
    at hw/ide/core.c:1554
#4  0x0000558eedaaf8c5 in ide_exec_cmd (bus=0x558eefc246b0, val=231)
    at hw/ide/core.c:2085
#5  0x0000558eedaaddef in ide_ioport_write (opaque=0x558eefc246b0, addr=503, 
    val=231) at hw/ide/core.c:1294
#6  0x0000558eed85cd3f in portio_write (opaque=0x558eefcbff30, addr=7, 
    data=231, size=1) at /home/leon/qemu-4.2.0/ioport.c:201
#7  0x0000558eed861fbc in memory_region_write_accessor (mr=0x558eefcbff30, 
    addr=7, value=0x7fa0e9cbb818, size=1, shift=0, mask=255, attrs=...)
    at /home/leon/qemu-4.2.0/memory.c:483
#8  0x0000558eed8621a6 in access_with_adjusted_size (addr=7, 
    value=0x7fa0e9cbb818, size=1, access_size_min=1, access_size_max=4, 
    access_fn=0x558eed861efc <memory_region_write_accessor>, 
    mr=0x558eefcbff30, attrs=...) at /home/leon/qemu-4.2.0/memory.c:544
#9  0x0000558eed8650d7 in memory_region_dispatch_write (mr=0x558eefcbff30, addr=7, data=231, op=MO_8, attrs=...) at /home/leon/qemu-4.2.0/memory.c:1475
#10 0x0000558eed803386 in flatview_write_continue (fv=0x7fa0e410c970, addr=503, attrs=..., buf=0x7fa0f86ac000 "\347\200\354\036", len=1, addr1=7, l=1, mr=0x558eefcbff30) at /home/leon/qemu-4.2.0/exec.c:3129
#11 0x0000558eed8034cb in flatview_write (fv=0x7fa0e410c970, addr=503, attrs=..., buf=0x7fa0f86ac000 "\347\200\354\036", len=1) at /home/leon/qemu-4.2.0/exec.c:3169
#12 0x0000558eed803818 in address_space_write (as=0x558eee7a4b60 <address_space_io>, addr=503, attrs=..., buf=0x7fa0f86ac000 "\347\200\354\036", len=1) at /home/leon/qemu-4.2.0/exec.c:3259
#13 0x0000558eed803885 in address_space_rw (as=0x558eee7a4b60 <address_space_io>, addr=503, attrs=..., buf=0x7fa0f86ac000 "\347\200\354\036", len=1, is_write=true) at /home/leon/qemu-4.2.0/exec.c:3269
#14 0x0000558eed87cf9f in kvm_handle_io (port=503, attrs=..., data=0x7fa0f86ac000, direction=1, size=1, count=1) at /home/leon/qemu-4.2.0/accel/kvm/kvm-all.c:2104
#15 0x0000558eed87d737 in kvm_cpu_exec (cpu=0x558eef1b29b0) at /home/leon/qemu-4.2.0/accel/kvm/kvm-all.c:2350
#16 0x0000558eed853017 in qemu_kvm_cpu_thread_fn (arg=0x558eef1b29b0) at /home/leon/qemu-4.2.0/cpus.c:1318
#17 0x0000558eeddc042b in qemu_thread_start (args=0x558eef1da7e0) at util/qemu-thread-posix.c:519
#18 0x00007fa0f5a2a4a4 in start_thread () from /lib/x86_64-linux-gnu/libpthread.so.0
#19 0x00007fa0f576cd0f in clone () from /lib/x86_64-linux-gnu/libc.so.6