mirror of
https://github.com/yuzu-emu/unicorn.git
synced 2024-12-23 19:45:29 +00:00
70 lines
3 KiB
Plaintext
70 lines
3 KiB
Plaintext
|
= Block driver correctness testing with blkverify =
|
||
|
|
|
||
|
|
== Introduction ==
|
||
|
|
|
||
|
|
This document describes how to use the blkverify protocol to test that a block
|
||
|
|
driver is operating correctly.
|
||
|
|
|
||
|
|
It is difficult to test and debug block drivers against real guests. Often
|
||
|
|
processes inside the guest will crash because corrupt sectors were read as part
|
||
|
|
of the executable. Other times obscure errors are raised by a program inside
|
||
|
|
the guest. These issues are extremely hard to trace back to bugs in the block
|
||
|
|
driver.
|
||
|
|
|
||
|
|
Blkverify solves this problem by catching data corruption inside QEMU the first
|
||
|
|
time bad data is read and reporting the disk sector that is corrupted.
|
||
|
|
|
||
|
|
== How it works ==
|
||
|
|
|
||
|
|
The blkverify protocol has two child block devices, the "test" device and the
|
||
|
|
"raw" device. Read/write operations are mirrored to both devices so their
|
||
|
|
state should always be in sync.
|
||
|
|
|
||
|
|
The "raw" device is a raw image, a flat file, that has identical starting
|
||
|
|
contents to the "test" image. The idea is that the "raw" device will handle
|
||
|
|
read/write operations correctly and not corrupt data. It can be used as a
|
||
|
|
reference for comparison against the "test" device.
|
||
|
|
|
||
|
|
After a mirrored read operation completes, blkverify will compare the data and
|
||
|
|
raise an error if it is not identical. This makes it possible to catch the
|
||
|
|
first instance where corrupt data is read.
|
||
|
|
|
||
|
|
== Example ==
|
||
|
|
|
||
|
|
Imagine raw.img has 0xcd repeated throughout its first sector:
|
||
|
|
|
||
|
|
$ ./qemu-io -c 'read -v 0 512' raw.img
|
||
|
|
00000000: cd cd cd cd cd cd cd cd cd cd cd cd cd cd cd cd ................
|
||
|
|
00000010: cd cd cd cd cd cd cd cd cd cd cd cd cd cd cd cd ................
|
||
|
|
[...]
|
||
|
|
000001e0: cd cd cd cd cd cd cd cd cd cd cd cd cd cd cd cd ................
|
||
|
|
000001f0: cd cd cd cd cd cd cd cd cd cd cd cd cd cd cd cd ................
|
||
|
|
read 512/512 bytes at offset 0
|
||
|
|
512.000000 bytes, 1 ops; 0.0000 sec (97.656 MiB/sec and 200000.0000 ops/sec)
|
||
|
|
|
||
|
|
And test.img is corrupt, its first sector is zeroed when it shouldn't be:
|
||
|
|
|
||
|
|
$ ./qemu-io -c 'read -v 0 512' test.img
|
||
|
|
00000000: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
|
||
|
|
00000010: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
|
||
|
|
[...]
|
||
|
|
000001e0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
|
||
|
|
000001f0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
|
||
|
|
read 512/512 bytes at offset 0
|
||
|
|
512.000000 bytes, 1 ops; 0.0000 sec (81.380 MiB/sec and 166666.6667 ops/sec)
|
||
|
|
|
||
|
|
This error is caught by blkverify:
|
||
|
|
|
||
|
|
$ ./qemu-io -c 'read 0 512' blkverify:a.img:b.img
|
||
|
|
blkverify: read sector_num=0 nb_sectors=4 contents mismatch in sector 0
|
||
|
|
|
||
|
|
A more realistic scenario is verifying the installation of a guest OS:
|
||
|
|
|
||
|
|
$ ./qemu-img create raw.img 16G
|
||
|
|
$ ./qemu-img create -f qcow2 test.qcow2 16G
|
||
|
|
$ x86_64-softmmu/qemu-system-x86_64 -cdrom debian.iso \
|
||
|
|
-drive file=blkverify:raw.img:test.qcow2
|
||
|
|
|
||
|
|
If the installation is aborted when blkverify detects corruption, use qemu-io
|
||
|
|
to explore the contents of the disk image at the sector in question.
|