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Diffstat (limited to 'qemu/docs/blkverify.txt')
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diff --git a/qemu/docs/blkverify.txt b/qemu/docs/blkverify.txt deleted file mode 100644 index d556dc4e6..000000000 --- a/qemu/docs/blkverify.txt +++ /dev/null @@ -1,69 +0,0 @@ -= 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. |