blkverify: Add block driver for verifying I/O

The blkverify block driver makes investigating image format data
corruption much easier.  A raw image initialized with the same contents
as the test image (e.g. qcow2 file) must be provided.  The raw image
mirrors read/write operations and is used to verify that data read from
the test image is correct.

See docs/blkverify.txt for more information.

Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Stefan Hajnoczi 2010-09-21 15:43:03 +01:00 committed by Kevin Wolf
parent a5e3d9ef4d
commit d9d334176c
3 changed files with 452 additions and 1 deletions

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@ -14,7 +14,7 @@ block-obj-$(CONFIG_LINUX_AIO) += linux-aio.o
block-nested-y += raw.o cow.o qcow.o vdi.o vmdk.o cloop.o dmg.o bochs.o vpc.o vvfat.o
block-nested-y += qcow2.o qcow2-refcount.o qcow2-cluster.o qcow2-snapshot.o
block-nested-y += parallels.o nbd.o blkdebug.o sheepdog.o
block-nested-y += parallels.o nbd.o blkdebug.o sheepdog.o blkverify.o
block-nested-$(CONFIG_WIN32) += raw-win32.o
block-nested-$(CONFIG_POSIX) += raw-posix.o
block-nested-$(CONFIG_CURL) += curl.o

382
block/blkverify.c Normal file
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@ -0,0 +1,382 @@
/*
* Block protocol for block driver correctness testing
*
* Copyright (C) 2010 IBM, Corp.
*
* This work is licensed under the terms of the GNU GPL, version 2 or later.
* See the COPYING file in the top-level directory.
*/
#include <stdarg.h>
#include "qemu_socket.h" /* for EINPROGRESS on Windows */
#include "block_int.h"
typedef struct {
BlockDriverState *test_file;
} BDRVBlkverifyState;
typedef struct BlkverifyAIOCB BlkverifyAIOCB;
struct BlkverifyAIOCB {
BlockDriverAIOCB common;
QEMUBH *bh;
/* Request metadata */
bool is_write;
int64_t sector_num;
int nb_sectors;
int ret; /* first completed request's result */
unsigned int done; /* completion counter */
bool *finished; /* completion signal for cancel */
QEMUIOVector *qiov; /* user I/O vector */
QEMUIOVector raw_qiov; /* cloned I/O vector for raw file */
void *buf; /* buffer for raw file I/O */
void (*verify)(BlkverifyAIOCB *acb);
};
static void blkverify_aio_cancel(BlockDriverAIOCB *blockacb)
{
BlkverifyAIOCB *acb = (BlkverifyAIOCB *)blockacb;
bool finished = false;
/* Wait until request completes, invokes its callback, and frees itself */
acb->finished = &finished;
while (!finished) {
qemu_aio_wait();
}
}
static AIOPool blkverify_aio_pool = {
.aiocb_size = sizeof(BlkverifyAIOCB),
.cancel = blkverify_aio_cancel,
};
static void blkverify_err(BlkverifyAIOCB *acb, const char *fmt, ...)
{
va_list ap;
va_start(ap, fmt);
fprintf(stderr, "blkverify: %s sector_num=%ld nb_sectors=%d ",
acb->is_write ? "write" : "read", acb->sector_num,
acb->nb_sectors);
vfprintf(stderr, fmt, ap);
fprintf(stderr, "\n");
va_end(ap);
exit(1);
}
/* Valid blkverify filenames look like blkverify:path/to/raw_image:path/to/image */
static int blkverify_open(BlockDriverState *bs, const char *filename, int flags)
{
BDRVBlkverifyState *s = bs->opaque;
int ret;
char *raw, *c;
/* Parse the blkverify: prefix */
if (strncmp(filename, "blkverify:", strlen("blkverify:"))) {
return -EINVAL;
}
filename += strlen("blkverify:");
/* Parse the raw image filename */
c = strchr(filename, ':');
if (c == NULL) {
return -EINVAL;
}
raw = strdup(filename);
raw[c - filename] = '\0';
ret = bdrv_file_open(&bs->file, raw, flags);
free(raw);
if (ret < 0) {
return ret;
}
filename = c + 1;
/* Open the test file */
s->test_file = bdrv_new("");
ret = bdrv_open(s->test_file, filename, flags, NULL);
if (ret < 0) {
bdrv_delete(s->test_file);
s->test_file = NULL;
return ret;
}
return 0;
}
static void blkverify_close(BlockDriverState *bs)
{
BDRVBlkverifyState *s = bs->opaque;
bdrv_delete(s->test_file);
s->test_file = NULL;
}
static void blkverify_flush(BlockDriverState *bs)
{
BDRVBlkverifyState *s = bs->opaque;
/* Only flush test file, the raw file is not important */
bdrv_flush(s->test_file);
}
static int64_t blkverify_getlength(BlockDriverState *bs)
{
BDRVBlkverifyState *s = bs->opaque;
return bdrv_getlength(s->test_file);
}
/**
* Check that I/O vector contents are identical
*
* @a: I/O vector
* @b: I/O vector
* @ret: Offset to first mismatching byte or -1 if match
*/
static ssize_t blkverify_iovec_compare(QEMUIOVector *a, QEMUIOVector *b)
{
int i;
ssize_t offset = 0;
assert(a->niov == b->niov);
for (i = 0; i < a->niov; i++) {
size_t len = 0;
uint8_t *p = (uint8_t *)a->iov[i].iov_base;
uint8_t *q = (uint8_t *)b->iov[i].iov_base;
assert(a->iov[i].iov_len == b->iov[i].iov_len);
while (len < a->iov[i].iov_len && *p++ == *q++) {
len++;
}
offset += len;
if (len != a->iov[i].iov_len) {
return offset;
}
}
return -1;
}
typedef struct {
int src_index;
struct iovec *src_iov;
void *dest_base;
} IOVectorSortElem;
static int sortelem_cmp_src_base(const void *a, const void *b)
{
const IOVectorSortElem *elem_a = a;
const IOVectorSortElem *elem_b = b;
/* Don't overflow */
if (elem_a->src_iov->iov_base < elem_b->src_iov->iov_base) {
return -1;
} else if (elem_a->src_iov->iov_base > elem_b->src_iov->iov_base) {
return 1;
} else {
return 0;
}
}
static int sortelem_cmp_src_index(const void *a, const void *b)
{
const IOVectorSortElem *elem_a = a;
const IOVectorSortElem *elem_b = b;
return elem_a->src_index - elem_b->src_index;
}
/**
* Copy contents of I/O vector
*
* The relative relationships of overlapping iovecs are preserved. This is
* necessary to ensure identical semantics in the cloned I/O vector.
*/
static void blkverify_iovec_clone(QEMUIOVector *dest, const QEMUIOVector *src,
void *buf)
{
IOVectorSortElem sortelems[src->niov];
void *last_end;
int i;
/* Sort by source iovecs by base address */
for (i = 0; i < src->niov; i++) {
sortelems[i].src_index = i;
sortelems[i].src_iov = &src->iov[i];
}
qsort(sortelems, src->niov, sizeof(sortelems[0]), sortelem_cmp_src_base);
/* Allocate buffer space taking into account overlapping iovecs */
last_end = NULL;
for (i = 0; i < src->niov; i++) {
struct iovec *cur = sortelems[i].src_iov;
ptrdiff_t rewind = 0;
/* Detect overlap */
if (last_end && last_end > cur->iov_base) {
rewind = last_end - cur->iov_base;
}
sortelems[i].dest_base = buf - rewind;
buf += cur->iov_len - MIN(rewind, cur->iov_len);
last_end = MAX(cur->iov_base + cur->iov_len, last_end);
}
/* Sort by source iovec index and build destination iovec */
qsort(sortelems, src->niov, sizeof(sortelems[0]), sortelem_cmp_src_index);
for (i = 0; i < src->niov; i++) {
qemu_iovec_add(dest, sortelems[i].dest_base, src->iov[i].iov_len);
}
}
static BlkverifyAIOCB *blkverify_aio_get(BlockDriverState *bs, bool is_write,
int64_t sector_num, QEMUIOVector *qiov,
int nb_sectors,
BlockDriverCompletionFunc *cb,
void *opaque)
{
BlkverifyAIOCB *acb = qemu_aio_get(&blkverify_aio_pool, bs, cb, opaque);
acb->bh = NULL;
acb->is_write = is_write;
acb->sector_num = sector_num;
acb->nb_sectors = nb_sectors;
acb->ret = -EINPROGRESS;
acb->done = 0;
acb->qiov = qiov;
acb->buf = NULL;
acb->verify = NULL;
acb->finished = NULL;
return acb;
}
static void blkverify_aio_bh(void *opaque)
{
BlkverifyAIOCB *acb = opaque;
qemu_bh_delete(acb->bh);
if (acb->buf) {
qemu_iovec_destroy(&acb->raw_qiov);
qemu_vfree(acb->buf);
}
acb->common.cb(acb->common.opaque, acb->ret);
if (acb->finished) {
*acb->finished = true;
}
qemu_aio_release(acb);
}
static void blkverify_aio_cb(void *opaque, int ret)
{
BlkverifyAIOCB *acb = opaque;
switch (++acb->done) {
case 1:
acb->ret = ret;
break;
case 2:
if (acb->ret != ret) {
blkverify_err(acb, "return value mismatch %d != %d", acb->ret, ret);
}
if (acb->verify) {
acb->verify(acb);
}
acb->bh = qemu_bh_new(blkverify_aio_bh, acb);
qemu_bh_schedule(acb->bh);
break;
}
}
static void blkverify_verify_readv(BlkverifyAIOCB *acb)
{
ssize_t offset = blkverify_iovec_compare(acb->qiov, &acb->raw_qiov);
if (offset != -1) {
blkverify_err(acb, "contents mismatch in sector %ld",
acb->sector_num + (offset / BDRV_SECTOR_SIZE));
}
}
static BlockDriverAIOCB *blkverify_aio_readv(BlockDriverState *bs,
int64_t sector_num, QEMUIOVector *qiov, int nb_sectors,
BlockDriverCompletionFunc *cb, void *opaque)
{
BDRVBlkverifyState *s = bs->opaque;
BlkverifyAIOCB *acb = blkverify_aio_get(bs, false, sector_num, qiov,
nb_sectors, cb, opaque);
acb->verify = blkverify_verify_readv;
acb->buf = qemu_blockalign(bs->file, qiov->size);
qemu_iovec_init(&acb->raw_qiov, acb->qiov->niov);
blkverify_iovec_clone(&acb->raw_qiov, qiov, acb->buf);
if (!bdrv_aio_readv(s->test_file, sector_num, qiov, nb_sectors,
blkverify_aio_cb, acb)) {
blkverify_aio_cb(acb, -EIO);
}
if (!bdrv_aio_readv(bs->file, sector_num, &acb->raw_qiov, nb_sectors,
blkverify_aio_cb, acb)) {
blkverify_aio_cb(acb, -EIO);
}
return &acb->common;
}
static BlockDriverAIOCB *blkverify_aio_writev(BlockDriverState *bs,
int64_t sector_num, QEMUIOVector *qiov, int nb_sectors,
BlockDriverCompletionFunc *cb, void *opaque)
{
BDRVBlkverifyState *s = bs->opaque;
BlkverifyAIOCB *acb = blkverify_aio_get(bs, true, sector_num, qiov,
nb_sectors, cb, opaque);
if (!bdrv_aio_writev(s->test_file, sector_num, qiov, nb_sectors,
blkverify_aio_cb, acb)) {
blkverify_aio_cb(acb, -EIO);
}
if (!bdrv_aio_writev(bs->file, sector_num, qiov, nb_sectors,
blkverify_aio_cb, acb)) {
blkverify_aio_cb(acb, -EIO);
}
return &acb->common;
}
static BlockDriverAIOCB *blkverify_aio_flush(BlockDriverState *bs,
BlockDriverCompletionFunc *cb,
void *opaque)
{
BDRVBlkverifyState *s = bs->opaque;
/* Only flush test file, the raw file is not important */
return bdrv_aio_flush(s->test_file, cb, opaque);
}
static BlockDriver bdrv_blkverify = {
.format_name = "blkverify",
.protocol_name = "blkverify",
.instance_size = sizeof(BDRVBlkverifyState),
.bdrv_getlength = blkverify_getlength,
.bdrv_file_open = blkverify_open,
.bdrv_close = blkverify_close,
.bdrv_flush = blkverify_flush,
.bdrv_aio_readv = blkverify_aio_readv,
.bdrv_aio_writev = blkverify_aio_writev,
.bdrv_aio_flush = blkverify_aio_flush,
};
static void bdrv_blkverify_init(void)
{
bdrv_register(&bdrv_blkverify);
}
block_init(bdrv_blkverify_init);

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docs/blkverify.txt Normal file
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@ -0,0 +1,69 @@
= 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.