mirror of https://github.com/proxmox/mirror_qemu
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>master
Stefan Hajnoczi
Kevin Wolf
parent
a5e3d9ef4d
commit
d9d334176c
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@ -14,7 +14,7 @@ block-obj-$(CONFIG_LINUX_AIO) += linux-aio.o
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block-nested-y += raw.o cow.o qcow.o vdi.o vmdk.o cloop.o dmg.o bochs.o vpc.o vvfat.o
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block-nested-y += qcow2.o qcow2-refcount.o qcow2-cluster.o qcow2-snapshot.o
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block-nested-y += parallels.o nbd.o blkdebug.o sheepdog.o
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block-nested-y += parallels.o nbd.o blkdebug.o sheepdog.o blkverify.o
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block-nested-$(CONFIG_WIN32) += raw-win32.o
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block-nested-$(CONFIG_POSIX) += raw-posix.o
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block-nested-$(CONFIG_CURL) += curl.o
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@ -0,0 +1,382 @@
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/*
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* Block protocol for block driver correctness testing
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*
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* Copyright (C) 2010 IBM, Corp.
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*
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* This work is licensed under the terms of the GNU GPL, version 2 or later.
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* See the COPYING file in the top-level directory.
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*/
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#include <stdarg.h>
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#include "qemu_socket.h" /* for EINPROGRESS on Windows */
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#include "block_int.h"
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typedef struct {
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BlockDriverState *test_file;
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} BDRVBlkverifyState;
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typedef struct BlkverifyAIOCB BlkverifyAIOCB;
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struct BlkverifyAIOCB {
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BlockDriverAIOCB common;
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QEMUBH *bh;
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/* Request metadata */
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bool is_write;
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int64_t sector_num;
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int nb_sectors;
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int ret; /* first completed request's result */
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unsigned int done; /* completion counter */
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bool *finished; /* completion signal for cancel */
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QEMUIOVector *qiov; /* user I/O vector */
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QEMUIOVector raw_qiov; /* cloned I/O vector for raw file */
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void *buf; /* buffer for raw file I/O */
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void (*verify)(BlkverifyAIOCB *acb);
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};
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static void blkverify_aio_cancel(BlockDriverAIOCB *blockacb)
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{
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BlkverifyAIOCB *acb = (BlkverifyAIOCB *)blockacb;
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bool finished = false;
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/* Wait until request completes, invokes its callback, and frees itself */
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acb->finished = &finished;
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while (!finished) {
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qemu_aio_wait();
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}
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}
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static AIOPool blkverify_aio_pool = {
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.aiocb_size = sizeof(BlkverifyAIOCB),
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.cancel = blkverify_aio_cancel,
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};
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static void blkverify_err(BlkverifyAIOCB *acb, const char *fmt, ...)
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{
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va_list ap;
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va_start(ap, fmt);
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fprintf(stderr, "blkverify: %s sector_num=%ld nb_sectors=%d ",
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acb->is_write ? "write" : "read", acb->sector_num,
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acb->nb_sectors);
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vfprintf(stderr, fmt, ap);
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fprintf(stderr, "\n");
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va_end(ap);
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exit(1);
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}
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/* Valid blkverify filenames look like blkverify:path/to/raw_image:path/to/image */
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static int blkverify_open(BlockDriverState *bs, const char *filename, int flags)
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{
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BDRVBlkverifyState *s = bs->opaque;
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int ret;
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char *raw, *c;
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/* Parse the blkverify: prefix */
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if (strncmp(filename, "blkverify:", strlen("blkverify:"))) {
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return -EINVAL;
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}
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filename += strlen("blkverify:");
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/* Parse the raw image filename */
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c = strchr(filename, ':');
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if (c == NULL) {
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return -EINVAL;
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}
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raw = strdup(filename);
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raw[c - filename] = '\0';
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ret = bdrv_file_open(&bs->file, raw, flags);
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free(raw);
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if (ret < 0) {
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return ret;
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}
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filename = c + 1;
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/* Open the test file */
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s->test_file = bdrv_new("");
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ret = bdrv_open(s->test_file, filename, flags, NULL);
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if (ret < 0) {
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bdrv_delete(s->test_file);
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s->test_file = NULL;
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return ret;
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}
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return 0;
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}
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static void blkverify_close(BlockDriverState *bs)
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{
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BDRVBlkverifyState *s = bs->opaque;
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bdrv_delete(s->test_file);
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s->test_file = NULL;
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}
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static void blkverify_flush(BlockDriverState *bs)
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{
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BDRVBlkverifyState *s = bs->opaque;
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/* Only flush test file, the raw file is not important */
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bdrv_flush(s->test_file);
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}
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static int64_t blkverify_getlength(BlockDriverState *bs)
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{
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BDRVBlkverifyState *s = bs->opaque;
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return bdrv_getlength(s->test_file);
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}
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/**
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* Check that I/O vector contents are identical
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*
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* @a: I/O vector
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* @b: I/O vector
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* @ret: Offset to first mismatching byte or -1 if match
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*/
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static ssize_t blkverify_iovec_compare(QEMUIOVector *a, QEMUIOVector *b)
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{
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int i;
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ssize_t offset = 0;
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assert(a->niov == b->niov);
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for (i = 0; i < a->niov; i++) {
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size_t len = 0;
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uint8_t *p = (uint8_t *)a->iov[i].iov_base;
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uint8_t *q = (uint8_t *)b->iov[i].iov_base;
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assert(a->iov[i].iov_len == b->iov[i].iov_len);
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while (len < a->iov[i].iov_len && *p++ == *q++) {
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len++;
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}
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offset += len;
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if (len != a->iov[i].iov_len) {
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return offset;
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}
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}
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return -1;
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}
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typedef struct {
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int src_index;
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struct iovec *src_iov;
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void *dest_base;
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} IOVectorSortElem;
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static int sortelem_cmp_src_base(const void *a, const void *b)
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{
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const IOVectorSortElem *elem_a = a;
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const IOVectorSortElem *elem_b = b;
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/* Don't overflow */
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if (elem_a->src_iov->iov_base < elem_b->src_iov->iov_base) {
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return -1;
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} else if (elem_a->src_iov->iov_base > elem_b->src_iov->iov_base) {
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return 1;
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} else {
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return 0;
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}
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}
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static int sortelem_cmp_src_index(const void *a, const void *b)
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{
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const IOVectorSortElem *elem_a = a;
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const IOVectorSortElem *elem_b = b;
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return elem_a->src_index - elem_b->src_index;
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}
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/**
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* Copy contents of I/O vector
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*
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* The relative relationships of overlapping iovecs are preserved. This is
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* necessary to ensure identical semantics in the cloned I/O vector.
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*/
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static void blkverify_iovec_clone(QEMUIOVector *dest, const QEMUIOVector *src,
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void *buf)
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{
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IOVectorSortElem sortelems[src->niov];
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void *last_end;
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int i;
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/* Sort by source iovecs by base address */
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for (i = 0; i < src->niov; i++) {
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sortelems[i].src_index = i;
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sortelems[i].src_iov = &src->iov[i];
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}
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qsort(sortelems, src->niov, sizeof(sortelems[0]), sortelem_cmp_src_base);
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/* Allocate buffer space taking into account overlapping iovecs */
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last_end = NULL;
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for (i = 0; i < src->niov; i++) {
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struct iovec *cur = sortelems[i].src_iov;
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ptrdiff_t rewind = 0;
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/* Detect overlap */
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if (last_end && last_end > cur->iov_base) {
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rewind = last_end - cur->iov_base;
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}
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sortelems[i].dest_base = buf - rewind;
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buf += cur->iov_len - MIN(rewind, cur->iov_len);
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last_end = MAX(cur->iov_base + cur->iov_len, last_end);
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}
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/* Sort by source iovec index and build destination iovec */
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qsort(sortelems, src->niov, sizeof(sortelems[0]), sortelem_cmp_src_index);
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for (i = 0; i < src->niov; i++) {
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qemu_iovec_add(dest, sortelems[i].dest_base, src->iov[i].iov_len);
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}
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}
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static BlkverifyAIOCB *blkverify_aio_get(BlockDriverState *bs, bool is_write,
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int64_t sector_num, QEMUIOVector *qiov,
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int nb_sectors,
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BlockDriverCompletionFunc *cb,
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void *opaque)
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{
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BlkverifyAIOCB *acb = qemu_aio_get(&blkverify_aio_pool, bs, cb, opaque);
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acb->bh = NULL;
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acb->is_write = is_write;
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acb->sector_num = sector_num;
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acb->nb_sectors = nb_sectors;
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acb->ret = -EINPROGRESS;
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acb->done = 0;
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acb->qiov = qiov;
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acb->buf = NULL;
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acb->verify = NULL;
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acb->finished = NULL;
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return acb;
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}
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static void blkverify_aio_bh(void *opaque)
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{
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BlkverifyAIOCB *acb = opaque;
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qemu_bh_delete(acb->bh);
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if (acb->buf) {
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qemu_iovec_destroy(&acb->raw_qiov);
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qemu_vfree(acb->buf);
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}
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acb->common.cb(acb->common.opaque, acb->ret);
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if (acb->finished) {
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*acb->finished = true;
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}
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qemu_aio_release(acb);
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}
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static void blkverify_aio_cb(void *opaque, int ret)
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{
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BlkverifyAIOCB *acb = opaque;
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switch (++acb->done) {
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case 1:
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acb->ret = ret;
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break;
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case 2:
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if (acb->ret != ret) {
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blkverify_err(acb, "return value mismatch %d != %d", acb->ret, ret);
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}
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if (acb->verify) {
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acb->verify(acb);
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}
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acb->bh = qemu_bh_new(blkverify_aio_bh, acb);
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qemu_bh_schedule(acb->bh);
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break;
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}
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}
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static void blkverify_verify_readv(BlkverifyAIOCB *acb)
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{
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ssize_t offset = blkverify_iovec_compare(acb->qiov, &acb->raw_qiov);
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if (offset != -1) {
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blkverify_err(acb, "contents mismatch in sector %ld",
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acb->sector_num + (offset / BDRV_SECTOR_SIZE));
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}
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}
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static BlockDriverAIOCB *blkverify_aio_readv(BlockDriverState *bs,
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int64_t sector_num, QEMUIOVector *qiov, int nb_sectors,
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BlockDriverCompletionFunc *cb, void *opaque)
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{
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BDRVBlkverifyState *s = bs->opaque;
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BlkverifyAIOCB *acb = blkverify_aio_get(bs, false, sector_num, qiov,
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nb_sectors, cb, opaque);
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acb->verify = blkverify_verify_readv;
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acb->buf = qemu_blockalign(bs->file, qiov->size);
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qemu_iovec_init(&acb->raw_qiov, acb->qiov->niov);
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blkverify_iovec_clone(&acb->raw_qiov, qiov, acb->buf);
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if (!bdrv_aio_readv(s->test_file, sector_num, qiov, nb_sectors,
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blkverify_aio_cb, acb)) {
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blkverify_aio_cb(acb, -EIO);
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}
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if (!bdrv_aio_readv(bs->file, sector_num, &acb->raw_qiov, nb_sectors,
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blkverify_aio_cb, acb)) {
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blkverify_aio_cb(acb, -EIO);
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}
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return &acb->common;
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}
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static BlockDriverAIOCB *blkverify_aio_writev(BlockDriverState *bs,
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int64_t sector_num, QEMUIOVector *qiov, int nb_sectors,
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BlockDriverCompletionFunc *cb, void *opaque)
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{
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BDRVBlkverifyState *s = bs->opaque;
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BlkverifyAIOCB *acb = blkverify_aio_get(bs, true, sector_num, qiov,
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nb_sectors, cb, opaque);
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if (!bdrv_aio_writev(s->test_file, sector_num, qiov, nb_sectors,
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blkverify_aio_cb, acb)) {
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blkverify_aio_cb(acb, -EIO);
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}
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if (!bdrv_aio_writev(bs->file, sector_num, qiov, nb_sectors,
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blkverify_aio_cb, acb)) {
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blkverify_aio_cb(acb, -EIO);
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}
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return &acb->common;
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}
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static BlockDriverAIOCB *blkverify_aio_flush(BlockDriverState *bs,
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BlockDriverCompletionFunc *cb,
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void *opaque)
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{
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BDRVBlkverifyState *s = bs->opaque;
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/* Only flush test file, the raw file is not important */
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return bdrv_aio_flush(s->test_file, cb, opaque);
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}
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static BlockDriver bdrv_blkverify = {
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.format_name = "blkverify",
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.protocol_name = "blkverify",
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.instance_size = sizeof(BDRVBlkverifyState),
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.bdrv_getlength = blkverify_getlength,
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.bdrv_file_open = blkverify_open,
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.bdrv_close = blkverify_close,
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.bdrv_flush = blkverify_flush,
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.bdrv_aio_readv = blkverify_aio_readv,
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.bdrv_aio_writev = blkverify_aio_writev,
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.bdrv_aio_flush = blkverify_aio_flush,
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};
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static void bdrv_blkverify_init(void)
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{
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bdrv_register(&bdrv_blkverify);
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}
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block_init(bdrv_blkverify_init);
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@ -0,0 +1,69 @@
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= Block driver correctness testing with blkverify =
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== Introduction ==
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This document describes how to use the blkverify protocol to test that a block
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driver is operating correctly.
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It is difficult to test and debug block drivers against real guests. Often
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processes inside the guest will crash because corrupt sectors were read as part
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of the executable. Other times obscure errors are raised by a program inside
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the guest. These issues are extremely hard to trace back to bugs in the block
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driver.
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Blkverify solves this problem by catching data corruption inside QEMU the first
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time bad data is read and reporting the disk sector that is corrupted.
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== How it works ==
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The blkverify protocol has two child block devices, the "test" device and the
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"raw" device. Read/write operations are mirrored to both devices so their
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state should always be in sync.
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The "raw" device is a raw image, a flat file, that has identical starting
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contents to the "test" image. The idea is that the "raw" device will handle
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read/write operations correctly and not corrupt data. It can be used as a
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reference for comparison against the "test" device.
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After a mirrored read operation completes, blkverify will compare the data and
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raise an error if it is not identical. This makes it possible to catch the
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first instance where corrupt data is read.
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== Example ==
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Imagine raw.img has 0xcd repeated throughout its first sector:
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$ ./qemu-io -c 'read -v 0 512' raw.img
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00000000: cd cd cd cd cd cd cd cd cd cd cd cd cd cd cd cd ................
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00000010: cd cd cd cd cd cd cd cd cd cd cd cd cd cd cd cd ................
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[...]
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000001e0: cd cd cd cd cd cd cd cd cd cd cd cd cd cd cd cd ................
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000001f0: cd cd cd cd cd cd cd cd cd cd cd cd cd cd cd cd ................
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read 512/512 bytes at offset 0
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512.000000 bytes, 1 ops; 0.0000 sec (97.656 MiB/sec and 200000.0000 ops/sec)
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And test.img is corrupt, its first sector is zeroed when it shouldn't be:
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$ ./qemu-io -c 'read -v 0 512' test.img
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00000000: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
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00000010: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
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[...]
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000001e0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
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000001f0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
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read 512/512 bytes at offset 0
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512.000000 bytes, 1 ops; 0.0000 sec (81.380 MiB/sec and 166666.6667 ops/sec)
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|
||||
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.
|
||||
Loading…
Reference in New Issue