Archipelago » qemu

/*

 * QEMU Enhanced Disk Format Consistency Check

 *

 * Copyright IBM, Corp. 2010

 *

 * Authors:

 *  Stefan Hajnoczi   <stefanha@linux.vnet.ibm.com>

 *

 * This work is licensed under the terms of the GNU LGPL, version 2 or later.

 * See the COPYING.LIB file in the top-level directory.

 *

 */

#include "qed.h"

typedef struct {

    BDRVQEDState *s;

    BdrvCheckResult *result;

    bool fix;                           /* whether to fix invalid offsets */

    uint64_t nclusters;

    uint32_t *used_clusters;            /* referenced cluster bitmap */

    QEDRequest request;

} QEDCheck;

static bool qed_test_bit(uint32_t *bitmap, uint64_t n) {

    return !!(bitmap[n / 32] & (1 << (n % 32)));

}

static void qed_set_bit(uint32_t *bitmap, uint64_t n) {

    bitmap[n / 32] |= 1 << (n % 32);

}

/**

 * Set bitmap bits for clusters

 *

 * @check:          Check structure

 * @offset:         Starting offset in bytes

 * @n:              Number of clusters

 */

static bool qed_set_used_clusters(QEDCheck *check, uint64_t offset,

                                  unsigned int n)

{

    uint64_t cluster = qed_bytes_to_clusters(check->s, offset);

    unsigned int corruptions = 0;

    while (n-- != 0) {

        /* Clusters should only be referenced once */

        if (qed_test_bit(check->used_clusters, cluster)) {

            corruptions++;

        }

        qed_set_bit(check->used_clusters, cluster);

        cluster++;

    }

    check->result->corruptions += corruptions;

    return corruptions == 0;

}

/**

 * Check an L2 table

 *

 * @ret:            Number of invalid cluster offsets

 */

static unsigned int qed_check_l2_table(QEDCheck *check, QEDTable *table)

{

    BDRVQEDState *s = check->s;

    unsigned int i, num_invalid = 0;

    uint64_t last_offset = 0;

    for (i = 0; i < s->table_nelems; i++) {

        uint64_t offset = table->offsets[i];

        if (qed_offset_is_unalloc_cluster(offset) ||

            qed_offset_is_zero_cluster(offset)) {

            continue;

        }

        check->result->bfi.allocated_clusters++;

        if (last_offset && (last_offset + s->header.cluster_size != offset)) {

            check->result->bfi.fragmented_clusters++;

        }

        last_offset = offset;

        /* Detect invalid cluster offset */

        if (!qed_check_cluster_offset(s, offset)) {

            if (check->fix) {

                table->offsets[i] = 0;

                check->result->corruptions_fixed++;

            } else {

                check->result->corruptions++;

            }

            num_invalid++;

            continue;

        }

        qed_set_used_clusters(check, offset, 1);

    }

    return num_invalid;

}

/**

 * Descend tables and check each cluster is referenced once only

 */

static int qed_check_l1_table(QEDCheck *check, QEDTable *table)

{

    BDRVQEDState *s = check->s;

    unsigned int i, num_invalid_l1 = 0;

    int ret, last_error = 0;

    /* Mark L1 table clusters used */

    qed_set_used_clusters(check, s->header.l1_table_offset,

                          s->header.table_size);

    for (i = 0; i < s->table_nelems; i++) {

        unsigned int num_invalid_l2;

        uint64_t offset = table->offsets[i];

        if (qed_offset_is_unalloc_cluster(offset)) {

            continue;

        }

        /* Detect invalid L2 offset */

        if (!qed_check_table_offset(s, offset)) {

            /* Clear invalid offset */

            if (check->fix) {

                table->offsets[i] = 0;

                check->result->corruptions_fixed++;

            } else {

                check->result->corruptions++;

            }

            num_invalid_l1++;

            continue;

        }

        if (!qed_set_used_clusters(check, offset, s->header.table_size)) {

            continue; /* skip an invalid table */

        }

        ret = qed_read_l2_table_sync(s, &check->request, offset);

        if (ret) {

            check->result->check_errors++;

            last_error = ret;

            continue;

        }

        num_invalid_l2 = qed_check_l2_table(check,

                                            check->request.l2_table->table);

        /* Write out fixed L2 table */

        if (num_invalid_l2 > 0 && check->fix) {

            ret = qed_write_l2_table_sync(s, &check->request, 0,

                                          s->table_nelems, false);

            if (ret) {

                check->result->check_errors++;

                last_error = ret;

                continue;

            }

        }

    }

    /* Drop reference to final table */

    qed_unref_l2_cache_entry(check->request.l2_table);

    check->request.l2_table = NULL;

    /* Write out fixed L1 table */

    if (num_invalid_l1 > 0 && check->fix) {

        ret = qed_write_l1_table_sync(s, 0, s->table_nelems);

        if (ret) {

            check->result->check_errors++;

            last_error = ret;

        }

    }

    return last_error;

}

/**

 * Check for unreferenced (leaked) clusters

 */

static void qed_check_for_leaks(QEDCheck *check)

{

    BDRVQEDState *s = check->s;

    uint64_t i;

    for (i = s->header.header_size; i < check->nclusters; i++) {

        if (!qed_test_bit(check->used_clusters, i)) {

            check->result->leaks++;

        }

    }

}

/**

 * Mark an image clean once it passes check or has been repaired

 */

static void qed_check_mark_clean(BDRVQEDState *s, BdrvCheckResult *result)

{

    /* Skip if there were unfixable corruptions or I/O errors */

    if (result->corruptions > 0 || result->check_errors > 0) {

        return;

    }

    /* Skip if image is already marked clean */

    if (!(s->header.features & QED_F_NEED_CHECK)) {

        return;

    }

    /* Ensure fixes reach storage before clearing check bit */

    bdrv_flush(s->bs);

    s->header.features &= ~QED_F_NEED_CHECK;

    qed_write_header_sync(s);

}

int qed_check(BDRVQEDState *s, BdrvCheckResult *result, bool fix)

{

    QEDCheck check = {

        .s = s,

        .result = result,

        .nclusters = qed_bytes_to_clusters(s, s->file_size),

        .request = { .l2_table = NULL },

        .fix = fix,

    };

    int ret;

    check.used_clusters = g_malloc0(((check.nclusters + 31) / 32) *

                                       sizeof(check.used_clusters[0]));

    check.result->bfi.total_clusters =

        (s->header.image_size + s->header.cluster_size - 1) /

            s->header.cluster_size;

    ret = qed_check_l1_table(&check, s->l1_table);

    if (ret == 0) {

        /* Only check for leaks if entire image was scanned successfully */

        qed_check_for_leaks(&check);

        if (fix) {

            qed_check_mark_clean(s, result);

        }

    }

    g_free(check.used_clusters);

    return ret;

}