Archipelago » qemu

/*

 * QEMU backup

 *

 * Copyright (C) 2013 Proxmox Server Solutions

 *

 * Authors:

 *  Dietmar Maurer (dietmar@proxmox.com)

 *

 * 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 <stdio.h>

#include <errno.h>

#include <unistd.h>

#include "trace.h"

#include "block/block.h"

#include "block/block_int.h"

#include "block/blockjob.h"

#include "qemu/ratelimit.h"

#define BACKUP_CLUSTER_BITS 16

#define BACKUP_CLUSTER_SIZE (1 << BACKUP_CLUSTER_BITS)

#define BACKUP_SECTORS_PER_CLUSTER (BACKUP_CLUSTER_SIZE / BDRV_SECTOR_SIZE)

#define SLICE_TIME 100000000ULL /* ns */

typedef struct CowRequest {

    int64_t start;

    int64_t end;

    QLIST_ENTRY(CowRequest) list;

    CoQueue wait_queue; /* coroutines blocked on this request */

} CowRequest;

typedef struct BackupBlockJob {

    BlockJob common;

    BlockDriverState *target;

    MirrorSyncMode sync_mode;

    RateLimit limit;

    BlockdevOnError on_source_error;

    BlockdevOnError on_target_error;

    CoRwlock flush_rwlock;

    uint64_t sectors_read;

    HBitmap *bitmap;

    QLIST_HEAD(, CowRequest) inflight_reqs;

} BackupBlockJob;

/* See if in-flight requests overlap and wait for them to complete */

static void coroutine_fn wait_for_overlapping_requests(BackupBlockJob *job,

                                                       int64_t start,

                                                       int64_t end)

{

    CowRequest *req;

    bool retry;

    do {

        retry = false;

        QLIST_FOREACH(req, &job->inflight_reqs, list) {

            if (end > req->start && start < req->end) {

                qemu_co_queue_wait(&req->wait_queue);

                retry = true;

                break;

            }

        }

    } while (retry);

}

/* Keep track of an in-flight request */

static void cow_request_begin(CowRequest *req, BackupBlockJob *job,

                                     int64_t start, int64_t end)

{

    req->start = start;

    req->end = end;

    qemu_co_queue_init(&req->wait_queue);

    QLIST_INSERT_HEAD(&job->inflight_reqs, req, list);

}

/* Forget about a completed request */

static void cow_request_end(CowRequest *req)

{

    QLIST_REMOVE(req, list);

    qemu_co_queue_restart_all(&req->wait_queue);

}

static int coroutine_fn backup_do_cow(BlockDriverState *bs,

                                      int64_t sector_num, int nb_sectors,

                                      bool *error_is_read)

{

    BackupBlockJob *job = (BackupBlockJob *)bs->job;

    CowRequest cow_request;

    struct iovec iov;

    QEMUIOVector bounce_qiov;

    void *bounce_buffer = NULL;

    int ret = 0;

    int64_t start, end;

    int n;

    qemu_co_rwlock_rdlock(&job->flush_rwlock);

    start = sector_num / BACKUP_SECTORS_PER_CLUSTER;

    end = DIV_ROUND_UP(sector_num + nb_sectors, BACKUP_SECTORS_PER_CLUSTER);

    trace_backup_do_cow_enter(job, start, sector_num, nb_sectors);

    wait_for_overlapping_requests(job, start, end);

    cow_request_begin(&cow_request, job, start, end);

    for (; start < end; start++) {

        if (hbitmap_get(job->bitmap, start)) {

            trace_backup_do_cow_skip(job, start);

            continue; /* already copied */

        }

        trace_backup_do_cow_process(job, start);

        n = MIN(BACKUP_SECTORS_PER_CLUSTER,

                job->common.len / BDRV_SECTOR_SIZE -

                start * BACKUP_SECTORS_PER_CLUSTER);

        if (!bounce_buffer) {

            bounce_buffer = qemu_blockalign(bs, BACKUP_CLUSTER_SIZE);

        }

        iov.iov_base = bounce_buffer;

        iov.iov_len = n * BDRV_SECTOR_SIZE;

        qemu_iovec_init_external(&bounce_qiov, &iov, 1);

        ret = bdrv_co_readv(bs, start * BACKUP_SECTORS_PER_CLUSTER, n,

                            &bounce_qiov);

        if (ret < 0) {

            trace_backup_do_cow_read_fail(job, start, ret);

            if (error_is_read) {

                *error_is_read = true;

            }

            goto out;

        }

        if (buffer_is_zero(iov.iov_base, iov.iov_len)) {

            ret = bdrv_co_write_zeroes(job->target,

                                       start * BACKUP_SECTORS_PER_CLUSTER,

                                       n, BDRV_REQ_MAY_UNMAP);

        } else {

            ret = bdrv_co_writev(job->target,

                                 start * BACKUP_SECTORS_PER_CLUSTER, n,

                                 &bounce_qiov);

        }

        if (ret < 0) {

            trace_backup_do_cow_write_fail(job, start, ret);

            if (error_is_read) {

                *error_is_read = false;

            }

            goto out;

        }

        hbitmap_set(job->bitmap, start, 1);

        /* Publish progress, guest I/O counts as progress too.  Note that the

         * offset field is an opaque progress value, it is not a disk offset.

         */

        job->sectors_read += n;

        job->common.offset += n * BDRV_SECTOR_SIZE;

    }

out:

    if (bounce_buffer) {

        qemu_vfree(bounce_buffer);

    }

    cow_request_end(&cow_request);

    trace_backup_do_cow_return(job, sector_num, nb_sectors, ret);

    qemu_co_rwlock_unlock(&job->flush_rwlock);

    return ret;

}

static int coroutine_fn backup_before_write_notify(

        NotifierWithReturn *notifier,

        void *opaque)

{

    BdrvTrackedRequest *req = opaque;

    int64_t sector_num = req->offset >> BDRV_SECTOR_BITS;

    int nb_sectors = req->bytes >> BDRV_SECTOR_BITS;

    assert((req->offset & (BDRV_SECTOR_SIZE - 1)) == 0);

    assert((req->bytes & (BDRV_SECTOR_SIZE - 1)) == 0);

    return backup_do_cow(req->bs, sector_num, nb_sectors, NULL);

}

static void backup_set_speed(BlockJob *job, int64_t speed, Error **errp)

{

    BackupBlockJob *s = container_of(job, BackupBlockJob, common);

    if (speed < 0) {

        error_set(errp, QERR_INVALID_PARAMETER, "speed");

        return;

    }

    ratelimit_set_speed(&s->limit, speed / BDRV_SECTOR_SIZE, SLICE_TIME);

}

static void backup_iostatus_reset(BlockJob *job)

{

    BackupBlockJob *s = container_of(job, BackupBlockJob, common);

    bdrv_iostatus_reset(s->target);

}

static const BlockJobDriver backup_job_driver = {

    .instance_size  = sizeof(BackupBlockJob),

    .job_type       = BLOCK_JOB_TYPE_BACKUP,

    .set_speed      = backup_set_speed,

    .iostatus_reset = backup_iostatus_reset,

};

static BlockErrorAction backup_error_action(BackupBlockJob *job,

                                            bool read, int error)

{

    if (read) {

        return block_job_error_action(&job->common, job->common.bs,

                                      job->on_source_error, true, error);

    } else {

        return block_job_error_action(&job->common, job->target,

                                      job->on_target_error, false, error);

    }

}

static void coroutine_fn backup_run(void *opaque)

{

    BackupBlockJob *job = opaque;

    BlockDriverState *bs = job->common.bs;

    BlockDriverState *target = job->target;

    BlockdevOnError on_target_error = job->on_target_error;

    NotifierWithReturn before_write = {

        .notify = backup_before_write_notify,

    };

    int64_t start, end;

    int ret = 0;

    QLIST_INIT(&job->inflight_reqs);

    qemu_co_rwlock_init(&job->flush_rwlock);

    start = 0;

    end = DIV_ROUND_UP(job->common.len / BDRV_SECTOR_SIZE,

                       BACKUP_SECTORS_PER_CLUSTER);

    job->bitmap = hbitmap_alloc(end, 0);

    bdrv_set_enable_write_cache(target, true);

    bdrv_set_on_error(target, on_target_error, on_target_error);

    bdrv_iostatus_enable(target);

    bdrv_add_before_write_notifier(bs, &before_write);

    if (job->sync_mode == MIRROR_SYNC_MODE_NONE) {

        while (!block_job_is_cancelled(&job->common)) {

            /* Yield until the job is cancelled.  We just let our before_write

             * notify callback service CoW requests. */

            job->common.busy = false;

            qemu_coroutine_yield();

            job->common.busy = true;

        }

    } else {

        /* Both FULL and TOP SYNC_MODE's require copying.. */

        for (; start < end; start++) {

            bool error_is_read;

            if (block_job_is_cancelled(&job->common)) {

                break;

            }

            /* we need to yield so that qemu_aio_flush() returns.

             * (without, VM does not reboot)

             */

            if (job->common.speed) {

                uint64_t delay_ns = ratelimit_calculate_delay(

                        &job->limit, job->sectors_read);

                job->sectors_read = 0;

                block_job_sleep_ns(&job->common, QEMU_CLOCK_REALTIME, delay_ns);

            } else {

                block_job_sleep_ns(&job->common, QEMU_CLOCK_REALTIME, 0);

            }

            if (block_job_is_cancelled(&job->common)) {

                break;

            }

            if (job->sync_mode == MIRROR_SYNC_MODE_TOP) {

                int i, n;

                int alloced = 0;

                /* Check to see if these blocks are already in the

                 * backing file. */

                for (i = 0; i < BACKUP_SECTORS_PER_CLUSTER;) {

                    /* bdrv_is_allocated() only returns true/false based

                     * on the first set of sectors it comes across that

                     * are are all in the same state.

                     * For that reason we must verify each sector in the

                     * backup cluster length.  We end up copying more than

                     * needed but at some point that is always the case. */

                    alloced =

                        bdrv_is_allocated(bs,

                                start * BACKUP_SECTORS_PER_CLUSTER + i,

                                BACKUP_SECTORS_PER_CLUSTER - i, &n);

                    i += n;

                    if (alloced == 1) {

                        break;

                    }

                }

                /* If the above loop never found any sectors that are in

                 * the topmost image, skip this backup. */

                if (alloced == 0) {

                    continue;

                }

            }

            /* FULL sync mode we copy the whole drive. */

            ret = backup_do_cow(bs, start * BACKUP_SECTORS_PER_CLUSTER,

                    BACKUP_SECTORS_PER_CLUSTER, &error_is_read);

            if (ret < 0) {

                /* Depending on error action, fail now or retry cluster */

                BlockErrorAction action =

                    backup_error_action(job, error_is_read, -ret);

                if (action == BDRV_ACTION_REPORT) {

                    break;

                } else {

                    start--;

                    continue;

                }

            }

        }

    }

    notifier_with_return_remove(&before_write);

    /* wait until pending backup_do_cow() calls have completed */

    qemu_co_rwlock_wrlock(&job->flush_rwlock);

    qemu_co_rwlock_unlock(&job->flush_rwlock);

    hbitmap_free(job->bitmap);

    bdrv_iostatus_disable(target);

    bdrv_unref(target);

    block_job_completed(&job->common, ret);

}

void backup_start(BlockDriverState *bs, BlockDriverState *target,

                  int64_t speed, MirrorSyncMode sync_mode,

                  BlockdevOnError on_source_error,

                  BlockdevOnError on_target_error,

                  BlockDriverCompletionFunc *cb, void *opaque,

                  Error **errp)

{

    int64_t len;

    assert(bs);

    assert(target);

    assert(cb);

    if ((on_source_error == BLOCKDEV_ON_ERROR_STOP ||

         on_source_error == BLOCKDEV_ON_ERROR_ENOSPC) &&

        !bdrv_iostatus_is_enabled(bs)) {

        error_set(errp, QERR_INVALID_PARAMETER, "on-source-error");

        return;

    }

    len = bdrv_getlength(bs);

    if (len < 0) {

        error_setg_errno(errp, -len, "unable to get length for '%s'",

                         bdrv_get_device_name(bs));

        return;

    }

    BackupBlockJob *job = block_job_create(&backup_job_driver, bs, speed,

                                           cb, opaque, errp);

    if (!job) {

        return;

    }

    job->on_source_error = on_source_error;

    job->on_target_error = on_target_error;

    job->target = target;

    job->sync_mode = sync_mode;

    job->common.len = len;

    job->common.co = qemu_coroutine_create(backup_run);

    qemu_coroutine_enter(job->common.co, job);

}