Re: [Qemu-devel] [PATCH v5 2/6] add basic backup support to block driver

[Markus Armbruster]

First pass, fairly superficial, hope it helps anyway.

Dietmar Maurer <address@hidden> writes:

> Function backup_job_create() creates a block job to backup a block device.
> The coroutine is started with backup_job_start().
>
> We call backup_do_cow() for each write during backup. That function
> reads the original data and pass it to backup_dump_cb().
>
> The tracked_request infrastructure is used to serialize access.
>
> Currently backup cluster size is hardcoded to 65536 bytes.
>
> Signed-off-by: Dietmar Maurer <address@hidden>
> ---
>  Makefile.objs            |    1 +
>  backup.c                 |  355 
> ++++++++++++++++++++++++++++++++++++++++++++++
>  backup.h                 |   30 ++++
>  block.c                  |   71 +++++++++-
>  include/block/block.h    |    2 +
>  include/block/blockjob.h |   10 ++
>  6 files changed, 463 insertions(+), 6 deletions(-)
>  create mode 100644 backup.c
>  create mode 100644 backup.h
>
> diff --git a/Makefile.objs b/Makefile.objs
> index a68cdac..df64f70 100644
> --- a/Makefile.objs
> +++ b/Makefile.objs
> @@ -13,6 +13,7 @@ block-obj-$(CONFIG_POSIX) += aio-posix.o
>  block-obj-$(CONFIG_WIN32) += aio-win32.o
>  block-obj-y += block/
>  block-obj-y += qapi-types.o qapi-visit.o
> +block-obj-y += backup.o
>  
>  block-obj-y += qemu-coroutine.o qemu-coroutine-lock.o qemu-coroutine-io.o
>  block-obj-y += qemu-coroutine-sleep.o
> diff --git a/backup.c b/backup.c
> new file mode 100644
> index 0000000..8955e1a
> --- /dev/null
> +++ b/backup.c
> @@ -0,0 +1,355 @@
> +/*
> + * QEMU backup
> + *
> + * Copyright (C) 2013 Proxmox Server Solutions
> + *
> + * Authors:
> + *  Dietmar Maurer (address@hidden)
> + *
> + * 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 "block/block.h"
> +#include "block/block_int.h"
> +#include "block/blockjob.h"
> +#include "qemu/ratelimit.h"
> +#include "backup.h"
> +
> +#define DEBUG_BACKUP 0
> +
> +#define USE_ALLOCATION_CHECK 0

What's this, and when would you want to enable it?

> +
> +#define DPRINTF(fmt, ...) \
> +    do { if (DEBUG_BACKUP) { printf("backup: " fmt, ## __VA_ARGS__); } } \
> +    while (0)

Have you considered tracepoints?

> +
> +
> +#define SLICE_TIME 100000000ULL /* ns */
> +
> +typedef struct BackupBlockJob {
> +    BlockJob common;
> +    RateLimit limit;
> +    CoRwlock rwlock;
> +    uint64_t sectors_read;
> +    unsigned long *bitmap;
> +    int bitmap_size;
> +    BackupDumpFunc *backup_dump_cb;
> +    BlockDriverCompletionFunc *backup_complete_cb;
> +    void *opaque;
> +} BackupBlockJob;
> +
> +static bool backup_get_bitmap(BackupBlockJob *job, int64_t cluster_num)
> +{
> +    assert(job);
> +    assert(job->bitmap);
> +
> +    unsigned long val, idx, bit;
> +
> +    idx = cluster_num / BITS_PER_LONG;
> +
> +    assert(job->bitmap_size > idx);
> +
> +    bit = cluster_num % BITS_PER_LONG;
> +    val = job->bitmap[idx];
> +
> +    return !!(val & (1UL << bit));
> +}

Sure you can't use our bitmap helpers and need to roll your own?  Have a
look at include/qemu/bitops.h and include/qemu/bitmap.h.

> +
> +static void backup_set_bitmap(BackupBlockJob *job, int64_t cluster_num,
> +                              bool dirty)
> +{
> +    assert(job);
> +    assert(job->bitmap);
> +
> +    unsigned long val, idx, bit;
> +
> +    idx = cluster_num / BITS_PER_LONG;
> +
> +    assert(job->bitmap_size > idx);
> +
> +    bit = cluster_num % BITS_PER_LONG;
> +    val = job->bitmap[idx];
> +    if (dirty) {
> +        val |= 1UL << bit;
> +    } else {
> +        val &= ~(1UL << bit);
> +    }
> +    job->bitmap[idx] = val;
> +}
> +
> +static int coroutine_fn backup_do_cow(BlockDriverState *bs,
> +                                      int64_t sector_num, int nb_sectors)
> +{
> +    assert(bs);
> +    BackupBlockJob *job = (BackupBlockJob *)bs->job;
> +    assert(job);
> +
> +    BlockDriver *drv = bs->drv;
> +    struct iovec iov;
> +    QEMUIOVector bounce_qiov;
> +    void *bounce_buffer = NULL;
> +    int ret = 0;
> +
> +    qemu_co_rwlock_rdlock(&job->rwlock);
> +
> +    int64_t start, end;
> +
> +    start = sector_num / BACKUP_BLOCKS_PER_CLUSTER;
> +    end = (sector_num + nb_sectors + BACKUP_BLOCKS_PER_CLUSTER - 1) /
> +        BACKUP_BLOCKS_PER_CLUSTER;

Looks similar to round_to_job_clusters().

> +
> +    DPRINTF("brdv_co_backup_cow enter %s C%" PRId64 " %" PRId64 " %d\n",
> +            bdrv_get_device_name(bs), start, sector_num, nb_sectors);
> +
> +    for (; start < end; start++) {
> +        bool zero = 0;
> +
> +        if (backup_get_bitmap(job, start)) {
> +            DPRINTF("brdv_co_backup_cow skip C%" PRId64 "\n", start);
> +            continue; /* already copied */
> +        }
> +
> +        /* immediately set bitmap (avoid coroutine race) */
> +        backup_set_bitmap(job, start, 1);
> +
> +        DPRINTF("brdv_co_backup_cow C%" PRId64 "\n", start);
> +
> +        if (!bounce_buffer) {
> +            iov.iov_len = BACKUP_CLUSTER_SIZE;
> +            iov.iov_base = bounce_buffer = qemu_blockalign(bs, iov.iov_len);

Naive question: why must bounce_buffer be aligned?

> +            qemu_iovec_init_external(&bounce_qiov, &iov, 1);
> +        }
> +
> +#if USE_ALLOCATION_CHECK
> +        int n = 0;
> +        ret = bdrv_co_is_allocated_above(bs, NULL,
> +                                         start * BACKUP_BLOCKS_PER_CLUSTER,
> +                                         BACKUP_BLOCKS_PER_CLUSTER, &n);
> +        if (ret < 0) {
> +            DPRINTF("brdv_co_backup_cow is_allocated C%" PRId64 " failed\n",
> +                    start);
> +            goto out;
> +        }
> +
> +        zero = (ret == 0) && (n == BACKUP_BLOCKS_PER_CLUSTER);
> +
> +        if (!zero) {
> +#endif
> +            ret = drv->bdrv_co_readv(bs, start * BACKUP_BLOCKS_PER_CLUSTER,
> +                                     BACKUP_BLOCKS_PER_CLUSTER,
> +                                     &bounce_qiov);
> +            if (ret < 0) {
> +                DPRINTF("brdv_co_backup_cow bdrv_read C%" PRId64 " failed\n",
> +                        start);
> +                goto out;
> +            }
> +#if USE_ALLOCATION_CHECK
> +        }
> +#endif
> +        job->sectors_read += BACKUP_BLOCKS_PER_CLUSTER;
> +
> +        ret = job->backup_dump_cb(job->opaque, bs, start,
> +                                  zero ? NULL : bounce_buffer);
> +        if (ret < 0) {
> +            DPRINTF("brdv_co_backup_cow dump_cluster_cb C%" PRId64 " 
> failed\n",
> +                    start);
> +            goto out;
> +        }
> +
> +        DPRINTF("brdv_co_backup_cow done C%" PRId64 "\n", start);
> +    }
> +
> +out:
> +    if (bounce_buffer) {
> +        qemu_vfree(bounce_buffer);
> +    }
> +
> +    qemu_co_rwlock_unlock(&job->rwlock);
> +
> +    return ret;
> +}
> +
> +static int coroutine_fn backup_before_read(BlockDriverState *bs,
> +                                           int64_t sector_num,
> +                                           int nb_sectors, QEMUIOVector 
> *qiov)
> +{
> +    return backup_do_cow(bs, sector_num, nb_sectors);
> +}
> +
> +static int coroutine_fn backup_before_write(BlockDriverState *bs,
> +                                            int64_t sector_num,
> +                                            int nb_sectors, QEMUIOVector 
> *qiov)
> +{
> +    return backup_do_cow(bs, sector_num, nb_sectors);
> +}
> +
> +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 BlockJobType backup_job_type = {
> +    .instance_size = sizeof(BackupBlockJob),
> +    .before_read = backup_before_read,
> +    .before_write = backup_before_write,
> +    .job_type = "backup",
> +    .set_speed = backup_set_speed,
> +};
> +
> +static void coroutine_fn backup_run(void *opaque)
> +{
> +    BackupBlockJob *job = opaque;
> +    BlockDriverState *bs = job->common.bs;
> +    assert(bs);
> +
> +    int64_t start, end;
> +
> +    start = 0;
> +    end = (bs->total_sectors + BACKUP_BLOCKS_PER_CLUSTER - 1) /
> +        BACKUP_BLOCKS_PER_CLUSTER;
> +
> +    DPRINTF("backup_run start %s %" PRId64 " %" PRId64 "\n",
> +            bdrv_get_device_name(bs), start, end);
> +
> +    int ret = 0;
> +
> +    for (; start < end; start++) {
> +        if (block_job_is_cancelled(&job->common)) {
> +            ret = -1;
> +            break;
> +        }
> +
> +        /* we need to yield so that qemu_aio_flush() returns.
> +         * (without, VM does not reboot)
> +         * Note: use 1000 instead of 0 (0 prioritize this task too much)
> +         */
> +        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, rt_clock, delay_ns);
> +        } else {
> +            block_job_sleep_ns(&job->common, rt_clock, 1000);
> +        }

Magic number 1000.  How did you arrive at that value?

> +
> +        if (block_job_is_cancelled(&job->common)) {
> +            ret = -1;
> +            break;
> +        }
> +
> +        if (backup_get_bitmap(job, start)) {
> +            continue; /* already copied */
> +        }
> +
> +        DPRINTF("backup_run loop C%" PRId64 "\n", start);
> +
> +        /**
> +         * This triggers a cluster copy
> +         * Note: avoid direct call to brdv_co_backup_cow, because
> +         * this does not call tracked_request_begin()
> +         */
> +        ret = bdrv_co_backup(bs, start*BACKUP_BLOCKS_PER_CLUSTER, 1);
> +        if (ret < 0) {
> +            break;
> +        }
> +        /* Publish progress */
> +        job->common.offset += BACKUP_CLUSTER_SIZE;
> +    }
> +
> +    /* wait until pending backup_do_cow()calls have completed */
> +    qemu_co_rwlock_wrlock(&job->rwlock);
> +    qemu_co_rwlock_unlock(&job->rwlock);
> +
> +    DPRINTF("backup_run complete %d\n", ret);
> +    block_job_completed(&job->common, ret);
> +}
> +
> +static void backup_job_cleanup_cb(void *opaque, int ret)
> +{
> +    BlockDriverState *bs = opaque;
> +    assert(bs);
> +    BackupBlockJob *job = (BackupBlockJob *)bs->job;
> +    assert(job);
> +
> +    DPRINTF("backup_job_cleanup_cb start %d\n", ret);
> +
> +    job->backup_complete_cb(job->opaque, ret);
> +
> +    DPRINTF("backup_job_cleanup_cb end\n");
> +
> +    g_free(job->bitmap);
> +}
> +
> +void
> +backup_job_start(BlockDriverState *bs, bool cancel)
> +{
> +    assert(bs);
> +    assert(bs->job);
> +    assert(bs->job->co == NULL);
> +
> +    if (cancel) {
> +        block_job_cancel(bs->job); /* set cancel flag */
> +    }
> +
> +    bs->job->co = qemu_coroutine_create(backup_run);
> +    qemu_coroutine_enter(bs->job->co, bs->job);
> +}
> +
> +int
> +backup_job_create(BlockDriverState *bs, BackupDumpFunc *backup_dump_cb,
> +                  BlockDriverCompletionFunc *backup_complete_cb,
> +                  void *opaque, int64_t speed)
> +{
> +    assert(bs);
> +    assert(backup_dump_cb);
> +    assert(backup_complete_cb);
> +
> +    if (bs->job) {
> +        DPRINTF("bdrv_backup_init failed - running job on %s\n",
> +                bdrv_get_device_name(bs));
> +        return -1;
> +    }
> +
> +    int64_t bitmap_size;
> +    const char *devname = bdrv_get_device_name(bs);
> +
> +    if (!devname || !devname[0]) {
> +        return -1;
> +    }
> +
> +    DPRINTF("bdrv_backup_init %s\n", bdrv_get_device_name(bs));
> +
> +    Error *errp;
> +    BackupBlockJob *job = block_job_create(&backup_job_type, bs, speed,
> +                                           backup_job_cleanup_cb, bs, &errp);
> +
> +    qemu_co_rwlock_init(&job->rwlock);
> +
> +    job->common.cluster_size = BACKUP_CLUSTER_SIZE;
> +
> +    bitmap_size = bs->total_sectors +
> +        BACKUP_BLOCKS_PER_CLUSTER * BITS_PER_LONG - 1;
> +    bitmap_size /= BACKUP_BLOCKS_PER_CLUSTER * BITS_PER_LONG;
> +
> +    job->backup_dump_cb = backup_dump_cb;
> +    job->backup_complete_cb = backup_complete_cb;
> +    job->opaque = opaque;
> +    job->bitmap_size = bitmap_size;
> +    job->bitmap = g_new0(unsigned long, bitmap_size);
> +
> +    job->common.len = bs->total_sectors*BDRV_SECTOR_SIZE;

Spaces around * please.

> +
> +    return 0;
> +}
> diff --git a/backup.h b/backup.h
> new file mode 100644
> index 0000000..9b1ea1c
> --- /dev/null
> +++ b/backup.h
> @@ -0,0 +1,30 @@
> +/*
> + * QEMU backup related definitions
> + *
> + * Copyright (C) 2013 Proxmox Server Solutions
> + *
> + * Authors:
> + *  Dietmar Maurer (address@hidden)
> + *
> + * This work is licensed under the terms of the GNU GPL, version 2 or later.
> + * See the COPYING file in the top-level directory.
> + *
> + */
> +
> +#ifndef QEMU_BACKUP_H
> +#define QEMU_BACKUP_H
> +
> +#define BACKUP_CLUSTER_BITS 16
> +#define BACKUP_CLUSTER_SIZE (1<<BACKUP_CLUSTER_BITS)
> +#define BACKUP_BLOCKS_PER_CLUSTER (BACKUP_CLUSTER_SIZE/BDRV_SECTOR_SIZE)
> +
> +typedef int BackupDumpFunc(void *opaque, BlockDriverState *bs,
> +                           int64_t cluster_num, unsigned char *buf);
> +
> +void backup_job_start(BlockDriverState *bs, bool cancel);
> +
> +int backup_job_create(BlockDriverState *bs, BackupDumpFunc *backup_dump_cb,
> +                      BlockDriverCompletionFunc *backup_complete_cb,
> +                      void *opaque, int64_t speed);
> +
> +#endif /* QEMU_BACKUP_H */
> diff --git a/block.c b/block.c
> index 50dab8e..6e6d08f 100644
> --- a/block.c
> +++ b/block.c
> @@ -54,6 +54,7 @@
>  typedef enum {
>      BDRV_REQ_COPY_ON_READ = 0x1,
>      BDRV_REQ_ZERO_WRITE   = 0x2,
> +    BDRV_REQ_BACKUP_ONLY  = 0x4,
>  } BdrvRequestFlags;
>  
>  static void bdrv_dev_change_media_cb(BlockDriverState *bs, bool load);
> @@ -1554,7 +1555,7 @@ int bdrv_commit(BlockDriverState *bs)
>  
>      if (!drv)
>          return -ENOMEDIUM;
> -    
> +
>      if (!bs->backing_hd) {
>          return -ENOTSUP;
>      }

Unrelated whitespace cleanup.  Separate patch or drop.

> @@ -1691,6 +1692,22 @@ void bdrv_round_to_clusters(BlockDriverState *bs,
>      }
>  }
>  
> +/**
> + * Round a region to job cluster boundaries
> + */
> +static void round_to_job_clusters(BlockDriverState *bs,
> +                                  int64_t sector_num, int nb_sectors,
> +                                  int job_cluster_size,
> +                                  int64_t *cluster_sector_num,
> +                                  int *cluster_nb_sectors)
> +{
> +    int64_t c = job_cluster_size/BDRV_SECTOR_SIZE;
> +
> +    *cluster_sector_num = QEMU_ALIGN_DOWN(sector_num, c);
> +    *cluster_nb_sectors = QEMU_ALIGN_UP(sector_num - *cluster_sector_num +
> +                                        nb_sectors, c);
> +}
> +
>  static bool tracked_request_overlaps(BdrvTrackedRequest *req,
>                                       int64_t sector_num, int nb_sectors) {
>      /*        aaaa   bbbb */
> @@ -1705,7 +1722,9 @@ static bool tracked_request_overlaps(BdrvTrackedRequest 
> *req,
>  }
>  
>  static void coroutine_fn wait_for_overlapping_requests(BlockDriverState *bs,
> -        int64_t sector_num, int nb_sectors)
> +                                                       int64_t sector_num,
> +                                                       int nb_sectors,
> +                                                       int job_cluster_size)
>  {
>      BdrvTrackedRequest *req;
>      int64_t cluster_sector_num;

Just add your parameter, no need to reformat the argument list.

> @@ -1721,6 +1740,11 @@ static void coroutine_fn 
> wait_for_overlapping_requests(BlockDriverState *bs,
>      bdrv_round_to_clusters(bs, sector_num, nb_sectors,
>                             &cluster_sector_num, &cluster_nb_sectors);
>  
> +    if (job_cluster_size) {
> +        round_to_job_clusters(bs, sector_num, nb_sectors, job_cluster_size,
> +                              &cluster_sector_num, &cluster_nb_sectors);
> +    }
> +
>      do {
>          retry = false;
>          QLIST_FOREACH(req, &bs->tracked_requests, list) {
> @@ -2260,12 +2284,24 @@ static int coroutine_fn 
> bdrv_co_do_readv(BlockDriverState *bs,
>          bs->copy_on_read_in_flight++;
>      }
>  
> -    if (bs->copy_on_read_in_flight) {
> -        wait_for_overlapping_requests(bs, sector_num, nb_sectors);
> +    int job_cluster_size = bs->job && bs->job->cluster_size ?
> +        bs->job->cluster_size : 0;
> +
> +    if (bs->copy_on_read_in_flight || job_cluster_size) {
> +        wait_for_overlapping_requests(bs, sector_num, nb_sectors,
> +                                      job_cluster_size);
>      }
>  
>      tracked_request_begin(&req, bs, sector_num, nb_sectors, false);
>  
> +    if (bs->job && bs->job->job_type->before_read) {
> +        ret = bs->job->job_type->before_read(bs, sector_num, nb_sectors, 
> qiov);
> +        if ((ret < 0) || (flags & BDRV_REQ_BACKUP_ONLY)) {
> +            /* Note: We do not return any data to the caller */
> +            goto out;
> +        }
> +    }
> +
>      if (flags & BDRV_REQ_COPY_ON_READ) {
>          int pnum;
>  
> @@ -2309,6 +2345,17 @@ int coroutine_fn 
> bdrv_co_copy_on_readv(BlockDriverState *bs,
>                              BDRV_REQ_COPY_ON_READ);
>  }
>  
> +int coroutine_fn bdrv_co_backup(BlockDriverState *bs,
> +    int64_t sector_num, int nb_sectors)
> +{
> +    if (!bs->job) {
> +        return -ENOTSUP;
> +    }
> +
> +    return bdrv_co_do_readv(bs, sector_num, nb_sectors, NULL,
> +                            BDRV_REQ_BACKUP_ONLY);
> +}
> +
>  static int coroutine_fn bdrv_co_do_write_zeroes(BlockDriverState *bs,
>      int64_t sector_num, int nb_sectors)
>  {
> @@ -2366,12 +2413,23 @@ static int coroutine_fn 
> bdrv_co_do_writev(BlockDriverState *bs,
>          bdrv_io_limits_intercept(bs, true, nb_sectors);
>      }
>  
> -    if (bs->copy_on_read_in_flight) {
> -        wait_for_overlapping_requests(bs, sector_num, nb_sectors);
> +    int job_cluster_size = bs->job && bs->job->cluster_size ?
> +        bs->job->cluster_size : 0;

Declaration not at beginning of block.

> +
> +    if (bs->copy_on_read_in_flight || job_cluster_size) {
> +        wait_for_overlapping_requests(bs, sector_num, nb_sectors,
> +                                      job_cluster_size);
>      }
>  
>      tracked_request_begin(&req, bs, sector_num, nb_sectors, true);
>  
> +    if (bs->job && bs->job->job_type->before_write) {
> +        ret = bs->job->job_type->before_write(bs, sector_num, nb_sectors, 
> qiov);
> +        if (ret < 0) {
> +            goto out;
> +        }
> +    }
> +
>      if (flags & BDRV_REQ_ZERO_WRITE) {
>          ret = bdrv_co_do_write_zeroes(bs, sector_num, nb_sectors);
>      } else {
> @@ -2390,6 +2448,7 @@ static int coroutine_fn 
> bdrv_co_do_writev(BlockDriverState *bs,
>          bs->wr_highest_sector = sector_num + nb_sectors - 1;
>      }
>  
> +out:
>      tracked_request_end(&req);
>  
>      return ret;
> diff --git a/include/block/block.h b/include/block/block.h
> index 5c3b911..b6144be 100644
> --- a/include/block/block.h
> +++ b/include/block/block.h
> @@ -172,6 +172,8 @@ int coroutine_fn bdrv_co_readv(BlockDriverState *bs, 
> int64_t sector_num,
>      int nb_sectors, QEMUIOVector *qiov);
>  int coroutine_fn bdrv_co_copy_on_readv(BlockDriverState *bs,
>      int64_t sector_num, int nb_sectors, QEMUIOVector *qiov);
> +int coroutine_fn bdrv_co_backup(BlockDriverState *bs,
> +    int64_t sector_num, int nb_sectors);
>  int coroutine_fn bdrv_co_writev(BlockDriverState *bs, int64_t sector_num,
>      int nb_sectors, QEMUIOVector *qiov);
>  /*
> diff --git a/include/block/blockjob.h b/include/block/blockjob.h
> index c290d07..6f42495 100644
> --- a/include/block/blockjob.h
> +++ b/include/block/blockjob.h
> @@ -50,6 +50,13 @@ typedef struct BlockJobType {
>       * manually.
>       */
>      void (*complete)(BlockJob *job, Error **errp);
> +
> +    /** tracked requests */
> +    int coroutine_fn (*before_read)(BlockDriverState *bs, int64_t sector_num,
> +                                    int nb_sectors, QEMUIOVector *qiov);
> +    int coroutine_fn (*before_write)(BlockDriverState *bs, int64_t 
> sector_num,
> +                                     int nb_sectors, QEMUIOVector *qiov);
> +

Comment should explain meaning of the callbacks.

>  } BlockJobType;
>  
>  /**
> @@ -103,6 +110,9 @@ struct BlockJob {
>      /** Speed that was set with @block_job_set_speed.  */
>      int64_t speed;
>  
> +    /** tracked requests */
> +    int cluster_size;
> +

Comment should explain what the variable does.

>      /** The completion function that will be called when the job completes.  
> */
>      BlockDriverCompletionFunc *cb;