Re: [Qemu-devel] [PATCH v3 20/20] block: Make bdrv_is_allocated_above() byte-based

[Jeff Cody <jcody@redhat.com>]

On Tue, Jun 27, 2017 at 02:24:58PM -0500, Eric Blake wrote:
> We are gradually moving away from sector-based interfaces, towards
> byte-based.  In the common case, allocation is unlikely to ever use
> values that are not naturally sector-aligned, but it is possible
> that byte-based values will let us be more precise about allocation
> at the end of an unaligned file that can do byte-based access.
> 
> Changing the signature of the function to use int64_t *pnum ensures
> that the compiler enforces that all callers are updated.  For now,
> the io.c layer still assert()s that all callers are sector-aligned,
> but that can be relaxed when a later patch implements byte-based
> block status.  Therefore, for the most part this patch is just the
> addition of scaling at the callers followed by inverse scaling at
> bdrv_is_allocated().  But some code, particularly stream_run(),
> gets a lot simpler because it no longer has to mess with sectors.
> 
> For ease of review, bdrv_is_allocated() was tackled separately.
> 
> Signed-off-by: Eric Blake <eblake@redhat.com>
> Reviewed-by: John Snow <jsnow@redhat.com>
> 

Reviewed-by: Jeff Cody <jcody@redhat.com>

> ---
> v2: tweak function comments, favor bdrv_getlength() over ->total_sectors
> ---
>  include/block/block.h |  2 +-
>  block/commit.c        | 20 ++++++++------------
>  block/io.c            | 42 ++++++++++++++++++++----------------------
>  block/mirror.c        |  5 ++++-
>  block/replication.c   | 17 ++++++++++++-----
>  block/stream.c        | 21 +++++++++------------
>  qemu-img.c            | 10 +++++++---
>  7 files changed, 61 insertions(+), 56 deletions(-)
> 
> diff --git a/include/block/block.h b/include/block/block.h
> index 9b9d87b..13022d5 100644
> --- a/include/block/block.h
> +++ b/include/block/block.h
> @@ -428,7 +428,7 @@ int64_t bdrv_get_block_status_above(BlockDriverState *bs,
>  int bdrv_is_allocated(BlockDriverState *bs, int64_t offset, int64_t bytes,
>                        int64_t *pnum);
>  int bdrv_is_allocated_above(BlockDriverState *top, BlockDriverState *base,
> -                            int64_t sector_num, int nb_sectors, int *pnum);
> +                            int64_t offset, int64_t bytes, int64_t *pnum);
> 
>  bool bdrv_is_read_only(BlockDriverState *bs);
>  bool bdrv_is_writable(BlockDriverState *bs);
> diff --git a/block/commit.c b/block/commit.c
> index 241aa95..774a8a5 100644
> --- a/block/commit.c
> +++ b/block/commit.c
> @@ -146,7 +146,7 @@ static void coroutine_fn commit_run(void *opaque)
>      int64_t offset;
>      uint64_t delay_ns = 0;
>      int ret = 0;
> -    int n = 0; /* sectors */
> +    int64_t n = 0; /* bytes */
>      void *buf = NULL;
>      int bytes_written = 0;
>      int64_t base_len;
> @@ -171,7 +171,7 @@ static void coroutine_fn commit_run(void *opaque)
> 
>      buf = blk_blockalign(s->top, COMMIT_BUFFER_SIZE);
> 
> -    for (offset = 0; offset < s->common.len; offset += n * BDRV_SECTOR_SIZE) {
> +    for (offset = 0; offset < s->common.len; offset += n) {
>          bool copy;
> 
>          /* Note that even when no rate limit is applied we need to yield
> @@ -183,15 +183,12 @@ static void coroutine_fn commit_run(void *opaque)
>          }
>          /* Copy if allocated above the base */
>          ret = bdrv_is_allocated_above(blk_bs(s->top), blk_bs(s->base),
> -                                      offset / BDRV_SECTOR_SIZE,
> -                                      COMMIT_BUFFER_SIZE / BDRV_SECTOR_SIZE,
> -                                      &n);
> +                                      offset, COMMIT_BUFFER_SIZE, &n);
>          copy = (ret == 1);
> -        trace_commit_one_iteration(s, offset, n * BDRV_SECTOR_SIZE, ret);
> +        trace_commit_one_iteration(s, offset, n, ret);
>          if (copy) {
> -            ret = commit_populate(s->top, s->base, offset,
> -                                  n * BDRV_SECTOR_SIZE, buf);
> -            bytes_written += n * BDRV_SECTOR_SIZE;
> +            ret = commit_populate(s->top, s->base, offset, n, buf);
> +            bytes_written += n;
>          }
>          if (ret < 0) {
>              BlockErrorAction action =
> @@ -204,11 +201,10 @@ static void coroutine_fn commit_run(void *opaque)
>              }
>          }
>          /* Publish progress */
> -        s->common.offset += n * BDRV_SECTOR_SIZE;
> +        s->common.offset += n;
> 
>          if (copy && s->common.speed) {
> -            delay_ns = ratelimit_calculate_delay(&s->limit,
> -                                                 n * BDRV_SECTOR_SIZE);
> +            delay_ns = ratelimit_calculate_delay(&s->limit, n);
>          }
>      }
> 
> diff --git a/block/io.c b/block/io.c
> index 5bbf153..061a162 100644
> --- a/block/io.c
> +++ b/block/io.c
> @@ -1903,54 +1903,52 @@ int coroutine_fn bdrv_is_allocated(BlockDriverState *bs, int64_t offset,
>  /*
>   * Given an image chain: ... -> [BASE] -> [INTER1] -> [INTER2] -> [TOP]
>   *
> - * Return true if the given sector is allocated in any image between
> - * BASE and TOP (inclusive).  BASE can be NULL to check if the given
> - * sector is allocated in any image of the chain.  Return false otherwise,
> + * Return true if the (prefix of the) given range is allocated in any image
> + * between BASE and TOP (inclusive).  BASE can be NULL to check if the given
> + * offset is allocated in any image of the chain.  Return false otherwise,
>   * or negative errno on failure.
>   *
> - * 'pnum' is set to the number of sectors (including and immediately following
> - *  the specified sector) that are known to be in the same
> - *  allocated/unallocated state.
> + * 'pnum' is set to the number of bytes (including and immediately
> + * following the specified offset) that are known to be in the same
> + * allocated/unallocated state.  Note that a subsequent call starting
> + * at 'offset + *pnum' may return the same allocation status (in other
> + * words, the result is not necessarily the maximum possible range);
> + * but 'pnum' will only be 0 when end of file is reached.
>   *
>   */
>  int bdrv_is_allocated_above(BlockDriverState *top,
>                              BlockDriverState *base,
> -                            int64_t sector_num,
> -                            int nb_sectors, int *pnum)
> +                            int64_t offset, int64_t bytes, int64_t *pnum)
>  {
>      BlockDriverState *intermediate;
> -    int ret, n = nb_sectors;
> +    int ret;
> +    int64_t n = bytes;
> 
>      intermediate = top;
>      while (intermediate && intermediate != base) {
>          int64_t pnum_inter;
>          int64_t size_inter;
> -        int psectors_inter;
> 
> -        ret = bdrv_is_allocated(intermediate, sector_num * BDRV_SECTOR_SIZE,
> -                                nb_sectors * BDRV_SECTOR_SIZE,
> -                                &pnum_inter);
> +        ret = bdrv_is_allocated(intermediate, offset, bytes, &pnum_inter);
>          if (ret < 0) {
>              return ret;
>          }
> -        assert(pnum_inter < INT_MAX * BDRV_SECTOR_SIZE);
> -        psectors_inter = pnum_inter >> BDRV_SECTOR_BITS;
>          if (ret) {
> -            *pnum = psectors_inter;
> +            *pnum = pnum_inter;
>              return 1;
>          }
> 
>          /*
> -         * [sector_num, nb_sectors] is unallocated on top but intermediate
> -         * might have [sector_num+x, nb_sectors-x] allocated.
> +         * [offset, bytes] is unallocated on top but intermediate
> +         * might have [offset+x, bytes-x] allocated.
>           */
> -        size_inter = bdrv_nb_sectors(intermediate);
> +        size_inter = bdrv_getlength(intermediate);
>          if (size_inter < 0) {
>              return size_inter;
>          }
> -        if (n > psectors_inter &&
> -            (intermediate == top || sector_num + psectors_inter < size_inter)) {
> -            n = psectors_inter;
> +        if (n > pnum_inter &&
> +            (intermediate == top || offset + pnum_inter < size_inter)) {
> +            n = pnum_inter;
>          }
> 
>          intermediate = backing_bs(intermediate);
> diff --git a/block/mirror.c b/block/mirror.c
> index 0eb2af4..8c3752b 100644
> --- a/block/mirror.c
> +++ b/block/mirror.c
> @@ -621,6 +621,7 @@ static int coroutine_fn mirror_dirty_init(MirrorBlockJob *s)
>      BlockDriverState *bs = s->source;
>      BlockDriverState *target_bs = blk_bs(s->target);
>      int ret, n;
> +    int64_t count;
> 
>      end = s->bdev_length / BDRV_SECTOR_SIZE;
> 
> @@ -670,11 +671,13 @@ static int coroutine_fn mirror_dirty_init(MirrorBlockJob *s)
>              return 0;
>          }
> 
> -        ret = bdrv_is_allocated_above(bs, base, sector_num, nb_sectors, &n);
> +        ret = bdrv_is_allocated_above(bs, base, sector_num * BDRV_SECTOR_SIZE,
> +                                      nb_sectors * BDRV_SECTOR_SIZE, &count);
>          if (ret < 0) {
>              return ret;
>          }
> 
> +        n = DIV_ROUND_UP(count, BDRV_SECTOR_SIZE);
>          assert(n > 0);
>          if (ret == 1) {
>              bdrv_set_dirty_bitmap(s->dirty_bitmap, sector_num, n);
> diff --git a/block/replication.c b/block/replication.c
> index 8f3aba7..bf4462c 100644
> --- a/block/replication.c
> +++ b/block/replication.c
> @@ -264,7 +264,8 @@ static coroutine_fn int replication_co_writev(BlockDriverState *bs,
>      BdrvChild *top = bs->file;
>      BdrvChild *base = s->secondary_disk;
>      BdrvChild *target;
> -    int ret, n;
> +    int ret;
> +    int64_t n;
> 
>      ret = replication_get_io_status(s);
>      if (ret < 0) {
> @@ -283,14 +284,20 @@ static coroutine_fn int replication_co_writev(BlockDriverState *bs,
>       */
>      qemu_iovec_init(&hd_qiov, qiov->niov);
>      while (remaining_sectors > 0) {
> -        ret = bdrv_is_allocated_above(top->bs, base->bs, sector_num,
> -                                      remaining_sectors, &n);
> +        int64_t count;
> +
> +        ret = bdrv_is_allocated_above(top->bs, base->bs,
> +                                      sector_num * BDRV_SECTOR_SIZE,
> +                                      remaining_sectors * BDRV_SECTOR_SIZE,
> +                                      &count);
>          if (ret < 0) {
>              goto out1;
>          }
> 
> +        assert(QEMU_IS_ALIGNED(count, BDRV_SECTOR_SIZE));
> +        n = count >> BDRV_SECTOR_BITS;
>          qemu_iovec_reset(&hd_qiov);
> -        qemu_iovec_concat(&hd_qiov, qiov, bytes_done, n * BDRV_SECTOR_SIZE);
> +        qemu_iovec_concat(&hd_qiov, qiov, bytes_done, count);
> 
>          target = ret ? top : base;
>          ret = bdrv_co_writev(target, sector_num, n, &hd_qiov);
> @@ -300,7 +307,7 @@ static coroutine_fn int replication_co_writev(BlockDriverState *bs,
> 
>          remaining_sectors -= n;
>          sector_num += n;
> -        bytes_done += n * BDRV_SECTOR_SIZE;
> +        bytes_done += count;
>      }
> 
>  out1:
> diff --git a/block/stream.c b/block/stream.c
> index 0a56c29..eb18557 100644
> --- a/block/stream.c
> +++ b/block/stream.c
> @@ -112,7 +112,7 @@ static void coroutine_fn stream_run(void *opaque)
>      uint64_t delay_ns = 0;
>      int error = 0;
>      int ret = 0;
> -    int n = 0; /* sectors */
> +    int64_t n = 0; /* bytes */
>      void *buf;
> 
>      if (!bs->backing) {
> @@ -136,9 +136,8 @@ static void coroutine_fn stream_run(void *opaque)
>          bdrv_enable_copy_on_read(bs);
>      }
> 
> -    for ( ; offset < s->common.len; offset += n * BDRV_SECTOR_SIZE) {
> +    for ( ; offset < s->common.len; offset += n) {
>          bool copy;
> -        int64_t count = 0;
> 
>          /* Note that even when no rate limit is applied we need to yield
>           * with no pending I/O here so that bdrv_drain_all() returns.
> @@ -150,26 +149,25 @@ static void coroutine_fn stream_run(void *opaque)
> 
>          copy = false;
> 
> -        ret = bdrv_is_allocated(bs, offset, STREAM_BUFFER_SIZE, &count);
> -        n = DIV_ROUND_UP(count, BDRV_SECTOR_SIZE);
> +        ret = bdrv_is_allocated(bs, offset, STREAM_BUFFER_SIZE, &n);
>          if (ret == 1) {
>              /* Allocated in the top, no need to copy.  */
>          } else if (ret >= 0) {
>              /* Copy if allocated in the intermediate images.  Limit to the
>               * known-unallocated area [offset, offset+n*BDRV_SECTOR_SIZE).  */
>              ret = bdrv_is_allocated_above(backing_bs(bs), base,
> -                                          offset / BDRV_SECTOR_SIZE, n, &n);
> +                                          offset, n, &n);
> 
>              /* Finish early if end of backing file has been reached */
>              if (ret == 0 && n == 0) {
> -                n = (s->common.len - offset) / BDRV_SECTOR_SIZE;
> +                n = s->common.len - offset;
>              }
> 
>              copy = (ret == 1);
>          }
> -        trace_stream_one_iteration(s, offset, n * BDRV_SECTOR_SIZE, ret);
> +        trace_stream_one_iteration(s, offset, n, ret);
>          if (copy) {
> -            ret = stream_populate(blk, offset, n * BDRV_SECTOR_SIZE, buf);
> +            ret = stream_populate(blk, offset, n, buf);
>          }
>          if (ret < 0) {
>              BlockErrorAction action =
> @@ -188,10 +186,9 @@ static void coroutine_fn stream_run(void *opaque)
>          ret = 0;
> 
>          /* Publish progress */
> -        s->common.offset += n * BDRV_SECTOR_SIZE;
> +        s->common.offset += n;
>          if (copy && s->common.speed) {
> -            delay_ns = ratelimit_calculate_delay(&s->limit,
> -                                                 n * BDRV_SECTOR_SIZE);
> +            delay_ns = ratelimit_calculate_delay(&s->limit, n);
>          }
>      }
> 
> diff --git a/qemu-img.c b/qemu-img.c
> index c5709bf..ca984e1 100644
> --- a/qemu-img.c
> +++ b/qemu-img.c
> @@ -1516,12 +1516,16 @@ static int img_compare(int argc, char **argv)
>          }
> 
>          for (;;) {
> +            int64_t count;
> +
>              nb_sectors = sectors_to_process(total_sectors_over, sector_num);
>              if (nb_sectors <= 0) {
>                  break;
>              }
> -            ret = bdrv_is_allocated_above(blk_bs(blk_over), NULL, sector_num,
> -                                          nb_sectors, &pnum);
> +            ret = bdrv_is_allocated_above(blk_bs(blk_over), NULL,
> +                                          sector_num * BDRV_SECTOR_SIZE,
> +                                          nb_sectors * BDRV_SECTOR_SIZE,
> +                                          &count);
>              if (ret < 0) {
>                  ret = 3;
>                  error_report("Sector allocation test failed for %s",
> @@ -1529,7 +1533,7 @@ static int img_compare(int argc, char **argv)
>                  goto out;
> 
>              }
> -            nb_sectors = pnum;
> +            nb_sectors = DIV_ROUND_UP(count, BDRV_SECTOR_SIZE);
>              if (ret) {
>                  ret = check_empty_sectors(blk_over, sector_num, nb_sectors,
>                                            filename_over, buf1, quiet);
> -- 
> 2.9.4
>