Re: [Qemu-devel] [PATCH v5 RESEND 4/4] qcow2: Add full image preallocation option

[Hu Tao]

On Tue, Feb 11, 2014 at 03:07:10PM +0800, Hu Tao wrote:
> This adds a preallocation=full mode to qcow2 image creation, which
> creates a non-sparse image file.

Ping.

This is the major part of the patchset that needs review, especially 
the calculation of metadata size.

> 
> Signed-off-by: Hu Tao <address@hidden>
> ---
>  block/qcow2.c | 75 
> ++++++++++++++++++++++++++++++++++++++++++++++++++++++++---
>  1 file changed, 72 insertions(+), 3 deletions(-)
> 
> diff --git a/block/qcow2.c b/block/qcow2.c
> index e4bab70..4b113b7 100644
> --- a/block/qcow2.c
> +++ b/block/qcow2.c
> @@ -1456,6 +1456,7 @@ static int qcow2_create2(const char *filename, int64_t 
> total_size,
>                           QEMUOptionParameter *options, int version,
>                           Error **errp)
>  {
> +    QEMUOptionParameter *alloc_options = NULL;
>      /* Calculate cluster_bits */
>      int cluster_bits;
>      cluster_bits = ffs(cluster_size) - 1;
> @@ -1485,16 +1486,80 @@ static int qcow2_create2(const char *filename, 
> int64_t total_size,
>      Error *local_err = NULL;
>      int ret;
>  
> +    if (prealloc == PREALLOC_MODE_FULL) {
> +        int64_t meta_size = 0;
> +        unsigned nreftablee, nrefblocke, nl1e, nl2e;
> +        BlockDriver *drv;
> +
> +        total_size = align_offset(total_size, cluster_size);
> +
> +        drv = bdrv_find_protocol(filename, true);
> +        if (drv == NULL) {
> +            error_setg(errp, "Could not find protocol for file '%s'", 
> filename);
> +            return -ENOENT;
> +        }
> +
> +        alloc_options = append_option_parameters(alloc_options,
> +                                                 drv->create_options);
> +        alloc_options = append_option_parameters(alloc_options, options);
> +
> +        /* header: 1 cluster */
> +        meta_size += cluster_size;
> +
> +        /* total size of L2 tables */
> +        nl2e = total_size / cluster_size;
> +        nl2e = align_offset(nl2e, cluster_size / sizeof(uint64_t));
> +        meta_size += nl2e * sizeof(uint64_t);
> +
> +        /* total size of L1 tables */
> +        nl1e = nl2e * sizeof(uint64_t) / cluster_size;
> +        nl1e = align_offset(nl1e, cluster_size / sizeof(uint64_t));

Although not stated in the qcow2 spec, but actually l1 tables are
aligned to cluster too because of the nature of qcow2_alloc_clusters().

Same for refcount tables below.

> +        meta_size += nl1e * sizeof(uint64_t);
> +
> +        /* total size of refcount blocks
> +         *
> +         * note: every host cluster is reference-counted, including metadata
> +         * (even refcount blocks are recursively included).
> +         * Let:
> +         *   a = total_size (this is the guest disk size)
> +         *   m = meta size not including refcount blocks and refcount tables
> +         *   c = cluster size
> +         *   y1 = number of refcount blocks entries
> +         *   y2 = meta size including everything
> +         * then,
> +         *   y1 = (y2 + a)/c
> +         *   y2 = y1 * sizeof(u16) + y1 * sizeof(u16) * sizeof(u64) / c + m
> +         * we can get y1:
> +         *   y1 = (a + m) / (c - sizeof(u16) - sizeof(u16) * sizeof(u64) / c)
> +         */
> +        nrefblocke = (total_size + meta_size + cluster_size) /
> +            (cluster_size - sizeof(uint16_t) -
> +             1.0 * sizeof(uint16_t) * sizeof(uint64_t) / cluster_size);
> +        nrefblocke = align_offset(nrefblocke, cluster_size / 
> sizeof(uint16_t));
> +        meta_size += nrefblocke * sizeof(uint16_t);
> +
> +        /* total size of refcount tables */
> +        nreftablee = nrefblocke * sizeof(uint16_t) / cluster_size;
> +        nreftablee = align_offset(nreftablee, cluster_size / 
> sizeof(uint64_t));
> +        meta_size += nreftablee * sizeof(uint64_t);
> +
> +        set_option_parameter_int(alloc_options, BLOCK_OPT_SIZE,
> +                                 total_size + meta_size);
> +        set_option_parameter(alloc_options, BLOCK_OPT_PREALLOC, "full");
> +
> +        options = alloc_options;
> +    }
> +
>      ret = bdrv_create_file(filename, options, &local_err);
>      if (ret < 0) {
>          error_propagate(errp, local_err);
> -        return ret;
> +        goto out_options;
>      }
>  
>      ret = bdrv_file_open(&bs, filename, NULL, NULL, BDRV_O_RDWR, &local_err);
>      if (ret < 0) {
>          error_propagate(errp, local_err);
> -        return ret;
> +        goto out_options;
>      }
>  
>      /* Write the header */
> @@ -1611,6 +1676,8 @@ static int qcow2_create2(const char *filename, int64_t 
> total_size,
>      ret = 0;
>  out:
>      bdrv_unref(bs);
> +out_options:
> +    free_option_parameters(alloc_options);
>      return ret;
>  }
>  
> @@ -1646,6 +1713,8 @@ static int qcow2_create(const char *filename, 
> QEMUOptionParameter *options,
>                  prealloc = PREALLOC_MODE_OFF;
>              } else if (!strcmp(options->value.s, "metadata")) {
>                  prealloc = PREALLOC_MODE_METADATA;
> +            } else if (!strcmp(options->value.s, "full")) {
> +                prealloc = PREALLOC_MODE_FULL;
>              } else {
>                  error_setg(errp, "Invalid preallocation mode: '%s'",
>                             options->value.s);
> @@ -2211,7 +2280,7 @@ static QEMUOptionParameter qcow2_create_options[] = {
>      {
>          .name = BLOCK_OPT_PREALLOC,
>          .type = OPT_STRING,
> -        .help = "Preallocation mode (allowed values: off, metadata)"
> +        .help = "Preallocation mode (allowed values: off, metadata, full)"
>      },
>      {
>          .name = BLOCK_OPT_LAZY_REFCOUNTS,
> -- 
> 1.8.0
>