Re: [Qemu-devel] [PATCH v3 04/16] qemu-img: Expose PreallocMode for resizing

[Eric Blake]

On 05/26/2017 11:55 AM, Max Reitz wrote:
> Add a --preallocation command line option to qemu-img resize which can
> be used to set the PreallocMode parameter of blk_truncate().
> 
> Signed-off-by: Max Reitz <address@hidden>
> ---
>  qemu-img.c    | 33 ++++++++++++++++++++++++++++++---
>  qemu-img.texi |  7 ++++++-
>  2 files changed, 36 insertions(+), 4 deletions(-)

> @@ -3553,8 +3566,16 @@ static int img_resize(int argc, char **argv)
>          goto out;
>      }
>  
> +    current_size = blk_getlength(blk);
> +    if (current_size < 0) {
> +        error_report("Failed to inquire current image length: %s",
> +                     strerror(-current_size));
> +        ret = -1;
> +        goto out;
> +    }
> +
>      if (relative) {
> -        total_size = blk_getlength(blk) + n * relative;
> +        total_size = current_size + n * relative;

You snuck in a bug fix here (reporting failure, rather than using a
bogus total_size, if querying the size fails).  Please mention that in
the commit message.

> @@ -541,6 +541,11 @@ After using this command to grow a disk image, you must 
> use file system and
>  partitioning tools inside the VM to actually begin using the new space on the
>  device.
>  
> +When growing an image, the @code{--preallocation} option may be used to 
> specify
> +how the additional image area should be allocated on the host.  See the 
> format
> +description in the @code{NOTES} section which values are allowed.  Using this
> +option may result in more data being allocated than necessary.

Should we tone it down a bit by saying 'slightly more data'?  (We'd
rather over-estimate than fall short, but our over-estimation will
probably be < 1% off, and not something drastic like an order of
magnitude off).

With the improved commit message,
Reviewed-by: Eric Blake <address@hidden>

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org

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