Re: [Qemu-devel] [PATCH 18/19] block/parallels: add prealloc-mode and prealloc-size open paramemets

[Roman Kagan]

On Tue, Dec 30, 2014 at 01:07:11PM +0300, Denis V. Lunev wrote:
> This is preparational commit for tweaks in Parallels image expansion.
> The idea is that enlarge via truncate by one data block is slow. It
> would be much better to use fallocate via bdrv_write_zeroes and
> expand by some significant amount at once.
> 
> This patch just adds proper parameters into BDRVParallelsState and
> performs options parsing in parallels_open.
> 
> Signed-off-by: Denis V. Lunev <address@hidden>
> CC: Kevin Wolf <address@hidden>
> CC: Stefan Hajnoczi <address@hidden>
> ---
>  block/parallels.c | 72 
> +++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 72 insertions(+)
> 
> diff --git a/block/parallels.c b/block/parallels.c
> index 18b9267..12a9cea 100644
> --- a/block/parallels.c
> +++ b/block/parallels.c
> @@ -30,6 +30,7 @@
>  #include "qemu-common.h"
>  #include "block/block_int.h"
>  #include "qemu/module.h"
> +#include "qapi/util.h"
>  
>  /**************************************************************/
>  
> @@ -54,6 +55,20 @@ typedef struct ParallelsHeader {
>      char padding[12];
>  } QEMU_PACKED ParallelsHeader;
>  
> +
> +typedef enum ParallelsPreallocMode {
> +    PRL_PREALLOC_MODE_FALLOCATE = 0,
> +    PRL_PREALLOC_MODE_TRUNCATE = 1,
> +    PRL_PREALLOC_MODE_MAX = 2,
> +} ParallelsPreallocMode;
> +
> +static const char *prealloc_mode_lookup[] = {
> +    "falloc",
> +    "truncate",
> +    NULL,

There is already generic "preallocaton" option, BLOCK_OPT_PREALLOC,
which is handled by qcow2 and raw-posix.  It means slightly different
thing: the *whole* image is preallocated using the method specified.

I think it would make sense to consolidate that option with this new
batched allocation in the generic block code.  I guess qcow2 and
raw-posix would benefit from it, too.

At any rate I think it's a matter for a separate patchset.

Roman.