Re: [PATCH 2/6] block/vdi: Don't assume that blocks are larger than VdiHeader

[Max Reitz]

On 17.03.21 19:00, Paolo Bonzini wrote:
> From: David Edmondson <david.edmondson@oracle.com>
>
> Given that the block size is read from the header of the VDI file, a
> wide variety of sizes might be seen. Rather than re-using a block
> sized memory region when writing the VDI header, allocate an
> appropriately sized buffer.
>
> Signed-off-by: David Edmondson <david.edmondson@oracle.com>
> Message-Id: <20210309144015.557477-3-david.edmondson@oracle.com>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>   block/vdi.c | 10 ++++++----
>   1 file changed, 6 insertions(+), 4 deletions(-)
>
> diff --git a/block/vdi.c b/block/vdi.c
> index 2a6dc26124..548f8a057b 100644
> --- a/block/vdi.c
> +++ b/block/vdi.c
> @@ -696,18 +696,20 @@ nonallocating_write:
>   
>       if (block) {
>           /* One or more new blocks were allocated. */
> -        VdiHeader *header = (VdiHeader *) block;
> +        VdiHeader *header;
>           uint8_t *base;
>           uint64_t offset;
>           uint32_t n_sectors;
>   
> +        g_free(block);

This logic (checking @block != NULL) was a bit weird before and this 
just seems to accomodate it.  We probably shouldn’t check @block, but 
some boolean, and *block should be freed after the while () loop.

Considering the “if (block)” was there already and it’d be weird to keep 
that check if *block were freed by that point, I suppose this isn’t 
making it worse, though, so:

Reviewed-by: Max Reitz <mreitz@redhat.com>

> +        header = g_malloc(sizeof(*header));
> +
>           logout("now writing modified header\n");
>           assert(VDI_IS_ALLOCATED(bmap_first));
>           *header = s->header;
>           vdi_header_to_le(header);
> -        ret = bdrv_pwrite(bs->file, 0, block, sizeof(VdiHeader));
> -        g_free(block);
> -        block = NULL;
> +        ret = bdrv_pwrite(bs->file, 0, header, sizeof(*header));
> +        g_free(header);
>   
>           if (ret < 0) {
>               return ret;