[libvirt] [PATCH 1/6] storage_backend_iscsi_direct: Simplify vol zeroing

[Michal Privoznik]

On 3/1/19 11:42 AM, Michal Privoznik wrote:
> So far we have two branches: either we zero BLOCK_PER_PACKET
> (currently 128) block at one, or if we're close to the last block
> then we zero out one block at the time. This is very suboptimal.
> We know how many block are there left. Might as well just write
> them all at once.
> 
> Signed-off-by: Michal Privoznik <mprivozn at redhat.com>
> ---
>   src/storage/storage_backend_iscsi_direct.c | 20 +++++++-------------
>   1 file changed, 7 insertions(+), 13 deletions(-)
> 
> diff --git a/src/storage/storage_backend_iscsi_direct.c b/src/storage/storage_backend_iscsi_direct.c
> index 786663534d..574a65449d 100644
> --- a/src/storage/storage_backend_iscsi_direct.c
> +++ b/src/storage/storage_backend_iscsi_direct.c
> @@ -645,21 +645,15 @@ virStorageBackendISCSIDirectVolWipeZero(virStorageVolDefPtr vol,
>           return ret;
>   
>       while (lba < nb_block) {
> -        if (nb_block - lba > block_size * BLOCK_PER_PACKET) {
> +        const uint64_t to_write = MIN(nb_block - lba + 1, BLOCK_PER_PACKET);
>   
> -            if (!(task = iscsi_write16_sync(iscsi, lun, lba, data,
> -                                            block_size * BLOCK_PER_PACKET,
> -                                            block_size, 0, 0, 0, 0, 0)))
> -                return -1;
> -            scsi_free_scsi_task(task);
> -            lba += BLOCK_PER_PACKET;
> -        } else {
> -            if (!(task = iscsi_write16_sync(iscsi, lun, lba, data, block_size,
> +        if (!(task = iscsi_write16_sync(iscsi, lun, lba, data,
> +                                        to_write * block_size,
>                                           block_size, 0, 0, 0, 0, 0)))
> -                return -1;

Self-NACK. I've experimented a bit and realized we can use 
writesame16_sync() which allows us to allocate smaller buffer and also 
it is a bit faster. I'll post v2 for this one.

Michal