Re: [Qemu-devel] [Fwd: [PATCH v4 07/21] iscsi: Handle failure for potentially large allocations]

[Peter Lieven <pl@kamp.de>]

Am 22.08.2014 um 09:35 schrieb Peter Lieven:
> Some code in the block layer makes potentially huge allocations. Failure
> is not completely unexpected there, so avoid aborting qemu and handle
> out-of-memory situations gracefully.
>
> This patch addresses the allocations in the iscsi block driver.
>
> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> Acked-by: Paolo Bonzini <pbonzini@redhat.com>
> Reviewed-by: Benoit Canet <benoit@irqsave.net>
> Reviewed-by: Eric Blake <eblake@redhat.com>
> ---
>  block/iscsi.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/block/iscsi.c b/block/iscsi.c
> index 84aa22a..06afa78 100644
> --- a/block/iscsi.c
> +++ b/block/iscsi.c
> @@ -893,7 +893,10 @@ coroutine_fn iscsi_co_write_zeroes(BlockDriverState
> *bs, int64_t sector_num,
>      nb_blocks = sector_qemu2lun(nb_sectors, iscsilun);
>
>      if (iscsilun->zeroblock == NULL) {
> -        iscsilun->zeroblock = g_malloc0(iscsilun->block_size);
> +        iscsilun->zeroblock = g_try_malloc0(iscsilun->block_size);
> +        if (iscsilun->zeroblock == NULL) {
> +            return -ENOMEM;
> +        }
>      }
>
>      iscsi_co_init_iscsitask(iscsilun, &iTask);

Unfortunately, I missed that one. The zeroblock is typicalls 512 Byte or 4K depending
on the blocksize. What is significantly larger is the allocationmap. It is typically created
on iscsi_open, but is also recreated on iscsi_truncate. I don't have the context why this
patch was introduced, but I would vote for introducing a bitmap_try_new and issue
a warning if the allocation fails. The allocationmap is optional we can work without it.
If the pointer is NULL its not used.

Peter