[Qemu-devel] Re: [PATCH 1/4] Add a scatter-gather list type and accessors

[Anthony Liguori <aliguori@us.ibm.com>]

Avi Kivity wrote:
> Anthony Liguori wrote:
>> Avi Kivity wrote:
>>> Scatter-gather lists are used extensively in dma-capable devices; a
>>> single data structure allows more code reuse later on.
>>>
>>> diff --git a/dma-helpers.c b/dma-helpers.c
>>> new file mode 100644
>>> index 0000000..315834e
>>> --- /dev/null
>>> +++ b/dma-helpers.c
>>> @@ -0,0 +1,29 @@
>>>   
>>
>> Needs copyright/license.
>
> Sure.
>
> Is it possible to have a blanket license for files which don't have 
> explicit terms?  I don't much like boilerplate.

I'd greatly prefer not to.  You can refer to a COPYING and we can have a 
default COPYING file but a copyright is really needed as far as I 
understand it.

>>
>>> +#include "dma.h"
>>> +
>>> +
>>> +void qemu_sglist_init(QEMUSGList *qsg, int alloc_hint)
>>> +{
>>> +    qsg->sg = qemu_malloc(alloc_hint * sizeof(ScatterGatherEntry));
>>>   
>>
>> Would be nice to check for malloc failures and fail gracefully at least.
>
> Do you mean an exit(1)?  If so we could just put it in qemu_malloc().

In theory, some users may be able to cope with malloc failure.  In 
practice, I don't think anyone can.  I'm open to suggestion.

> I expect this to trigger rarely since the allocation hint should 
> suffice nearly 100% of the time.  But in case we miss, it's better to 
> reallocate as little as possible.
>
> (what I really want is std::vector<>)

Which I'm pretty sure has a linear growth strategy :-)

Regards,

Anthony Liguori