Hey, On 2023-02-15 11:48, Paul Cercueil wrote:
Hi, I am working on adding support for DMABUFs in the IIO subsystem. One thing we want there, is the ability to specify the number of bytes to transfer (while still defaulting to the DMABUF size). Since dma_buf_map_attachment() returns a sg_table, I basically have two options, and I can't decide which one is the best (or the less ugly): - Either I add a new API function similar to dmaengine_prep_slave_sg(), which still takes a scatterlist as argument but also takes the number of bytes as argument; - Or I add a function to duplicate the scatterlist and then shrink it manually, which doesn't sound like a good idea either. What would be the recommended way?
Does this need an api change? If you create a DMA-BUF of size X, it has to be of size X. You can pad with a dummy page probably if you know it in advance. But after it has been imported, it cannot change size.
You don´t have to write the entire dma-buf either, so if you want to create a 1GB buf and only use the first 4K, that is allowed. The contents of the remainder of the DMA-BUF are undefined. It's up to userspace to assign a meaning to it.
I think I'm missing something here that makes the whole question m,ake more sense.
~Maarten
