On Wed, Jul 29, 2026 at 03:47:23PM +0530, Anuj Gupta/Anuj Gupta wrote: > > But I also don't understand what the use case for this function > > is to start with. struct sg_table tells us how many segments > > exist on the DMA side in the nents member, which should be just > > fine for the SGL threshold calculation. > > sg_table->nents covers the entire exported buffer (<=1GiB), while a > request only covers a subrange[bi_offset, bi_offset+payload). Using > nents would overcount the request's segments.
Urgg, yes. > >> + if (!entries) > >> + return BLK_STS_IOERR; > >> + if (entries > NVME_MAX_SEGS) > >> + return BLK_STS_AGAIN; > > > > Given that the block layer enforced data in rw/command and the > > max_segments limit, why do we need the extra check here? > > A dmabuf bio reports nsegs=1 (bio_split_io_at) to the block layer, so > max_segments isn't enforced against the SG entries actually spanned by > the request. Hence the explicit check. We'll need to expose the actual nsegs to the block layer and split based on that. Otherwise I/O might work or fail based on the device capabilities.
