No. If the act of write() is to construct and transmit and SKB, and SKB can be created from a scatter/gather list of pages plus an offset into the first page.

No. If the act of write() is to construct and transmit and SKB, and SKB can be created from a scatter/gather list of pages plus an offset into the first page. But this implies that you can track the SKBs lifecycle in the kernel such that you can know when the SKB is done being used and therefore can allow write() to return. The trouble is, a write() to a socket doesn't actually generate an SKB. Instead it copies data to a socket buffer and then the socket buffers are used to generate SKBs. Some of this is meant as an optimization to create large packets even from small writes. But of course, a copy is a copy and sometimes this buffering is not actually helpful to userspace.