On Mon, Feb 11, 2019 at 11:26:49AM -0700, Jason Gunthorpe wrote: > On Mon, Feb 11, 2019 at 10:19:22AM -0800, Ira Weiny wrote: > > What if user space then writes to the end of the file with a regular write? > > Does that write end up at the point they truncated to or off the end of the > > mmaped area (old length)? > > IIRC it depends how the user does the write.. > > pwrite() with a given offset will write to that offset, re-extending > the file if needed > > A file opened with O_APPEND and a write done with write() should > append to the new end > > A normal file with a normal write should write to the FD's current > seek pointer. > > I'm not sure what happens if you write via mmap/msync. > > RDMA is similar to pwrite() and mmap. A pertinent point that you didn't mention is that ftruncate() does not change the file offset. So there's no user-visible change in behaviour.
