>> Hello all, >> >> I've been doing some work with a Linux kernel module that enables zero-copy I/O to block devices using a custom user/kernel interface. In porting this from an older Linux kernel to a more modern release, I ran into an issue when interacting with MD devices that I traced back to what I believe to be a problem in bio_map_user_iov. >> >> The problem and fix are described in the first attached patch. The second is a simple test module and user program which triggers the bug and validates the fix. >> >> Thanks, >> -m >> >> ps. This is my first attempt at pushing a patch upstream so please forgive any newbie mistakes. >> > > I think the real issue here is that bio_map_user is an interface that was > only intended to be used by bottom level devices like SCSI drivers etc. > It is a function that a device driver can use if it knows that it makes sense > to use it. > > You are trying to use it as a generic interface that works for all block > devices, and it wasn't intended for that. > > So while it is reasonably simple to 'fix' bio_map_user_iov, it is not > possible to 'fix' bio_map_kern_iov in the same way, because it doesn't have > access to the bdev at all. > > > So the question we should be asking is: are you really using the right > interface for the job? Is bio_map_user something that you really should be > using? > And to answer that, we would need to know what you are trying to do. > > And why isn't O_DIRECT a suitable zero-copy interface for I/O to block > devices? Thanks -- I understand your concerns, but unfortunately I can't really go into more detail about our use case since it's something we use internally. Given which, I understand your potential reluctance to take the patch. Best, -m -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
