On Mon, Oct 18, 2010 at 3:19 AM, Rajat Sharma <fs.rajat@xxxxxxxxx> wrote: > >> Doesn't that mean user space right to block device? Simply based on >> that, I can see you fail all these times... because you do it from >> kernel space..and that's against the very basic meaning of direct I/O > > You can visualize direct I/O for two purpose: > > 1. Zero copy directly from user buffers to block device as you pointed out. > 2. Don't make an extra effort to cache the data in page-cache, as it might > have already be done by applications. > > In some cases, you may not afford to solve 1., e.g. you may want to > manipulate data before writing it do target. Although this can be done on > the same user space buffer, but you may not want to do that because it may > change the working data set of application. > > Anyways, to cut it short again, I had put my requirements in my original > mail, and I have one solution where I map pages in user space, I am looking > for a better solution, or the verification that there is none, where I can > directly user kernel buffers for doing non-cached I/O. > > Rajat Rajat, I'm not specifically familiar with a use-case in the kernel where the data based in via directio call is copied to kernel buffers, manipulated, then passed on. Thus I seriously doubt your use-case is supported. Why do you want to do that in the first place? Greg -- To unsubscribe from this list: send an email with "unsubscribe kernelnewbies" to ecartis@xxxxxxxxxxxx Please read the FAQ at http://kernelnewbies.org/FAQ
