From: Christoph Hellwig > Sent: 08 January 2016 09:46 > On Wed, Jan 06, 2016 at 10:35:05AM -0500, Alan Stern wrote: > > Indeed, the I/O operations we are using with mmap here are not reads or > > writes; they are ioctls. As far as I know, the kernel doesn't have any > > defined interface for zerocopy ioctls. > > IF it was using mmap for I/O it would read in through the page fault > handler an then mark the page dirty for writeback by the VM. Thats > clearly not the case. Indeed, and never is the case when mmap() is processed by a driver rather than a filesystem. > Instead it's using mmap on a file as a pecial purpose anonymous > memory allocator, bypassing the VM and VM policies, including > allowing to pin kernel memory that way. Opening a driver often allocates kernel memory, not a big deal. David -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
