On Tue, 8 Dec 2015, Steinar H. Gunderson wrote: > On Tue, Dec 08, 2015 at 03:26:28PM -0500, Alan Stern wrote: > > I just noticed this -- usbm->memlist needs to be initialized before > > dec_usb_memory_use_count() can be called. INIT_LIST_HEAD before the > > "if" statement will fix the problem. > > Done. > > > The patch could use one more ingredient. In > > include/uapi/linux/usbdevicefs_h, add a #define for USBDEVFS_CAP_MMAP > > and fix up proc_get_capabilities() to report the new capability. In > > theory, user programs could just try an mmap() call and see if it > > works, but this seems cleaner. > > Done. > > /* Steinar */ > > From 03318604cc6ad9def451784da407e6fcd6af4705 Mon Sep 17 00:00:00 2001 > From: "Steinar H. Gunderson" <sesse@xxxxxxxxxx> > Date: Thu, 26 Nov 2015 01:19:13 +0100 > Subject: [PATCH] Add support for usbfs zerocopy. > > Add a new interface for userspace to preallocate memory that can be > used with usbfs. This gives two primary benefits: > > - Zerocopy; data no longer needs to be copied between the userspace > and the kernel, but can instead be read directly by the driver from > userspace's buffers. This works for all kinds of transfers (even if > nonsensical for control and interrupt transfers); isochronous also > no longer need to memset() the buffer to zero to avoid leaking kernel data. > > - Once the buffers are allocated, USB transfers can no longer fail due to > memory fragmentation; previously, long-running programs could run into > problems finding a large enough contiguous memory chunk, especially on > embedded systems or at high rates. > > Memory is allocated by using mmap() against the usbfs file descriptor, > and similarly deallocated by munmap(). Once memory has been allocated, > using it as pointers to a bulk or isochronous operation means you will > automatically get zerocopy behavior. Note that this also means you cannot > modify outgoing data until the transfer is complete. The same holds for > data on the same cache lines as incoming data; DMA modifying them at the > same time could lead to your changes being overwritten. > > There's a new capability USBDEVFS_CAP_MMAP that userspace can query to see > if the running kernel supports this functionality, if just trying mmap() is > not acceptable. > > Largely based on a patch by Markus Rechberger with some updates. The original > patch can be found at: > > http://sundtek.de/support/devio_mmap_v0.4.diff > > Signed-off-by: Steinar H. Gunderson <sesse@xxxxxxxxxx> > Signed-off-by: Markus Rechberger <mrechberger@xxxxxxxxx> I don't see anything else to change. You can submit this to Greg KH and add: Acked-by: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> Alan Stern -- 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
