forked from pool/rtl-sdr
52 lines
1.9 KiB
Diff
52 lines
1.9 KiB
Diff
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From f68bb2fa772ad94f58c59babd78353667570630b Mon Sep 17 00:00:00 2001
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From: Steve Markgraf <steve@steve-m.de>
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Date: Sun, 7 Oct 2018 01:16:07 +0200
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Subject: [PATCH] lib: Add workaround for Linux usbfs mmap() bug
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The Linux Kernel has a bug on ARM/ARM64 systems where the USB CMA
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memory is incorrectly mapped to userspace, breaking zerocopy.
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When the Kernel allocates the memory, it clears it with memset().
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If the mapping worked correctly, we should have zeroed out buffers,
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if it doesn't, we get random Kernel memory. We now check for this,
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and fall back to buffers in userspace if that's the case.
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Signed-off-by: Steve Markgraf <steve@steve-m.de>
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---
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src/librtlsdr.c | 19 +++++++++++++++++--
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1 file changed, 17 insertions(+), 2 deletions(-)
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diff --git a/src/librtlsdr.c b/src/librtlsdr.c
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index 433ed5b..89ec903 100644
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--- a/src/librtlsdr.c
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+++ b/src/librtlsdr.c
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@@ -1755,11 +1755,26 @@ static int _rtlsdr_alloc_async_buffers(rtlsdr_dev_t *dev)
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for (i = 0; i < dev->xfer_buf_num; ++i) {
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dev->xfer_buf[i] = libusb_dev_mem_alloc(dev->devh, dev->xfer_buf_len);
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- if (!dev->xfer_buf[i]) {
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+ if (dev->xfer_buf[i]) {
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+ /* Check if Kernel usbfs mmap() bug is present: if the
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+ * mapping is correct, the buffers point to memory that
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+ * was memset to 0 by the Kernel, otherwise, they point
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+ * to random memory. We check if the buffers are zeroed
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+ * and otherwise fall back to buffers in userspace.
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+ */
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+ if (dev->xfer_buf[i][0] || memcmp(dev->xfer_buf[i],
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+ dev->xfer_buf[i] + 1,
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+ dev->xfer_buf_len - 1)) {
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+ fprintf(stderr, "Detected Kernel usbfs mmap() "
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+ "bug, falling back to buffers "
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+ "in userspace\n");
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+ dev->use_zerocopy = 0;
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+ break;
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+ }
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+ } else {
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fprintf(stderr, "Failed to allocate zero-copy "
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"buffer for transfer %d\nFalling "
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"back to buffers in userspace\n", i);
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-
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dev->use_zerocopy = 0;
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break;
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}
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