pcap streams are text files which insert 0xD in Windows version

[Benjamin David Lunt]

Since Windows text files use CRLFs for all \n, the Windows version of QEMU inserts a CR in the PCAP stream when a LF is encountered when using USB PCAP files.

Starting at line 275 in hw/usb/bus (https://gitlab.com/qemu-project/qemu/-/blob/master/hw/usb/bus.c?ref_type=heads#L275), the file is opened as text instead of binary.

I think the following patch would fix the issue:
    if (dev->pcap_filename) {
- int fd = qemu_open_old(dev->pcap_filename, O_CREAT | O_WRONLY | O_TRUNC, 0666);
+ int fd = qemu_open_old(dev->pcap_filename, O_CREAT | O_WRONLY | O_TRUNC | O_BINARY, 0666);
        if (fd < 0) {
            error_setg(errp, "open %s failed", dev->pcap_filename);
            usb_qdev_unrealize(qdev);
            return;
        }
- dev->pcap = fdopen(fd, "w");
+ dev->pcap = fdopen(fd, "wb");
        usb_pcap_init(dev->pcap);
    }

To show an example, when using a very common protocol to USB disks, the BBB protocol uses a 10-byte command packet. For example, the READ_CAPACITY(10) command (implemented at https://gitlab.com/qemu-project/qemu/-/blob/master/hw/scsi/scsi-disk.c#L2068) will have a command block length of 10 (0xA). When this 10-byte command (part of the 31-byte CBW) is placed into the PCAP file, the Windows file manager inserts a 0xD before the 0xA, turning the 31-byte CBW into a 32-byte CBW.

Actual CBW:
  0040 55 53 42 43 01 00 00 00 08 00 00 00 80 00 0a 25 USBC............
  0050 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 %..............

PCAP CBW
  0040 55 53 42 43 01 00 00 00 08 00 00 00 80 00 0d 0a USBC............
  0050 25 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 %..............

I believe simply opening the PCAP file as BINARY instead of TEXT will fix this issue.

Thank you.

[Philippe Mathieu-Daudé (philmd)]

Hi Benjamin,

QEMU bug tracker is on GitLab:
https://gitlab.com/qemu-project/qemu/-/issues

But instead of re-opening the issue there, since you
already figured the problem, do you mind directly post
your patch? See guidelines there:
https://www.qemu.org/docs/master/devel/submitting-a-patch.html

Thanks!

Phil.

[Benjamin David Lunt (fysnet)]

I have sent a patch as directed. I hope it is correctly done.

Thank you.
Ben