Add to the usbmon documentation to clarify how much of the packet text-mode users can expect to see. This is useful if packet lengths are not what they were expected to be. Signed-off-by: Richard Ash <richard@xxxxxxxxxxxxxxxx> --- On Fri, Apr 15, 2011 at 3:17 PM, Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote: > On Fri, 15 Apr 2011, Richard Ash wrote: >> [...] >> Once it's got going, the usbmon trace looks like this: >> >> f5146880 554152969 C Bi:4:002:1 0 128 = e6232508 0020e72e 3afcf03a >> 03933424 250800b0 e72e3afc f03a030e 83242508 >> f5146880 554152997 S Bi:4:002:1 -115 128 < >> f5146500 554153005 C Bi:4:002:1 0 128 = 260800f0 e72e3afc f03a0326 >> cf4e2608 00d0e72e 3afcf03a 03a21d4f 260800e0 > > ... > >> This is where I get confused - my device is apparently being asked for >> 128 bytes of data, and replying with 128 bytes, but only 32 bytes end >> up in the output. This is for a 64 byte endpoint ... >> >> The last two replies (with reported lengths of 19 and 23 bytes) do >> have 19 and 23 bytes of output data respectively. >> >> Can anyone explain when a length in usbmon output is not a length, and >> separately why a device with 64byte max packet size is doing 128 byte >> reads? > > Read the Documentation/usb/usbmon.txt file. Briefly, usbmon's text > interface displays only the first 32 bytes of each transfer. If you > want to see the complete data for each transfer, you need to use the > binary interface. The easiest way to do that is to run Wireshark, > although Pete Zaitcev has written a command-line program to do the same > thing: > > http://people.redhat.com/zaitcev/linux/usbmon-5.4.tar.gz I did read that file, but because it didn't say how much of the data you might get, missed the existence of the limit (and anyway, was concerned that 64 / 2 = 32). diff -u usb-2.6-vanilla/Documentation/usb/usbmon.txt usb-2.6-patched/Documentation/usb/usbmon.txt --- usb-2.6-vanilla/Documentation/usb/usbmon.txt 2011-04-13 20:17:14.000000000 +0100 +++ usb-2.6-patched/Documentation/usb/usbmon.txt 2011-04-15 16:18:30.016288637 +0100 @@ -165,12 +165,12 @@ - Data words follow, in big endian hexadecimal format. Notice that they are not machine words, but really just a byte stream split into words to make it easier to read. Thus, the last word may contain from one to four bytes. - The length of collected data is limited and can be less than the data length - reported in the Data Length word. In the case of an Isochronous input (Zi) - completion where the received data is sparse in the buffer, the length of - the collected data can be greater than the Data Length value (because Data - Length counts only the bytes that were received whereas the Data words - contain the entire transfer buffer). + The length of collected data is limited to 32 bytes and can be less than + the data length reported in the Data Length word. + In the case of an Isochronous input (Zi) completion where the received data + is sparse in the buffer, the length of the collected data can be greater than + the Data Length value (because Data Length counts only the bytes that were + received whereas the Data words contain the entire transfer buffer). Examples: -- 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
