Re: usbmon packet data format

This is the structure being returned:

struct usbmon_packet {
        u64 id;                 /*  0: URB ID - from submission to callback */
        unsigned char type;     /*  8: Same as text; extensible. */
        unsigned char xfer_type; /*    ISO (0), Intr, Control, Bulk (3) */
        unsigned char epnum;    /*     Endpoint number and transfer direction */
        unsigned char devnum;   /*     Device address */
        u16 busnum;             /* 12: Bus number */
        char flag_setup;        /* 14: Same as text */
        char flag_data;         /* 15: Same as text; Binary zero is OK. */
        s64 ts_sec;             /* 16: gettimeofday */
        s32 ts_usec;            /* 24: gettimeofday */
        int status;             /* 28: */
        unsigned int length;    /* 32: Length of data (submitted or actual) */
        unsigned int len_cap;   /* 36: Delivered length */
        unsigned char setup[8]; /* 40: Only for Control 'S' */
};                              /* 48 bytes total */

I'm not too keen on using an ASCII 'S' in the setup field to tell
whether setup[8] is in use or not. Am I correct in thinking that
setup[8] is always active on an URB submission and never active on a
completion or error? If that is the case then the flag_setup field is
redundant with the type field and can be eliminated. I would then make
the setup[8] presence variable depending on the packet type.

I also think flag_data is redundant based on the packet type, but I'm
not sure yet.

status looks to be active only on an error completion so the field
could be a union with setup[8].

The protocol can be further compressed by not including these fields:
xfer_type,  epnum,  devnum,  busnum in completion/error packets. I
already have to track the URB submissions in order to decode the
protocol so I have these fields from the submission packet and they
can't change assuming that I'm understanding everything correctly.


-- 
Jon Smirl
[email protected]

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