Ubuntu

Hi,

I need to override ioctl operation for a few USB drivers (sierra, option, cdc-acm) on Linux Ubuntu 2.6.34sb2 to support TIOCOUTQ command.

Unfortunately, none of the drivers I mentioned above support TIOCOUTQ because it seems unclear to know amount of data inside a modem.

Does Linux provide a way to control amount of data not sent by a modem?

The better question is, does the hardware?

Linux provides flow control for USB modems so all the packets reach destination without loss.
It means Linux knows when modem buffer is full. It would be good to know how Linux checks it.

That doesn't mean it knows anything more than that, or even that it's the same for everything. What the buffer is and how it's used would depend on the hardware. What the buffer is and how it's used would depend on the hardware. The details would be in the driver.

All the USB modem drivers I test (cdc-acm, option, sierra) send data to modems by using usb_submit_urb call.
When packet is supposed to be sent kernel calls write_bulk_out_callback method informing USB driver that packet (or URB) was processed.

Unfortunately calling write_bulk method by kernel doesn't really mean that data were sent because sometimes data don't reach destination even in 60 seconds. So the data seem to stuck somewhere inside USB modem.

The facts Linux provides flow control without packet loss and sendto call blocks itself if modem buffer is full mean Linux can check if modem buffer is full and I hope can check amount of data inside.
if there is no way to know exact amount of data inside modem may be there exist a way to check if modem is empty at least?

Of course they do. Data for USB modems gets sent over USB. The modem must have a way to inform the Linux kernel when to send data or when not to send data but this depends on the hardware. Not necessarily. For some hardware it might be the other way around -- the modem might tell Linux when the buffer is full or not full.

How it works depends on the hardware.

Looks like I'd have to ask modem manufacturers if their modems can return how much data are inside modem buffer....
usb_submit_urb puts data to HCD (Host Controller Driver). Does HCD put data to device directly, or it transfers data to the next level of Linux kernel?



Is there at least one modem that returns buffer size information?