Man page 9 : usb_sg_init

usb_sg_init - initializes scatterlist-based bulk/interrupt I/O request

int usb_sg_init(struct usb_sg_request *  io , struct usb_device *  dev , unsigned  pipe , unsigned  period , struct scatterlist *  sg , int  nents , size_t  length , gfp_t  mem_flags );

io
    request block being initialized. until usb_sg_wait returns, treat this as a pointer to an opaque block of memory,

dev
    the usb device that will send or receive the data

pipe
    endpoint « pipe » used to transfer the data

period
    polling rate for interrupt endpoints, in frames or (for high speed endpoints) microframes; ignored for bulk

sg
    scatterlist entries

nents
    how many entries in the scatterlist

length
    how many bytes to send from the scatterlist, or zero to send every byte identified in the list.

mem_flags
    SLAB_* flags affecting memory allocations in this call

Returns zero for success, else a negative errno value. This initializes a scatter/gather request, allocating resources such as I/O mappings and urb memory (except maybe memory used by USB controller drivers).

The request must be issued using usb_sg_wait, which waits for the I/O to complete (or to be canceled) and then cleans up all resources allocated by usb_sg_init.

The request may be canceled with usb_sg_cancel, either before or after usb_sg_wait is called.