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samp_start_io( ) is a subordinate driver routine that is called by the samp_biostart( ) and samp_ioctl( ) entry point routines to determine whether an I/O operation can be initiated for this device instance. Many processes can queue I/O operations against this device, but I/O should not be initiated for an instance that is not ACTIVE.
After issuing an
ASSERT( )
call to verify the priority level,
the code calls the
LOCK(D3)
function to lock the instance's idata structure
and then checks the cfg_state
(configuration state) member.
If cfg_state is SUSPENDED,
it blocks on the synchronization variable
which is signaled by the
CFG_RESUME or CFG_REMOVE subfunctions
to the
config(D2)
entry point routine.
Note that the
SV_WAIT_SIG(D3)
function is used because this is a long-term wait
and must be interruptable by signals.
The driver will keep waiting;
eventually the cfg_state should change
to either REMOVED or ACTIVE
and the code will take the appropriate action.
If cfg_state is set to REMOVED,
the I/O operation can not be initiated.
The driver unlocks the idata structure
then returns the EIO error.
If cfg_state is
neither SUSPENDED or REMOVED,
it must be ACTIVE,
so the driver increments the in_progress counter
and calls the
UNLOCK(D3)
function to unlock the idata structure;
control returns to the calling routine
to continue with the I/O request.