Upgrades a disabled read-write from read-shared to write exclusive mode.
| Item | Description |
|---|---|
| lock_addr | Specifies the address of the lock word to lock. |
The drw_lock_read_to_write and drw_lock_try_read_to_write kernel services try to upgrade the specified read-write lock from read-shared to write-exclusive mode. The caller must hold the lock in read mode. The lock is successfully upgraded if no other thread has already requested write-exclusive access for this lock. If the lock cannot be upgraded, it is no longer held on return from the drw_lock_read_to_write kernel service; it is still held in shared-read mode on return from the drw_lock_try_read_to_write kernel service.
The calling kernel thread must hold the lock in shared-read mode.
The drw_lock_read_to_write and drw_lock_try_read_to_write kernel services may be called from either the process environment or the interrupt environment. However, if called from the process environment, interrupts must be disabled to some interrupt priority other than INTBASE.
The following only apply to drw_lock_read_to_write:
| Item | Description |
|---|---|
| TRUE | Indicates that the lock was successfully upgraded to exclusive-write mode. |
| FALSE | Indicates that the lock was not upgraded to exclusive-write mode and the lock is no longer held by the caller. |
The following only apply to lock_try_read_to_write:
| Item | Description |
|---|---|
| TRUE | Indicates that the lock was successfully upgraded to exclusive-write mode. |
| FALSE | Indicates that the lock was not upgraded and is held in read mode. |