rw_iswriter

Checks whether a writer is holding or waiting for the specified reader-writer lock.

int rw_iswriter(vmlinux`rwlock_t *rwlock)

The rw_iswriter function returns non-zero if a writer is holding or waiting for the specified reader-writer lock (rwlock). If the lock is held only by readers and no writer is blocked, or if the lock isn't held at all, rw_iswriter returns zero.

Example 7-40 How to use rw_iswriter to check whether a writer is holding or waiting for a specified reader-writer lock

The example contains two clauses. The first clause triggers for when the _raw_write_lock is entered, and uses rw_iswriter function to print whether a lock is held. At this stage, no lock is held, so the output returns 0. When the _raw_write_lock returns, a lock is held and the rw_iswriter function returns 1 and exits.

fbt:vmlinux:_raw_write_lock:entry
{
         self->wlock = (rwlock_t *)arg0;
         printf("write entry  %x\n", 0 != rw_iswriter(self->wlock));
}
 
fbt:vmlinux:_raw_write_lock:return
/self->wlock/
{
         printf("write return %x\n", 0 != rw_iswriter(self->wlock));
         exit(0)
}