zx_clock_read_mapped

Summary

Perform a basic read of a mapped clock's state. Behaves identically to a call to zx_clock_read(), however it operates on a mapped clock's state instead of a clock handle, and may offer performance benefits as it usually does not need to enter the Zircon kernel in order to perform the read. See mappable clocks for more details.

Declaration

#include <zircon/syscalls.h>

zx_status_t zx_clock_read_mapped(const void* clock_addr, zx_time_t* now);

Rights

No handle is needed in order to perform a successful read, therefore no specific handle rights are needed either. Instead, the user must provide the virtual address of a currently valid clock state mapping, established using zx_vmar_map_clock()

Description

Perform a basic read of the clock's mapped state, and return its current time in the now out parameter.

Return value

On success, returns ZX_OK along with the clock's current time in the now output parameter.

Errors

Any attempt to pass a virtual pointer for clock_addr which was:

Not the value returned by the original call to zx_clock_map().
A pointer to clock state which has been either partially, or completely, unmapped.

Will result in undefined behavior.