serenity/Kernel/API/TimePage.h

/*
 * Copyright (c) 2021, Andreas Kling <kling@serenityos.org>
 *
 * SPDX-License-Identifier: BSD-2-Clause
 */

#pragma once

#include <AK/Types.h>

#ifdef KERNEL
#    include <Kernel/UnixTypes.h>
#else
#    include <time.h>
#endif

namespace Kernel {

inline bool time_page_supports(clockid_t clock_id)
{
    return clock_id == CLOCK_REALTIME_COARSE || clock_id == CLOCK_MONOTONIC_COARSE;
}

struct TimePage {
    volatile u32 update1;
    struct timespec clocks[CLOCK_ID_COUNT];
    volatile u32 update2;
};

}
Kernel+LibC: Allow clock_gettime() to run without syscalls This patch adds a vDSO-like mechanism for exposing the current time as an array of per-clock-source timestamps. LibC's clock_gettime() calls sys$map_time_page() to map the kernel's "time page" into the process address space (at a random address, ofc.) This is only done on first call, and from then on the timestamps are fetched from the time page. This first patch only adds support for CLOCK_REALTIME, but eventually we should be able to support all clock sources this way and get rid of sys$clock_gettime() in the kernel entirely. :^) Accesses are synchronized using two atomic integers that are incremented at the start and finish of the kernel's time page update cycle. 2021-08-10 11:44:01 +00:00			`/*`
			`* Copyright (c) 2021, Andreas Kling <kling@serenityos.org>`
			`*`
			`* SPDX-License-Identifier: BSD-2-Clause`
			`*/`

			`#pragma once`

			`#include <AK/Types.h>`

			`#ifdef KERNEL`
			`# include <Kernel/UnixTypes.h>`
			`#else`
			`# include <time.h>`
			`#endif`

			`namespace Kernel {`

			`inline bool time_page_supports(clockid_t clock_id)`
			`{`
Kernel: Add CLOCK_MONOTONIC_COARSE to the kernel time page This allows clock_gettime(CLOCK_MONOTONIC_COARSE) without syscalls. Core::EventLoop takes advantage of this automatically. :^) 2021-08-10 19:31:31 +00:00			`return clock_id == CLOCK_REALTIME_COARSE \|\| clock_id == CLOCK_MONOTONIC_COARSE;`
Kernel+LibC: Allow clock_gettime() to run without syscalls This patch adds a vDSO-like mechanism for exposing the current time as an array of per-clock-source timestamps. LibC's clock_gettime() calls sys$map_time_page() to map the kernel's "time page" into the process address space (at a random address, ofc.) This is only done on first call, and from then on the timestamps are fetched from the time page. This first patch only adds support for CLOCK_REALTIME, but eventually we should be able to support all clock sources this way and get rid of sys$clock_gettime() in the kernel entirely. :^) Accesses are synchronized using two atomic integers that are incremented at the start and finish of the kernel's time page update cycle. 2021-08-10 11:44:01 +00:00			`}`

			`struct TimePage {`
			`volatile u32 update1;`
			`struct timespec clocks[CLOCK_ID_COUNT];`
			`volatile u32 update2;`
			`};`

			`}`