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[WIP] [LibOS] Add support for timerfd system calls
This commit adds support for system calls that create and operate on a timer that delivers timer expiration notifications via a file descriptor, specifically: `timerfd_create()`, `timerfd_settime()` and `timerfd_gettime()`. The timerfd object is associated with a dummy eventfd created on the host to trigger notifications (e.g., in epoll). The object is created inside Gramine, with all it operations resolved entirely inside Gramine. The emulation is currently implemented at the level of a single process. However, it may sometimes work for multi-process applications, e.g., if the child process inherits the timerfd object but doesn't use it; to support these cases, we introduce the `sys.experimental__allow_timerfd_fork` manifest option. LibOS regression tests are also added. Signed-off-by: Kailun Qin <[email protected]>
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,17 @@ | ||
| /* SPDX-License-Identifier: LGPL-3.0-or-later */ | ||
| /* Copyright (C) 2024 Intel Corporation | ||
| * Kailun Qin <[email protected]> | ||
| */ | ||
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| #pragma once | ||
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| /* Types and structures used by various Linux ABIs (e.g. syscalls). */ | ||
| /* These need to be binary-identical with the ones used by Linux. */ | ||
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| #include <linux/timerfd.h> | ||
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| #define TFD_SHARED_FCNTL_FLAGS (TFD_CLOEXEC | TFD_NONBLOCK) | ||
| /* Flags for timerfd_create. */ | ||
| #define TFD_CREATE_FLAGS TFD_SHARED_FCNTL_FLAGS | ||
| /* Flags for timerfd_settime. */ | ||
| #define TFD_SETTIME_FLAGS (TFD_TIMER_ABSTIME | TFD_TIMER_CANCEL_ON_SET) |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,124 @@ | ||
| /* SPDX-License-Identifier: LGPL-3.0-or-later */ | ||
| /* Copyright (C) 2024 Intel Corporation | ||
| * Kailun Qin <[email protected]> | ||
| */ | ||
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| /* | ||
| * This file contains code for implementation of 'timerfd' filesystem. | ||
| */ | ||
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| #include "libos_fs.h" | ||
| #include "libos_handle.h" | ||
| #include "libos_internal.h" | ||
| #include "libos_lock.h" | ||
| #include "linux_abi/errors.h" | ||
| #include "pal.h" | ||
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| static void timerfd_dummy_host_read(struct libos_handle* hdl, uint64_t* out_host_val) { | ||
| uint64_t buf_dummy_host_val = 0; | ||
| size_t dummy_host_val_count = sizeof(buf_dummy_host_val); | ||
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| int ret = PalStreamRead(hdl->pal_handle, /*offset=*/0, &dummy_host_val_count, | ||
| &buf_dummy_host_val); | ||
| if (ret < 0 || dummy_host_val_count != sizeof(buf_dummy_host_val)) { | ||
| /* should not happen in benign case, but can happen under racing, e.g. threads may race on | ||
| * the same eventfd event, one of them wins and updates `dummy_host_val` and the other one | ||
| * looses and gets an unexpected `dummy_host_val` */ | ||
| log_warning("timerfd dummy host read failed or got unexpected value"); | ||
| return; | ||
| } | ||
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| if (out_host_val) | ||
| *out_host_val = buf_dummy_host_val; | ||
| } | ||
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| static ssize_t timerfd_read(struct libos_handle* hdl, void* buf, size_t count, file_off_t* pos) { | ||
| __UNUSED(pos); | ||
| assert(hdl->type == TYPE_TIMERFD); | ||
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| if (count < sizeof(uint64_t)) | ||
| return -EINVAL; | ||
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| int ret; | ||
| spinlock_lock(&hdl->info.timerfd.expiration_lock); | ||
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| while (!hdl->info.timerfd.num_expirations) { | ||
| if (hdl->flags & O_NONBLOCK) { | ||
| ret = -EAGAIN; | ||
| goto out; | ||
| } | ||
| /* must block -- use the host's blocking read() on a dummy eventfd */ | ||
| if (hdl->info.timerfd.dummy_host_val) { | ||
| /* value on host is non-zero, must perform a read to make it zero (and thus the next | ||
| * read will become blocking) */ | ||
| uint64_t host_val = 0; | ||
| timerfd_dummy_host_read(hdl, &host_val); | ||
| if (host_val != hdl->info.timerfd.dummy_host_val) | ||
| BUG(); | ||
| hdl->info.timerfd.dummy_host_val = 0; | ||
| } | ||
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| spinlock_unlock(&hdl->info.timerfd.expiration_lock); | ||
| /* blocking read to wait for some value (we don't care which value) */ | ||
| timerfd_dummy_host_read(hdl, /*out_host_val=*/NULL); | ||
| spinlock_lock(&hdl->info.timerfd.expiration_lock); | ||
| hdl->info.timerfd.dummy_host_val = 0; | ||
| } | ||
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| memcpy(buf, &hdl->info.timerfd.num_expirations, sizeof(uint64_t)); | ||
| hdl->info.timerfd.num_expirations = 0; | ||
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| /* perform a read (not supposed to block) to clear the event from writing/polling threads */ | ||
| if (hdl->info.timerfd.dummy_host_val) { | ||
| timerfd_dummy_host_read(hdl, /*out_host_val=*/NULL); | ||
| hdl->info.timerfd.dummy_host_val = 0; | ||
| } | ||
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| ret = (ssize_t)count; | ||
| out: | ||
| spinlock_unlock(&hdl->info.timerfd.expiration_lock); | ||
| maybe_epoll_et_trigger(hdl, ret, /*in=*/true, /*unused was_partial=*/false); | ||
| return ret; | ||
| } | ||
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| static void timerfd_post_poll(struct libos_handle* hdl, pal_wait_flags_t* pal_ret_events) { | ||
| assert(hdl->type == TYPE_TIMERFD); | ||
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| if (*pal_ret_events & (PAL_WAIT_ERROR | PAL_WAIT_HANG_UP)) { | ||
| /* impossible: we control eventfd inside the LibOS, and we never raise such conditions */ | ||
| BUG(); | ||
| } | ||
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| spinlock_lock(&hdl->info.timerfd.expiration_lock); | ||
| if (*pal_ret_events & PAL_WAIT_READ) { | ||
| /* there is data to read: verify if counter has value greater than zero */ | ||
| if (!hdl->info.timerfd.num_expirations) { | ||
| /* spurious or malicious notification -- for now we don't BUG but ignore it */ | ||
| *pal_ret_events &= ~PAL_WAIT_READ; | ||
| } | ||
| } | ||
| if (*pal_ret_events & PAL_WAIT_WRITE) { | ||
| /* spurious or malicious notification */ | ||
| BUG(); | ||
| } | ||
| spinlock_unlock(&hdl->info.timerfd.expiration_lock); | ||
| } | ||
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| static int timerfd_close(struct libos_handle* hdl) { | ||
| __UNUSED(hdl); | ||
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| /* see `libos_timerfd.c` for the handle-open counterpart */ | ||
| (void)__atomic_sub_fetch(&g_timerfd_cnt, 1, __ATOMIC_ACQ_REL); | ||
| return 0; | ||
| } | ||
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| struct libos_fs_ops timerfd_fs_ops = { | ||
| .read = &timerfd_read, | ||
| .close = &timerfd_close, | ||
| .post_poll = &timerfd_post_poll, | ||
| }; | ||
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| struct libos_fs timerfd_builtin_fs = { | ||
| .name = "timerfd", | ||
| .fs_ops = &timerfd_fs_ops, | ||
| }; |
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