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Subject[PATCH v2] posix-timers: add multi_clock_gettime system call
Date
 Some user space applications need to read some clocks.
Each read requires moving from user space to kernel space.
This asymmetry causes the measured offset to have a significant error.

Introduce a new system call multi_clock_gettime, which can be used to measure
the offset between multiple clocks, from variety of types: PHC, virtual PHC
and various system clocks (CLOCK_REALTIME, CLOCK_MONOTONIC, etc).
The offset includes the total time that the driver needs to read the clock
timestamp.

New system call allows the reading of a list of clocks - up to PTP_MAX_CLOCKS.
Supported clocks IDs: PHC, virtual PHC and various system clocks.
Up to PTP_MAX_SAMPLES times (per clock) in a single system call read.
The system call returns n_clocks timestamps for each measurement:
- clock 0 timestamp
- ...
- clock n timestamp

Signed-off-by: Sagi Maimon <maimon.sagi@gmail.com>
---
Addressed comments from:
- Richard Cochran : https://www.spinics.net/lists/netdev/msg951723.html

Changes since version 1:
- Change multi PHC ioctl implamantation into systemcall.

arch/x86/entry/syscalls/syscall_32.tbl | 1 +
arch/x86/entry/syscalls/syscall_64.tbl | 1 +
include/linux/posix-timers.h | 24 ++++++++++
include/linux/syscalls.h | 3 +-
include/uapi/asm-generic/unistd.h | 12 ++++-
kernel/sys_ni.c | 1 +
kernel/time/posix-timers.c | 62 ++++++++++++++++++++++++++
7 files changed, 102 insertions(+), 2 deletions(-)

diff --git a/arch/x86/entry/syscalls/syscall_32.tbl b/arch/x86/entry/syscalls/syscall_32.tbl
index c8fac5205803..070efd266e7e 100644
--- a/arch/x86/entry/syscalls/syscall_32.tbl
+++ b/arch/x86/entry/syscalls/syscall_32.tbl
@@ -461,3 +461,4 @@
454 i386 futex_wake sys_futex_wake
455 i386 futex_wait sys_futex_wait
456 i386 futex_requeue sys_futex_requeue
+457 i386 multi_clock_gettime sys_multi_clock_gettime32
\ No newline at end of file
diff --git a/arch/x86/entry/syscalls/syscall_64.tbl b/arch/x86/entry/syscalls/syscall_64.tbl
index 8cb8bf68721c..f790330244bb 100644
--- a/arch/x86/entry/syscalls/syscall_64.tbl
+++ b/arch/x86/entry/syscalls/syscall_64.tbl
@@ -378,6 +378,7 @@
454 common futex_wake sys_futex_wake
455 common futex_wait sys_futex_wait
456 common futex_requeue sys_futex_requeue
+457 common multi_clock_gettime sys_multi_clock_gettime

#
# Due to a historical design error, certain syscalls are numbered differently
diff --git a/include/linux/posix-timers.h b/include/linux/posix-timers.h
index d607f51404fc..426a45441ab5 100644
--- a/include/linux/posix-timers.h
+++ b/include/linux/posix-timers.h
@@ -260,4 +260,28 @@ void set_process_cpu_timer(struct task_struct *task, unsigned int clock_idx,
int update_rlimit_cpu(struct task_struct *task, unsigned long rlim_new);

void posixtimer_rearm(struct kernel_siginfo *info);
+
+#define MULTI_PTP_MAX_CLOCKS 12 /* Max number of clocks */
+#define MULTI_PTP_MAX_SAMPLES 10 /* Max allowed offset measurement samples. */
+
+struct __ptp_multi_clock_get {
+ unsigned int n_clocks; /* Desired number of clocks. */
+ unsigned int n_samples; /* Desired number of measurements per clock. */
+ const clockid_t clkid_arr[MULTI_PTP_MAX_CLOCKS]; /* list of clock IDs */
+ /*
+ * Array of list of n_clocks clocks time samples n_samples times.
+ */
+ struct __kernel_timespec ts[MULTI_PTP_MAX_SAMPLES][MULTI_PTP_MAX_CLOCKS];
+};
+
+struct __ptp_multi_clock_get32 {
+ unsigned int n_clocks; /* Desired number of clocks. */
+ unsigned int n_samples; /* Desired number of measurements per clock. */
+ const clockid_t clkid_arr[MULTI_PTP_MAX_CLOCKS]; /* list of clock IDs */
+ /*
+ * Array of list of n_clocks clocks time samples n_samples times.
+ */
+ struct old_timespec32 ts[MULTI_PTP_MAX_SAMPLES][MULTI_PTP_MAX_CLOCKS];
+};
+
#endif
diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index fd9d12de7e92..afcf68e83d63 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -1161,7 +1161,8 @@ asmlinkage long sys_mmap_pgoff(unsigned long addr, unsigned long len,
unsigned long prot, unsigned long flags,
unsigned long fd, unsigned long pgoff);
asmlinkage long sys_old_mmap(struct mmap_arg_struct __user *arg);
-
+asmlinkage long sys_multi_clock_gettime(struct __ptp_multi_clock_get __user * ptp_multi_clk_get);
+asmlinkage long sys_multi_clock_gettime32(struct __ptp_multi_clock_get32 __user * ptp_multi_clk_get);

/*
* Not a real system call, but a placeholder for syscalls which are
diff --git a/include/uapi/asm-generic/unistd.h b/include/uapi/asm-generic/unistd.h
index 756b013fb832..3ebcaa052650 100644
--- a/include/uapi/asm-generic/unistd.h
+++ b/include/uapi/asm-generic/unistd.h
@@ -829,8 +829,18 @@ __SYSCALL(__NR_futex_wait, sys_futex_wait)
#define __NR_futex_requeue 456
__SYSCALL(__NR_futex_requeue, sys_futex_requeue)

+#if defined(__ARCH_WANT_TIME32_SYSCALLS) || __BITS_PER_LONG != 32
+#define __NR_multi_clock_gettime 457
+__SC_3264(__NR_multi_clock_gettime, sys_multi_clock_gettime32, sys_multi_clock_gettime)
+#endif
+
+#if defined(__SYSCALL_COMPAT) || __BITS_PER_LONG == 32
+#define __NR_multi_clock_gettime64 458
+__SYSCALL(__NR_multi_clock_gettime64, sys_multi_clock_gettime)
+#endif
+
#undef __NR_syscalls
-#define __NR_syscalls 457
+#define __NR_syscalls 459

/*
* 32 bit systems traditionally used different
diff --git a/kernel/sys_ni.c b/kernel/sys_ni.c
index e1a6e3c675c0..8ed1c22f40ac 100644
--- a/kernel/sys_ni.c
+++ b/kernel/sys_ni.c
@@ -335,6 +335,7 @@ COND_SYSCALL(ppoll_time32);
COND_SYSCALL_COMPAT(ppoll_time32);
COND_SYSCALL(utimensat_time32);
COND_SYSCALL(clock_adjtime32);
+COND_SYSCALL(multi_clock_gettime32);

/*
* The syscalls below are not found in include/uapi/asm-generic/unistd.h
diff --git a/kernel/time/posix-timers.c b/kernel/time/posix-timers.c
index b924f0f096fa..517558af2479 100644
--- a/kernel/time/posix-timers.c
+++ b/kernel/time/posix-timers.c
@@ -1426,6 +1426,68 @@ SYSCALL_DEFINE4(clock_nanosleep_time32, clockid_t, which_clock, int, flags,

#endif

+SYSCALL_DEFINE1(multi_clock_gettime, struct __ptp_multi_clock_get __user *, ptp_multi_clk_get)
+{
+ const struct k_clock *kc;
+ struct timespec64 kernel_tp;
+ struct __ptp_multi_clock_get multi_clk_get;
+ int error;
+ unsigned int i, j;
+
+ if (copy_from_user(&multi_clk_get, ptp_multi_clk_get, sizeof(multi_clk_get)))
+ return -EFAULT;
+
+ if (multi_clk_get.n_samples > MULTI_PTP_MAX_SAMPLES)
+ return -EINVAL;
+ if (multi_clk_get.n_clocks > MULTI_PTP_MAX_CLOCKS)
+ return -EINVAL;
+
+ for (j = 0; j < multi_clk_get.n_samples; j++) {
+ for (i = 0; i < multi_clk_get.n_clocks; i++) {
+ kc = clockid_to_kclock(multi_clk_get.clkid_arr[i]);
+ if (!kc)
+ return -EINVAL;
+ error = kc->clock_get_timespec(multi_clk_get.clkid_arr[i], &kernel_tp);
+ if (!error && put_timespec64(&kernel_tp, (struct __kernel_timespec __user *)
+ &ptp_multi_clk_get->ts[j][i]))
+ error = -EFAULT;
+ }
+ }
+
+ return error;
+}
+
+SYSCALL_DEFINE1(multi_clock_gettime32, struct __ptp_multi_clock_get32 __user *, ptp_multi_clk_get)
+{
+ const struct k_clock *kc;
+ struct timespec64 kernel_tp;
+ struct __ptp_multi_clock_get multi_clk_get;
+ int error;
+ unsigned int i, j;
+
+ if (copy_from_user(&multi_clk_get, ptp_multi_clk_get, sizeof(multi_clk_get)))
+ return -EFAULT;
+
+ if (multi_clk_get.n_samples > MULTI_PTP_MAX_SAMPLES)
+ return -EINVAL;
+ if (multi_clk_get.n_clocks > MULTI_PTP_MAX_CLOCKS)
+ return -EINVAL;
+
+ for (j = 0; j < multi_clk_get.n_samples; j++) {
+ for (i = 0; i < multi_clk_get.n_clocks; i++) {
+ kc = clockid_to_kclock(multi_clk_get.clkid_arr[i]);
+ if (!kc)
+ return -EINVAL;
+ error = kc->clock_get_timespec(multi_clk_get.clkid_arr[i], &kernel_tp);
+ if (!error && put_old_timespec32(&kernel_tp, (struct old_timespec32 __user *)
+ &ptp_multi_clk_get->ts[j][i]))
+ error = -EFAULT;
+ }
+ }
+
+ return error;
+}
+
static const struct k_clock clock_realtime = {
.clock_getres = posix_get_hrtimer_res,
.clock_get_timespec = posix_get_realtime_timespec,
--
2.26.3
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