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Message-ID: <20140513024801.31728.qmail@ns.horizon.com>
Date: 12 May 2014 22:48:01 -0400
From: "George Spelvin" <linux@...izon.com>
To: john.stultz@...aro.org, linux@...izon.com
Cc: linux-kernel@...r.kernel.org, mathieu.desnoyers@...icios.com
Subject: [PATCH 2/2] timekeeping: Mark struct timekeeper * passed to notifiers as const
Add const delcarations where possible to make clear that the call chains
are not permitted to write to the structure.
It is not expected to improve generated code; the purpose is to document
the rules for who's allowed to modify the timekeeper state (and must
hold the associated locks) more clearly.
There are two code paths affected:
- update_vsyscall() (and update_vsyscall_old(), if used)
- update_pvclock_gtod() and the functions notified
This touches arch code that I have not tested, but only in a very safe
way: to add const declarations whose only effect is to add compile-time
complaints.
Signed-off-by: George Spelvin <linux@...izon.com>
---
One style issue: Some people prefer "const struct timekeeper *", when
I'm in the habit of writing "struct timekeeper const *". This is due
to an example I had pointed out to me:
typedef char *charp;
const char *a;
char const *b;
char * const c;
const charp d;
charp const e;
Which of these variables are the same type? The answer is that a and b
are writable pointers to const chars, while c through e are const pointers
to writeable chars. But if you're in the habit of writing const first,
a and d are easy to confuse. If you get in the habit of writing const
last, e looks like c, which is correct. Due to the typedef, there's
no way write a declaration with the const "between the char and the *"
that looks like b.
I found this persuasive, and have adopted the style. If it causes
violent reactions, I can change.
arch/arm64/kernel/vdso.c | 2 +-
arch/ia64/kernel/time.c | 2 +-
arch/powerpc/kernel/time.c | 2 +-
arch/s390/kernel/time.c | 2 +-
arch/tile/kernel/time.c | 2 +-
arch/x86/kernel/vsyscall_gtod.c | 2 +-
arch/x86/kvm/x86.c | 4 ++--
include/linux/timekeeper_internal.h | 10 +++++-----
kernel/time/timekeeping.c | 8 ++++----
9 files changed, 17 insertions(+), 17 deletions(-)
diff --git a/arch/arm64/kernel/vdso.c b/arch/arm64/kernel/vdso.c
index 50384fec56..dafdc36845 100644
--- a/arch/arm64/kernel/vdso.c
+++ b/arch/arm64/kernel/vdso.c
@@ -208,7 +208,7 @@ struct vm_area_struct *get_gate_vma(struct mm_struct *mm)
/*
* Update the vDSO data page to keep in sync with kernel timekeeping.
*/
-void update_vsyscall(struct timekeeper *tk)
+void update_vsyscall(struct timekeeper const *tk)
{
struct timespec xtime_coarse;
u32 use_syscall = strcmp(tk->clock->name, "arch_sys_counter");
diff --git a/arch/ia64/kernel/time.c b/arch/ia64/kernel/time.c
index 71c52bc7c2..353d5847f1 100644
--- a/arch/ia64/kernel/time.c
+++ b/arch/ia64/kernel/time.c
@@ -440,7 +440,7 @@ void update_vsyscall_tz(void)
{
}
-void update_vsyscall_old(struct timespec *wall, struct timespec *wtm,
+void update_vsyscall_old(struct timespec *wall, struct timespec const *wtm,
struct clocksource *c, u32 mult)
{
write_seqcount_begin(&fsyscall_gtod_data.seq);
diff --git a/arch/powerpc/kernel/time.c b/arch/powerpc/kernel/time.c
index 122a580f73..42ffd2309d 100644
--- a/arch/powerpc/kernel/time.c
+++ b/arch/powerpc/kernel/time.c
@@ -740,7 +740,7 @@ static cycle_t timebase_read(struct clocksource *cs)
return (cycle_t)get_tb();
}
-void update_vsyscall_old(struct timespec *wall_time, struct timespec *wtm,
+void update_vsyscall_old(struct timespec *wall_time, struct timespec const *wtm,
struct clocksource *clock, u32 mult)
{
u64 new_tb_to_xs, new_stamp_xsec;
diff --git a/arch/s390/kernel/time.c b/arch/s390/kernel/time.c
index 386d37a228..ea1c8d3137 100644
--- a/arch/s390/kernel/time.c
+++ b/arch/s390/kernel/time.c
@@ -210,7 +210,7 @@ struct clocksource * __init clocksource_default_clock(void)
return &clocksource_tod;
}
-void update_vsyscall(struct timekeeper *tk)
+void update_vsyscall(struct timekeeper const *tk)
{
u64 nsecps;
diff --git a/arch/tile/kernel/time.c b/arch/tile/kernel/time.c
index 462dcd0c17..7202570ad8 100644
--- a/arch/tile/kernel/time.c
+++ b/arch/tile/kernel/time.c
@@ -258,7 +258,7 @@ void update_vsyscall_tz(void)
++vdso_data->tz_update_count;
}
-void update_vsyscall(struct timekeeper *tk)
+void update_vsyscall(struct timekeeper const *tk)
{
struct timespec wall_time = tk_xtime(tk);
struct timespec *wtm = &tk->wall_to_monotonic;
diff --git a/arch/x86/kernel/vsyscall_gtod.c b/arch/x86/kernel/vsyscall_gtod.c
index f9c6e56e14..fa12766b38 100644
--- a/arch/x86/kernel/vsyscall_gtod.c
+++ b/arch/x86/kernel/vsyscall_gtod.c
@@ -24,7 +24,7 @@ void update_vsyscall_tz(void)
vsyscall_gtod_data.tz_dsttime = sys_tz.tz_dsttime;
}
-void update_vsyscall(struct timekeeper *tk)
+void update_vsyscall(struct timekeeper const *tk)
{
struct vsyscall_gtod_data *vdata = &vsyscall_gtod_data;
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 8b8fc0b792..0c42561f52 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1003,7 +1003,7 @@ struct pvclock_gtod_data {
static struct pvclock_gtod_data pvclock_gtod_data;
-static void update_pvclock_gtod(struct timekeeper *tk)
+static void update_pvclock_gtod(struct timekeeper const *tk)
{
struct pvclock_gtod_data *vdata = &pvclock_gtod_data;
@@ -5552,7 +5552,7 @@ static int pvclock_gtod_notify(struct notifier_block *nb, unsigned long unused,
void *priv)
{
struct pvclock_gtod_data *gtod = &pvclock_gtod_data;
- struct timekeeper *tk = priv;
+ struct timekeeper const *tk = priv;
update_pvclock_gtod(tk);
diff --git a/include/linux/timekeeper_internal.h b/include/linux/timekeeper_internal.h
index c1825eb436..96e39501d8 100644
--- a/include/linux/timekeeper_internal.h
+++ b/include/linux/timekeeper_internal.h
@@ -71,7 +71,7 @@ struct timekeeper {
};
-static inline struct timespec tk_xtime(struct timekeeper *tk)
+static inline struct timespec tk_xtime(struct timekeeper const *tk)
{
struct timespec ts;
@@ -83,16 +83,16 @@ static inline struct timespec tk_xtime(struct timekeeper *tk)
#ifdef CONFIG_GENERIC_TIME_VSYSCALL
-extern void update_vsyscall(struct timekeeper *tk);
+extern void update_vsyscall(struct timekeeper const *tk);
extern void update_vsyscall_tz(void);
#elif defined(CONFIG_GENERIC_TIME_VSYSCALL_OLD)
-extern void update_vsyscall_old(struct timespec *ts, struct timespec *wtm,
+extern void update_vsyscall_old(struct timespec *ts, struct timespec const *wtm,
struct clocksource *c, u32 mult);
extern void update_vsyscall_tz(void);
-static inline void update_vsyscall(struct timekeeper *tk)
+static inline void update_vsyscall(struct timekeeper const *tk)
{
struct timespec xt;
@@ -102,7 +102,7 @@ static inline void update_vsyscall(struct timekeeper *tk)
#else
-static inline void update_vsyscall(struct timekeeper *tk)
+static inline void update_vsyscall(struct timekeeper const *tk)
{
}
static inline void update_vsyscall_tz(void)
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 14e703e5bd..2e0fb0f617 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -165,7 +165,7 @@ u32 get_arch_timeoffset(void)
static inline u32 get_arch_timeoffset(void) { return 0; }
#endif
-static inline s64 timekeeping_get_ns(struct timekeeper *tk)
+static inline s64 timekeeping_get_ns(struct timekeeper const *tk)
{
cycle_t cycle_now, cycle_delta;
struct clocksource *clock;
@@ -185,7 +185,7 @@ static inline s64 timekeeping_get_ns(struct timekeeper *tk)
return nsec + get_arch_timeoffset();
}
-static inline s64 timekeeping_get_ns_raw(struct timekeeper *tk)
+static inline s64 timekeeping_get_ns_raw(struct timekeeper const *tk)
{
cycle_t cycle_now, cycle_delta;
struct clocksource *clock;
@@ -207,9 +207,9 @@ static inline s64 timekeeping_get_ns_raw(struct timekeeper *tk)
static RAW_NOTIFIER_HEAD(pvclock_gtod_chain);
-static void update_pvclock_gtod(struct timekeeper *tk, bool was_set)
+static void update_pvclock_gtod(struct timekeeper const *tk, bool was_set)
{
- raw_notifier_call_chain(&pvclock_gtod_chain, was_set, tk);
+ raw_notifier_call_chain(&pvclock_gtod_chain, was_set, (void *)tk);
}
/**
--
1.9.2
--
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