[v1,1/6] RISC-V: hwprobe: Clarify cpus size parameter

Commit Message

Andrew Jones Oct. 11, 2023, 1:56 p.m. UTC

The "count" parameter associated with the 'cpus' parameter of the
hwprobe syscall is the size in bytes of 'cpus'. Naming it 'cpu_count'
may mislead users (it did me) to think it's the number of CPUs that
are or can be represented by 'cpus' instead. This is particularly
easy (IMO) to get wrong since 'cpus' is documented to be defined by
CPU_SET(3) and CPU_SET(3) also documents a CPU_COUNT() (the number
of CPUs in set) macro. CPU_SET(3) refers to the size of cpu sets
with 'setsize'. Adopt 'cpusetsize' for the hwprobe parameter and
specifically state it is in bytes in Documentation/riscv/hwprobe.rst
to clarify.

Reviewed-by: Palmer Dabbelt <[e-mail]>
Signed-off-by: Andrew Jones <[e-mail]>
---
 Documentation/riscv/hwprobe.rst  | 15 ++++++++-------
 arch/riscv/kernel/sys_riscv.c    | 14 +++++++-------
 arch/riscv/kernel/vdso/hwprobe.c | 10 +++++-----
 3 files changed, 20 insertions(+), 19 deletions(-)

Comments

Conor Dooley Oct. 12, 2023, 1:38 p.m. UTC | #1

On Wed, Oct 11, 2023 at 03:56:12PM +0200, Andrew Jones wrote:
> The "count" parameter associated with the 'cpus' parameter of the
> hwprobe syscall is the size in bytes of 'cpus'. Naming it 'cpu_count'
> may mislead users (it did me) to think it's the number of CPUs that
> are or can be represented by 'cpus' instead. This is particularly
> easy (IMO) to get wrong since 'cpus' is documented to be defined by
> CPU_SET(3) and CPU_SET(3) also documents a CPU_COUNT() (the number
> of CPUs in set) macro. CPU_SET(3) refers to the size of cpu sets
> with 'setsize'. Adopt 'cpusetsize' for the hwprobe parameter and
> specifically state it is in bytes in Documentation/riscv/hwprobe.rst
> to clarify.
> 
> Reviewed-by: Palmer Dabbelt <[e-mail]>
> Signed-off-by: Andrew Jones <[e-mail]>

Reviewed-by: Conor Dooley <[e-mail]>

Thanks,
Conor.

Patch

diff --git a/Documentation/riscv/hwprobe.rst b/Documentation/riscv/hwprobe.rst
index a52996b22f75..c57437e40ffb 100644
--- a/Documentation/riscv/hwprobe.rst
+++ b/Documentation/riscv/hwprobe.rst
@@ -12,7 +12,7 @@  is defined in <asm/hwprobe.h>::
     };
 
     long sys_riscv_hwprobe(struct riscv_hwprobe *pairs, size_t pair_count,
-                           size_t cpu_count, cpu_set_t *cpus,
+                           size_t cpusetsize, cpu_set_t *cpus,
                            unsigned int flags);
 
 The arguments are split into three groups: an array of key-value pairs, a CPU
@@ -20,12 +20,13 @@  set, and some flags. The key-value pairs are supplied with a count. Userspace
 must prepopulate the key field for each element, and the kernel will fill in the
 value if the key is recognized. If a key is unknown to the kernel, its key field
 will be cleared to -1, and its value set to 0. The CPU set is defined by
-CPU_SET(3). For value-like keys (eg. vendor/arch/impl), the returned value will
-be only be valid if all CPUs in the given set have the same value. Otherwise -1
-will be returned. For boolean-like keys, the value returned will be a logical
-AND of the values for the specified CPUs. Usermode can supply NULL for cpus and
-0 for cpu_count as a shortcut for all online CPUs. There are currently no flags,
-this value must be zero for future compatibility.
+CPU_SET(3) with size ``cpusetsize`` bytes. For value-like keys (eg. vendor,
+arch, impl), the returned value will only be valid if all CPUs in the given set
+have the same value. Otherwise -1 will be returned. For boolean-like keys, the
+value returned will be a logical AND of the values for the specified CPUs.
+Usermode can supply NULL for ``cpus`` and 0 for ``cpusetsize`` as a shortcut for
+all online CPUs. There are currently no flags, this value must be zero for
+future compatibility.
 
 On success 0 is returned, on failure a negative error code is returned.
 
diff --git a/arch/riscv/kernel/sys_riscv.c b/arch/riscv/kernel/sys_riscv.c
index 473159b5f303..ed3545eb1b2b 100644
--- a/arch/riscv/kernel/sys_riscv.c
+++ b/arch/riscv/kernel/sys_riscv.c
@@ -228,7 +228,7 @@  static void hwprobe_one_pair(struct riscv_hwprobe *pair,
 }
 
 static int do_riscv_hwprobe(struct riscv_hwprobe __user *pairs,
-			    size_t pair_count, size_t cpu_count,
+			    size_t pair_count, size_t cpusetsize,
 			    unsigned long __user *cpus_user,
 			    unsigned int flags)
 {
@@ -246,13 +246,13 @@  static int do_riscv_hwprobe(struct riscv_hwprobe __user *pairs,
 	 * 0 as a shortcut to all online CPUs.
 	 */
 	cpumask_clear(&cpus);
-	if (!cpu_count && !cpus_user) {
+	if (!cpusetsize && !cpus_user) {
 		cpumask_copy(&cpus, cpu_online_mask);
 	} else {
-		if (cpu_count > cpumask_size())
-			cpu_count = cpumask_size();
+		if (cpusetsize > cpumask_size())
+			cpusetsize = cpumask_size();
 
-		ret = copy_from_user(&cpus, cpus_user, cpu_count);
+		ret = copy_from_user(&cpus, cpus_user, cpusetsize);
 		if (ret)
 			return -EFAULT;
 
@@ -329,10 +329,10 @@  arch_initcall_sync(init_hwprobe_vdso_data);
 #endif /* CONFIG_MMU */
 
 SYSCALL_DEFINE5(riscv_hwprobe, struct riscv_hwprobe __user *, pairs,
-		size_t, pair_count, size_t, cpu_count, unsigned long __user *,
+		size_t, pair_count, size_t, cpusetsize, unsigned long __user *,
 		cpus, unsigned int, flags)
 {
-	return do_riscv_hwprobe(pairs, pair_count, cpu_count,
+	return do_riscv_hwprobe(pairs, pair_count, cpusetsize,
 				cpus, flags);
 }
 
diff --git a/arch/riscv/kernel/vdso/hwprobe.c b/arch/riscv/kernel/vdso/hwprobe.c
index cadf725ef798..026b7645c5ab 100644
--- a/arch/riscv/kernel/vdso/hwprobe.c
+++ b/arch/riscv/kernel/vdso/hwprobe.c
@@ -8,21 +8,21 @@ 
 #include <vdso/helpers.h>
 
 extern int riscv_hwprobe(struct riscv_hwprobe *pairs, size_t pair_count,
-			 size_t cpu_count, unsigned long *cpus,
+			 size_t cpusetsize, unsigned long *cpus,
 			 unsigned int flags);
 
 /* Add a prototype to avoid -Wmissing-prototypes warning. */
 int __vdso_riscv_hwprobe(struct riscv_hwprobe *pairs, size_t pair_count,
-			 size_t cpu_count, unsigned long *cpus,
+			 size_t cpusetsize, unsigned long *cpus,
 			 unsigned int flags);
 
 int __vdso_riscv_hwprobe(struct riscv_hwprobe *pairs, size_t pair_count,
-			 size_t cpu_count, unsigned long *cpus,
+			 size_t cpusetsize, unsigned long *cpus,
 			 unsigned int flags)
 {
 	const struct vdso_data *vd = __arch_get_vdso_data();
 	const struct arch_vdso_data *avd = &vd->arch_data;
-	bool all_cpus = !cpu_count && !cpus;
+	bool all_cpus = !cpusetsize && !cpus;
 	struct riscv_hwprobe *p = pairs;
 	struct riscv_hwprobe *end = pairs + pair_count;
 
@@ -33,7 +33,7 @@  int __vdso_riscv_hwprobe(struct riscv_hwprobe *pairs, size_t pair_count,
 	 * masks.
 	 */
 	if ((flags != 0) || (!all_cpus && !avd->homogeneous_cpus))
-		return riscv_hwprobe(pairs, pair_count, cpu_count, cpus, flags);
+		return riscv_hwprobe(pairs, pair_count, cpusetsize, cpus, flags);
 
 	/* This is something we can handle, fill out the pairs. */
 	while (p < end) {