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SubjectRe: [RFC PATCH v2] taskstats: add /proc/taskstats to fetch pid/tgid status
Hi David,

Could you help review this patch ?

thanks

On Fri, Dec 18, 2020 at 1:24 AM Weiping Zhang
<zhangweiping@didiglobal.com> wrote:
>
> If a program needs monitor lots of process's status, it needs two
> syscalls for every process. The first one is telling kernel which
> pid/tgid should be monitored by send a command(write socket) to kernel.
> The second one is read the statistics by read socket. This patch add
> a new interface /proc/taskstats to reduce two syscalls to one ioctl.
> The user just set the target pid/tgid to the struct taskstats.ac_pid,
> then kernel will collect statistics for that pid/tgid.
>
> Signed-off-by: Weiping Zhang <zhangweiping@didiglobal.com>
> ---
> Changes since v1:
> * use /proc/taskstats instead of /dev/taskstats
>
> include/uapi/linux/taskstats.h | 5 +++
> kernel/taskstats.c | 73 +++++++++++++++++++++++++++++++++-
> 2 files changed, 77 insertions(+), 1 deletion(-)
>
> diff --git a/include/uapi/linux/taskstats.h b/include/uapi/linux/taskstats.h
> index ccbd08709321..077eab84c77e 100644
> --- a/include/uapi/linux/taskstats.h
> +++ b/include/uapi/linux/taskstats.h
> @@ -214,6 +214,11 @@ enum {
>
> #define TASKSTATS_CMD_ATTR_MAX (__TASKSTATS_CMD_ATTR_MAX - 1)
>
> +/* ioctl command */
> +#define TASKSTATS_IOC_ATTR_PID _IO('T', TASKSTATS_CMD_ATTR_PID)
> +#define TASKSTATS_IOC_ATTR_TGID _IO('T', TASKSTATS_CMD_ATTR_TGID)
> +
> +
> /* NETLINK_GENERIC related info */
>
> #define TASKSTATS_GENL_NAME "TASKSTATS"
> diff --git a/kernel/taskstats.c b/kernel/taskstats.c
> index a2802b6ff4bb..c0f9e2f2308b 100644
> --- a/kernel/taskstats.c
> +++ b/kernel/taskstats.c
> @@ -21,6 +21,8 @@
> #include <net/genetlink.h>
> #include <linux/atomic.h>
> #include <linux/sched/cputime.h>
> +#include <linux/proc_fs.h>
> +#include <linux/uio.h>
>
> /*
> * Maximum length of a cpumask that can be specified in
> @@ -28,6 +30,10 @@
> */
> #define TASKSTATS_CPUMASK_MAXLEN (100+6*NR_CPUS)
>
> +#ifdef CONFIG_PROC_FS
> +#define PROC_TASKSTATS "taskstats"
> +#endif
> +
> static DEFINE_PER_CPU(__u32, taskstats_seqnum);
> static int family_registered;
> struct kmem_cache *taskstats_cache;
> @@ -666,6 +672,60 @@ static struct genl_family family __ro_after_init = {
> .n_ops = ARRAY_SIZE(taskstats_ops),
> };
>
> +#ifdef CONFIG_PROC_FS
> +static long taskstats_ioctl_pid_tgid(unsigned long arg, bool tgid)
> +{
> + struct taskstats kstat;
> + struct taskstats *ustat = (struct taskstats *)arg;
> + u32 id;
> + unsigned long offset = offsetof(struct taskstats, ac_pid);
> + long ret;
> +
> + /* userspace set monitored pid/tgid to the field "ac_pid" */
> + if (unlikely(copy_from_user(&id, (void *)(arg + offset), sizeof(u32))))
> + return -EFAULT;
> +
> + if (tgid)
> + ret = fill_stats_for_tgid(id, &kstat);
> + else
> + ret = fill_stats_for_pid(id, &kstat);
> + if (ret < 0)
> + return ret;
> +
> + if (unlikely(copy_to_user(ustat, &kstat, sizeof(struct taskstats))))
> + return -EFAULT;
> +
> + return 0;
> +}
> +
> +static long taskstats_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
> +{
> + long ret;
> +
> + switch (cmd) {
> + case TASKSTATS_IOC_ATTR_PID:
> + ret = taskstats_ioctl_pid_tgid(arg, false);
> + break;
> + case TASKSTATS_IOC_ATTR_TGID:
> + ret = taskstats_ioctl_pid_tgid(arg, true);
> + break;
> + default:
> + ret = -EINVAL;
> + break;
> + }
> +
> + return ret;
> +}
> +
> +static const struct proc_ops taskstats_proc_ops = {
> + .proc_ioctl = taskstats_ioctl,
> +#ifdef CONFIG_COMPAT
> + .proc_compat_ioctl = taskstats_ioctl,
> +#endif
> +};
> +#endif
> +
> +
> /* Needed early in initialization */
> void __init taskstats_init_early(void)
> {
> @@ -682,9 +742,20 @@ static int __init taskstats_init(void)
> {
> int rc;
>
> +#ifdef CONFIG_PROC_FS
> + if (!proc_create(PROC_TASKSTATS, 0, NULL, &taskstats_proc_ops)) {
> + pr_err("failed to create /proc/%s\n", PROC_TASKSTATS);
> + return -1;
> + }
> +#endif
> +
> rc = genl_register_family(&family);
> - if (rc)
> + if (rc) {
> +#ifdef CONFIG_PROC_FS
> + remove_proc_entry(PROC_TASKSTATS, NULL);
> +#endif
> return rc;
> + }
>
> family_registered = 1;
> pr_info("registered taskstats version %d\n", TASKSTATS_GENL_VERSION);
> --
> 2.17.2
>

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