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    Subject[RFC][PATCH v2 2/7] taskstats: Add "/proc/taskstats"
    From: Michael Holzheu <holzheu@linux.vnet.ibm.com>

    CHANGE HISTORY OF THIS PATCH
    ----------------------------
    Version 2
    ---------
    Replace ioctl interface with write interface (requested by Andrew Morton)

    The taskstats command is now set by one sys_write() with a buffer that
    contains first the taskstats command number (32 bit) and directly after that
    number the command payload.

    DESCRIPTION
    -----------
    Add procfs interface for the TASKSTATS_CMD_ATTR_PIDS taskstats command. A new
    procfs file "/proc/taskstats" is introduced. With sys_write() the taskstats
    command is defined. With a subsequent read system call the defined command
    is executed and the result of the command is transferred into the read buffer.
    This allows to get a complete and consistent snapshot with all tasks via two
    system calls (write + read), when a sufficiently large buffer is provided.
    This is not possible with the existing netlink interface, because there we
    have the socket buffer size as restricting factor.

    GOALS OF THIS PATCH
    -------------------
    * Allow transfer of a complete and consistent taskstats snapshot to user space.
    * Reduce CPU time for data transmission compared to netlink mechanism,
    because the proc solution is much more lightweight.
    * User space code is much easier to write compared to netlink mechanism.

    OPEN ISSUES
    -----------
    Currently only the TASKSTATS_CMD_ATTR_PIDS command is implemented. Implement
    the following missing taskstasts commands:
    * TASKSTATS_CMD_ATTR_PID
    * TASKSTATS_CMD_ATTR_TGID

    Signed-off-by: Michael Holzheu <holzheu@linux.vnet.ibm.com>
    ---
    include/linux/taskstats_kern.h | 3 +
    kernel/Makefile | 3 -
    kernel/taskstats.c | 1
    kernel/taskstats_proc.c | 107 +++++++++++++++++++++++++++++++++++++++++
    4 files changed, 113 insertions(+), 1 deletion(-)

    --- a/include/linux/taskstats_kern.h
    +++ b/include/linux/taskstats_kern.h
    @@ -32,6 +32,7 @@ extern void taskstats_fill_atomic(struct
    struct taskstats *stats);
    extern void taskstats_fill_sleep(struct task_struct *tsk,
    struct taskstats *stats);
    +extern void taskstats_proc_init(void);
    #else
    static inline void taskstats_exit(struct task_struct *tsk, int group_dead)
    {}
    @@ -39,6 +40,8 @@ static inline void taskstats_tgid_free(s
    {}
    static inline void taskstats_init_early(void)
    {}
    +static inline void taskstats_proc_init(void)
    +{}
    #endif /* CONFIG_TASKSTATS */

    #endif
    --- a/kernel/Makefile
    +++ b/kernel/Makefile
    @@ -90,7 +90,8 @@ obj-$(CONFIG_TINY_PREEMPT_RCU) += rcutin
    obj-$(CONFIG_RELAY) += relay.o
    obj-$(CONFIG_SYSCTL) += utsname_sysctl.o
    obj-$(CONFIG_TASK_DELAY_ACCT) += delayacct.o
    -obj-$(CONFIG_TASKSTATS) += taskstats.o tsacct.o taskstats_snap.o
    +obj-$(CONFIG_TASKSTATS) += taskstats.o tsacct.o taskstats_snap.o \
    + taskstats_proc.o
    obj-$(CONFIG_TRACEPOINTS) += tracepoint.o
    obj-$(CONFIG_LATENCYTOP) += latencytop.o
    obj-$(CONFIG_BINFMT_ELF) += elfcore.o
    --- a/kernel/taskstats.c
    +++ b/kernel/taskstats.c
    @@ -733,6 +733,7 @@ static int __init taskstats_init(void)
    rc = genl_register_ops(&family, &cgroupstats_ops);
    if (rc < 0)
    goto err_cgroup_ops;
    + taskstats_proc_init();
    family_registered = 1;
    printk("registered taskstats version %d\n", TASKSTATS_GENL_VERSION);
    return 0;
    --- /dev/null
    +++ b/kernel/taskstats_proc.c
    @@ -0,0 +1,107 @@
    +/*
    + * taskstats_proc.c - Export per-task statistics to userland using procfs
    + *
    + * Copyright IBM Corp. 2010
    + * Author(s): Michael Holzheu <holzheu@linux.vnet.ibm.com>
    + */
    +
    +#include <linux/taskstats_kern.h>
    +#include <linux/proc_fs.h>
    +#include <linux/kernel.h>
    +#include <linux/file.h>
    +#include <asm/uaccess.h>
    +
    +struct proc_cmd {
    + u32 no;
    + union {
    + struct taskstats_cmd_pids cmd_pids;
    + u32 pid;
    + } d;
    +};
    +
    +static ssize_t cmd_attr_pids_proc(struct taskstats *stats_vec,
    + struct taskstats_cmd_pids *cmd_pids)
    +{
    + int rc;
    +
    + rc = taskstats_snap_user(cmd_pids->pid, cmd_pids->cnt,
    + cmd_pids->time_ns, stats_vec);
    + if (rc < 0)
    + return rc;
    + else
    + return rc * sizeof(struct taskstats);
    +}
    +
    +static int proc_taskstats_open(struct inode *inode, struct file *file)
    +{
    + struct proc_cmd *proc_cmd;
    +
    + proc_cmd = kmalloc(sizeof(*proc_cmd), GFP_KERNEL);
    + if (!proc_cmd)
    + return -ENOMEM;
    + proc_cmd->no = -1;
    + file->private_data = proc_cmd;
    + return 0;
    +}
    +
    +static int proc_taskstats_close(struct inode *inode, struct file *file)
    +{
    + kfree(file->private_data);
    + return 0;
    +}
    +
    +static ssize_t proc_taskstats_write(struct file *file,
    + const char __user *buf, size_t count,
    + loff_t *ppos)
    +{
    + struct proc_cmd *proc_cmd = file->private_data;
    + u32 no;
    +
    + if (*ppos != 0)
    + return -EINVAL;
    + if (count < sizeof(no))
    + return -EINVAL;
    + if (copy_from_user(&no, buf, sizeof(no)))
    + return -EFAULT;
    + switch (no) {
    + case TASKSTATS_CMD_ATTR_PIDS:
    + if (count - sizeof(no) < sizeof(proc_cmd->d.cmd_pids))
    + return -EINVAL;
    + if (copy_from_user(&proc_cmd->d.cmd_pids, buf + sizeof(no),
    + sizeof(proc_cmd->d.cmd_pids)))
    + return -EFAULT;
    + break;
    + default:
    + return -EINVAL;
    + }
    + proc_cmd->no = no;
    + return count;
    +}
    +
    +static ssize_t proc_taskstats_read(struct file *file, char __user *buf,
    + size_t size, loff_t *ppos)
    +{
    + struct proc_cmd *proc_cmd = file->private_data;
    +
    + if (*ppos != 0)
    + return -EINVAL;
    + switch (proc_cmd->no) {
    + case TASKSTATS_CMD_ATTR_PIDS:
    + return cmd_attr_pids_proc((struct taskstats *) buf,
    + &proc_cmd->d.cmd_pids);
    + default:
    + return -EINVAL;
    + }
    +}
    +
    +static const struct file_operations proc_taskstats_ops = {
    + .open = proc_taskstats_open,
    + .release = proc_taskstats_close,
    + .read = proc_taskstats_read,
    + .write = proc_taskstats_write,
    +};
    +
    +void __init taskstats_proc_init(void)
    +{
    + proc_create("taskstats", 0666, NULL, &proc_taskstats_ops);
    +}


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