From 4614a696bd1c3a9af3a08f0e5874830a85b889d4 Mon Sep 17 00:00:00 2001 From: john stultz Date: Mon, 14 Dec 2009 18:00:05 -0800 Subject: [PATCH] procfs: allow threads to rename siblings via /proc/pid/tasks/tid/comm Setting a thread's comm to be something unique is a very useful ability and is helpful for debugging complicated threaded applications. However currently the only way to set a thread name is for the thread to name itself via the PR_SET_NAME prctl. However, there may be situations where it would be advantageous for a thread dispatcher to be naming the threads its managing, rather then having the threads self-describe themselves. This sort of behavior is available on other systems via the pthread_setname_np() interface. This patch exports a task's comm via proc/pid/comm and proc/pid/task/tid/comm interfaces, and allows thread siblings to write to these values. [akpm@linux-foundation.org: cleanups] Signed-off-by: John Stultz Cc: Andi Kleen Cc: Arjan van de Ven Cc: Mike Fulton Cc: Sean Foley Cc: Darren Hart Cc: KOSAKI Motohiro Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- Documentation/filesystems/proc.txt | 9 ++++ fs/exec.c | 9 ++++ fs/proc/base.c | 68 ++++++++++++++++++++++++++++++ 3 files changed, 86 insertions(+) diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt index 94b9f2056f4c..220cc6376ef8 100644 --- a/Documentation/filesystems/proc.txt +++ b/Documentation/filesystems/proc.txt @@ -38,6 +38,7 @@ Table of Contents 3.3 /proc//io - Display the IO accounting fields 3.4 /proc//coredump_filter - Core dump filtering settings 3.5 /proc//mountinfo - Information about mounts + 3.6 /proc//comm & /proc//task//comm ------------------------------------------------------------------------------ @@ -1409,3 +1410,11 @@ For more information on mount propagation see: Documentation/filesystems/sharedsubtree.txt + +3.6 /proc//comm & /proc//task//comm +-------------------------------------------------------- +These files provide a method to access a tasks comm value. It also allows for +a task to set its own or one of its thread siblings comm value. The comm value +is limited in size compared to the cmdline value, so writing anything longer +then the kernel's TASK_COMM_LEN (currently 16 chars) will result in a truncated +comm value. diff --git a/fs/exec.c b/fs/exec.c index c0c636e34f60..623a5cc3076a 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -923,6 +923,15 @@ char *get_task_comm(char *buf, struct task_struct *tsk) void set_task_comm(struct task_struct *tsk, char *buf) { task_lock(tsk); + + /* + * Threads may access current->comm without holding + * the task lock, so write the string carefully. + * Readers without a lock may see incomplete new + * names but are safe from non-terminating string reads. + */ + memset(tsk->comm, 0, TASK_COMM_LEN); + wmb(); strlcpy(tsk->comm, buf, sizeof(tsk->comm)); task_unlock(tsk); perf_event_comm(tsk); diff --git a/fs/proc/base.c b/fs/proc/base.c index af643b5aefe8..4df4a464a919 100644 --- a/fs/proc/base.c +++ b/fs/proc/base.c @@ -1265,6 +1265,72 @@ static const struct file_operations proc_pid_sched_operations = { #endif +static ssize_t comm_write(struct file *file, const char __user *buf, + size_t count, loff_t *offset) +{ + struct inode *inode = file->f_path.dentry->d_inode; + struct task_struct *p; + char buffer[TASK_COMM_LEN]; + + memset(buffer, 0, sizeof(buffer)); + if (count > sizeof(buffer) - 1) + count = sizeof(buffer) - 1; + if (copy_from_user(buffer, buf, count)) + return -EFAULT; + + p = get_proc_task(inode); + if (!p) + return -ESRCH; + + if (same_thread_group(current, p)) + set_task_comm(p, buffer); + else + count = -EINVAL; + + put_task_struct(p); + + return count; +} + +static int comm_show(struct seq_file *m, void *v) +{ + struct inode *inode = m->private; + struct task_struct *p; + + p = get_proc_task(inode); + if (!p) + return -ESRCH; + + task_lock(p); + seq_printf(m, "%s\n", p->comm); + task_unlock(p); + + put_task_struct(p); + + return 0; +} + +static int comm_open(struct inode *inode, struct file *filp) +{ + int ret; + + ret = single_open(filp, comm_show, NULL); + if (!ret) { + struct seq_file *m = filp->private_data; + + m->private = inode; + } + return ret; +} + +static const struct file_operations proc_pid_set_comm_operations = { + .open = comm_open, + .read = seq_read, + .write = comm_write, + .llseek = seq_lseek, + .release = single_release, +}; + /* * We added or removed a vma mapping the executable. The vmas are only mapped * during exec and are not mapped with the mmap system call. @@ -2504,6 +2570,7 @@ static const struct pid_entry tgid_base_stuff[] = { #ifdef CONFIG_SCHED_DEBUG REG("sched", S_IRUGO|S_IWUSR, proc_pid_sched_operations), #endif + REG("comm", S_IRUGO|S_IWUSR, proc_pid_set_comm_operations), #ifdef CONFIG_HAVE_ARCH_TRACEHOOK INF("syscall", S_IRUSR, proc_pid_syscall), #endif @@ -2838,6 +2905,7 @@ static const struct pid_entry tid_base_stuff[] = { #ifdef CONFIG_SCHED_DEBUG REG("sched", S_IRUGO|S_IWUSR, proc_pid_sched_operations), #endif + REG("comm", S_IRUGO|S_IWUSR, proc_pid_set_comm_operations), #ifdef CONFIG_HAVE_ARCH_TRACEHOOK INF("syscall", S_IRUSR, proc_pid_syscall), #endif -- 2.20.1