Messages in this thread Patch in this message | | | Date | Wed, 7 Dec 2011 13:41:44 +0400 | From | Cyrill Gorcunov <> | Subject | Re: [PATCH] fs, proc: Introduce the /proc/<pid>/children entry v2 |
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On Wed, Dec 07, 2011 at 02:35:58AM +0400, Cyrill Gorcunov wrote: > On Tue, Dec 06, 2011 at 02:33:13PM -0800, Andrew Morton wrote: > ... > > > > It's also worth adding a warning about this into the documentation for > > this procfs file. Documentation which this patch forgot to provide, > > btw! > > > > > > Yes, thanks for comments Andrew, I already got the feeling that I've > missed documentation update from the start_brk /proc patch ;) > > I'll address all issues, thanks! >
I hope this one addresses all nits.
Cyrill --- From: Cyrill Gorcunov <gorcunov@openvz.org> Subject: [PATCH] fs, proc: Introduce the /proc/<pid>/children entry v3
There is no easy way to make a reverse parent->children chain from a task status, in turn children->parent provided with "PPid" field.
So instead of walking over all pids in system to figure out what children a task have -- we add explicit /proc/<pid>/children entry, since kernel already has this kind of information but it is not yet exported.
Note that filling user-space buffer is done in iterative manner where each iteration is protected via RCU read lock, which means if between iterations a new task is added it might be missed in output and to have a consistent image of which children are really present in system the task should be either frozen or stopped together with all children.
v2: - Kame suggested to use a separated /proc/<pid>/children entry instead of poking /proc/<pid>/status - Andew suggested to use rcu facility instead of locking tasklist_lock - Tejun pointed that non-seekable seq file might not be enough for tasks with large number of children
v3: - To be on a safe side use %lu format for pid_t printing - Update changelog and documentation
Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Pavel Emelyanov <xemul@parallels.com> Cc: Serge Hallyn <serge.hallyn@canonical.com> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Cc: Pavel Emelyanov <xemul@parallels.com> --- Documentation/filesystems/proc.txt | 15 ++++++++ fs/proc/array.c | 66 +++++++++++++++++++++++++++++++++++++ fs/proc/base.c | 1 fs/proc/internal.h | 1 4 files changed, 83 insertions(+)
Index: linux-2.6.git/Documentation/filesystems/proc.txt =================================================================== --- linux-2.6.git.orig/Documentation/filesystems/proc.txt +++ linux-2.6.git/Documentation/filesystems/proc.txt @@ -40,6 +40,7 @@ Table of Contents 3.4 /proc/<pid>/coredump_filter - Core dump filtering settings 3.5 /proc/<pid>/mountinfo - Information about mounts 3.6 /proc/<pid>/comm & /proc/<pid>/task/<tid>/comm + 3.7 /proc/<pid>/children - Information about task children ------------------------------------------------------------------------------ @@ -1545,3 +1546,17 @@ a task to set its own or one of its thre 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. + +3.7 /proc/<pid>/children - Information about task children +-------------------------------------------------------------- +This file provides a fast way to retrieve children pids of the +task pointed by <pid>. The format is a stream of pids separated +by space with a new line at the end. If a task has no children at +all -- only a new line returned. + +Note that filling user-space buffer is done in iterative manner where +each iteration is protected via RCU read lock, which means if between +iterations a new task is added it might be missed in output and +to have a consistent image of which children are really present in +system the task should be either frozen or stopped together with +all children. Index: linux-2.6.git/fs/proc/array.c =================================================================== --- linux-2.6.git.orig/fs/proc/array.c +++ linux-2.6.git/fs/proc/array.c @@ -547,3 +547,69 @@ int proc_pid_statm(struct seq_file *m, s return 0; } + +static int children_seq_show(struct seq_file *seq, void *v) +{ + struct task_struct *task = container_of(v, struct task_struct, sibling); + return seq_printf(seq, " %lu", (unsigned long)pid_vnr(task_pid(task))); +} + +static void *children_seq_start(struct seq_file *seq, loff_t *pos) +{ + struct task_struct *task; + + rcu_read_lock(); + task = seq->private; + if (task) + return seq_list_start(&task->children, *pos); + + return NULL; +} + +static void *children_seq_next(struct seq_file *seq, void *v, loff_t *pos) +{ + struct task_struct *task = seq->private; + if (task) + return seq_list_next(v, &task->children, pos); + return NULL; +} + +static void children_seq_stop(struct seq_file *seq, void *v) +{ + rcu_read_unlock(); + seq_printf(seq, "\n"); +} + +static const struct seq_operations children_seq_ops = { + .start = children_seq_start, + .next = children_seq_next, + .stop = children_seq_stop, + .show = children_seq_show, +}; + +static int children_seq_open(struct inode *inode, struct file *file) +{ + int ret = seq_open(file, &children_seq_ops); + if (!ret) { + struct seq_file *m = file->private_data; + m->private = (void *)get_proc_task(inode); + } + + return ret; +} +int children_seq_release(struct inode *inode, struct file *file) +{ + struct seq_file *m = file->private_data; + if (m->private) + put_task_struct(m->private); + + seq_release(inode, file); + return 0; +} + +const struct file_operations proc_pid_children_operations = { + .open = children_seq_open, + .read = seq_read, + .llseek = seq_lseek, + .release = children_seq_release, +}; Index: linux-2.6.git/fs/proc/base.c =================================================================== --- linux-2.6.git.orig/fs/proc/base.c +++ linux-2.6.git/fs/proc/base.c @@ -3204,6 +3204,7 @@ static const struct pid_entry tgid_base_ INF("cmdline", S_IRUGO, proc_pid_cmdline), ONE("stat", S_IRUGO, proc_tgid_stat), ONE("statm", S_IRUGO, proc_pid_statm), + REG("children", S_IRUGO, proc_pid_children_operations), REG("maps", S_IRUGO, proc_maps_operations), #ifdef CONFIG_NUMA REG("numa_maps", S_IRUGO, proc_numa_maps_operations), Index: linux-2.6.git/fs/proc/internal.h =================================================================== --- linux-2.6.git.orig/fs/proc/internal.h +++ linux-2.6.git/fs/proc/internal.h @@ -53,6 +53,7 @@ extern int proc_pid_statm(struct seq_fil struct pid *pid, struct task_struct *task); extern loff_t mem_lseek(struct file *file, loff_t offset, int orig); +extern const struct file_operations proc_pid_children_operations; extern const struct file_operations proc_maps_operations; extern const struct file_operations proc_numa_maps_operations; extern const struct file_operations proc_smaps_operations;
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