Re: + proc-export-a-processes-resource-limits-via-proc-pid.patch added to -mm tree

[Neil Horman <nhorman@tuxdriver.com>]

> 
> Neil, please, don't add tasklist_lock again. It was not easy to wipe it from
> fs/proc/ :) Just change this code to use rcu_read_lock().
> 

Ok, done/tested.  Thanks!

Currently, there exists no method for a process to query the resource
limits of another process.  They can be inferred via some mechanisms but they
cannot be explicitly determined.  Given that this information can be usefull to
know during the debugging of an application, I've written this patch which
exports all of a processes limits via /proc/<pid>/limits.  Tested successfully
by myself on x86 on top of 2.6.23-rc2-mm1.


Signed-off-by: Neil Horman <nhorman@tuxdriver.com>


 base.c |   77 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 77 insertions(+)


diff --git a/fs/proc/base.c b/fs/proc/base.c
index ed2b224..86130b0 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -74,6 +74,7 @@
 #include <linux/nsproxy.h>
 #include <linux/oom.h>
 #include <linux/elf.h>
+#include <linux/resource.h>
 #include "internal.h"
 
 /* NOTE:
@@ -323,6 +324,80 @@ static int proc_oom_score(struct task_struct *task, char *buffer)
 	return sprintf(buffer, "%lu\n", points);
 }
 
+struct limit_names {
+	char *name;
+	char *unit;
+};
+
+static const struct limit_names lnames[RLIM_NLIMITS] = {
+	[RLIMIT_CPU] = {"Max cpu time", "ms"},
+	[RLIMIT_FSIZE] = {"Max file size", "bytes"},
+	[RLIMIT_DATA] = {"Max data size", "bytes"},
+	[RLIMIT_STACK] = {"Max stack size", "bytes"},
+	[RLIMIT_CORE] = {"Max core file size", "bytes"},
+	[RLIMIT_RSS] = {"Max resident set", "bytes"},
+	[RLIMIT_NPROC] = {"Max processes", "processes"},
+	[RLIMIT_NOFILE] = {"Max open files", "files"},
+	[RLIMIT_MEMLOCK] = {"Max locked memory", "bytes"},
+	[RLIMIT_AS] = {"Max address space", "bytes"},
+	[RLIMIT_LOCKS] = {"Max file locks", "locks"},
+	[RLIMIT_SIGPENDING] = {"Max pending signals", "signals"},
+	[RLIMIT_MSGQUEUE] = {"Max msgqueue size", "bytes"},
+	[RLIMIT_NICE] = {"Max nice priority", NULL},
+	[RLIMIT_RTPRIO] = {"Max realtime priority", NULL},
+};
+
+/* Display limits for a process */
+static int proc_pid_limits(struct task_struct *task, char *buffer)
+{
+	unsigned int i;
+	int count = 0;
+	unsigned long flags;
+	char *bufptr = buffer;
+
+	struct rlimit rlim[RLIM_NLIMITS];
+
+	rcu_read_lock();
+	lock_task_sighand(task,&flags);
+	if (task->signal == NULL){
+		unlock_task_sighand(task, &flags);
+		rcu_read_unlock();
+		return 0;
+	}
+	memcpy(rlim, task->signal->rlim, sizeof(struct rlimit) * RLIM_NLIMITS);
+	unlock_task_sighand(task, &flags);
+	rcu_read_unlock();
+
+	/*
+	 * print the file header
+	 */
+	count += sprintf(&bufptr[count], "%-25s %-20s %-20s %-10s\n",
+			"Limit", "Soft Limit", "Hard Limit", "Units");
+
+	for (i = 0; i < RLIM_NLIMITS; i++) {
+		if (rlim[i].rlim_cur == RLIM_INFINITY)
+			count += sprintf(&bufptr[count], "%-25s %-20s ",
+					 lnames[i].name, "unlimited");
+		else
+			count += sprintf(&bufptr[count], "%-25s %-20lu ",
+					 lnames[i].name, rlim[i].rlim_cur);
+
+		if (rlim[i].rlim_max == RLIM_INFINITY)
+			count += sprintf(&bufptr[count], "%-20s ", "unlimited");
+		else
+			count += sprintf(&bufptr[count], "%-20lu ",
+					 rlim[i].rlim_max);
+
+		if (lnames[i].unit)
+			count += sprintf(&bufptr[count], "%-10s\n",
+					 lnames[i].unit);
+		else
+			count += sprintf(&bufptr[count], "\n");
+	}
+
+	return count;
+}
+
 /************************************************************************/
 /*                       Here the fs part begins                        */
 /************************************************************************/
@@ -2017,6 +2092,7 @@ static const struct pid_entry tgid_base_stuff[] = {
 	INF("environ",    S_IRUSR, pid_environ),
 	INF("auxv",       S_IRUSR, pid_auxv),
 	INF("status",     S_IRUGO, pid_status),
+	INF("limits",	  S_IRUSR, pid_limits),
 #ifdef CONFIG_SCHED_DEBUG
 	REG("sched",      S_IRUGO|S_IWUSR, pid_sched),
 #endif
@@ -2310,6 +2386,7 @@ static const struct pid_entry tid_base_stuff[] = {
 	INF("environ",   S_IRUSR, pid_environ),
 	INF("auxv",      S_IRUSR, pid_auxv),
 	INF("status",    S_IRUGO, pid_status),
+	INF("limits",	 S_IRUSR, pid_limits),
 #ifdef CONFIG_SCHED_DEBUG
 	REG("sched",     S_IRUGO|S_IWUSR, pid_sched),
 #endif
-- 
/***************************************************
 *Neil Horman
 *Software Engineer
 *Red Hat, Inc.
 *nhorman@tuxdriver.com
 *gpg keyid: 1024D / 0x92A74FA1
 *http://pgp.mit.edu
 ***************************************************/
-
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