[RFC][PATCH 1/4] Provide a new procfs interface to set next id

[Nadia.Derbey-6ktuUTfB/bM@public.gmane.org]

[-- Attachment #1: proc_set_next_id.patch --]
[-- Type: text/plain, Size: 7376 bytes --]

[PATCH 01/04]

This patch proposes the procfs facilities needed to feed the id for the
next object to be allocated.

if an
echo "LONG XX" > /proc/self/next_id
is issued, next object to be created will have XX as its id.

This applies to objects that need a single id, such as ipc objects.

Signed-off-by: Nadia Derbey <Nadia.Derbey-6ktuUTfB/bM@public.gmane.org>

---
 fs/proc/base.c         |   73 +++++++++++++++++++++++++++++++++++++++++++++++++
 include/linux/sched.h  |    3 ++
 include/linux/sysids.h |   18 ++++++++++++
 kernel/Makefile        |    2 -
 kernel/fork.c          |    2 +
 kernel/nextid.c        |   69 ++++++++++++++++++++++++++++++++++++++++++++++
 6 files changed, 166 insertions(+), 1 deletion(-)

Index: linux-2.6.25-rc3-mm1/include/linux/sysids.h
===================================================================
--- /dev/null	1970-01-01 00:00:00.000000000 +0000
+++ linux-2.6.25-rc3-mm1/include/linux/sysids.h	2008-03-27 18:02:08.000000000 +0100
@@ -0,0 +1,18 @@
+/*
+ * include/linux/sysids.h
+ *
+ * Definitions to support object creation with predefined id.
+ *
+ */
+
+#ifndef _LINUX_SYSIDS_H
+#define _LINUX_SYSIDS_H
+
+struct sys_id {
+	long id;
+};
+
+extern ssize_t get_nextid(struct task_struct *, char *);
+extern int set_nextid(struct task_struct *, char *);
+
+#endif /* _LINUX_SYSIDS_H */
Index: linux-2.6.25-rc3-mm1/include/linux/sched.h
===================================================================
--- linux-2.6.25-rc3-mm1.orig/include/linux/sched.h	2008-03-10 09:18:46.000000000 +0100
+++ linux-2.6.25-rc3-mm1/include/linux/sched.h	2008-03-10 09:28:30.000000000 +0100
@@ -87,6 +87,7 @@ struct sched_param {
 #include <linux/task_io_accounting.h>
 #include <linux/kobject.h>
 #include <linux/latencytop.h>
+#include <linux/sysids.h>
 
 #include <asm/processor.h>
 
@@ -1261,6 +1262,8 @@ struct task_struct {
 	int latency_record_count;
 	struct latency_record latency_record[LT_SAVECOUNT];
 #endif
+	/* Id to assign to the next resource to be created */
+	struct sys_id *next_id;
 };
 
 /*
Index: linux-2.6.25-rc3-mm1/fs/proc/base.c
===================================================================
--- linux-2.6.25-rc3-mm1.orig/fs/proc/base.c	2008-03-10 09:19:39.000000000 +0100
+++ linux-2.6.25-rc3-mm1/fs/proc/base.c	2008-03-21 12:03:09.000000000 +0100
@@ -1080,6 +1080,77 @@ static const struct file_operations proc
 #endif
 
 
+static ssize_t next_id_read(struct file *file, char __user *buf,
+				size_t count, loff_t *ppos)
+{
+	struct task_struct *task;
+	char *page;
+	ssize_t length;
+
+	task = get_proc_task(file->f_path.dentry->d_inode);
+	if (!task)
+		return -ESRCH;
+
+	if (count > PROC_BLOCK_SIZE)
+		count = PROC_BLOCK_SIZE;
+
+	length = -ENOMEM;
+	page = (char *) __get_free_page(GFP_TEMPORARY);
+	if (!page)
+		goto out;
+
+	length = get_nextid(task, (char *) page);
+	if (length >= 0)
+		length = simple_read_from_buffer(buf, count, ppos,
+						(char *)page, length);
+	free_page((unsigned long) page);
+
+out:
+	put_task_struct(task);
+	return length;
+}
+
+static ssize_t next_id_write(struct file *file, const char __user *buf,
+				size_t count, loff_t *ppos)
+{
+	struct inode *inode = file->f_path.dentry->d_inode;
+	char *page;
+	ssize_t length;
+
+	if (pid_task(proc_pid(inode), PIDTYPE_PID) != current)
+		return -EPERM;
+
+	if (count >= PAGE_SIZE)
+		count = PAGE_SIZE - 1;
+
+	if (*ppos != 0) {
+		/* No partial writes. */
+		return -EINVAL;
+	}
+	page = (char *)__get_free_page(GFP_TEMPORARY);
+	if (!page)
+		return -ENOMEM;
+	length = -EFAULT;
+	if (copy_from_user(page, buf, count))
+		goto out_free_page;
+
+	page[count] = '\0';
+
+	length = set_nextid(current, page);
+	if (!length)
+		length = count;
+
+out_free_page:
+	free_page((unsigned long) page);
+	return length;
+}
+
+static const struct file_operations proc_next_id_operations = {
+	.read		= next_id_read,
+	.write		= next_id_write,
+};
+
+
 #ifdef CONFIG_SCHED_DEBUG
 /*
  * Print out various scheduling related per-task fields:
@@ -2391,6 +2462,7 @@ static const struct pid_entry tgid_base_
 #ifdef CONFIG_TASK_IO_ACCOUNTING
 	INF("io",	S_IRUGO, pid_io_accounting),
 #endif
+	REG("next_id", S_IRUGO|S_IWUSR, next_id),
 };
 
 static int proc_tgid_base_readdir(struct file * filp,
@@ -2716,6 +2788,7 @@ static const struct pid_entry tid_base_s
 #ifdef CONFIG_FAULT_INJECTION
 	REG("make-it-fail", S_IRUGO|S_IWUSR, fault_inject),
 #endif
+	REG("next_id", S_IRUGO|S_IWUSR, next_id),
 };
 
 static int proc_tid_base_readdir(struct file * filp,
Index: linux-2.6.25-rc3-mm1/kernel/Makefile
===================================================================
--- linux-2.6.25-rc3-mm1.orig/kernel/Makefile	2008-03-10 09:19:01.000000000 +0100
+++ linux-2.6.25-rc3-mm1/kernel/Makefile	2008-03-20 17:29:50.000000000 +0100
@@ -9,7 +9,7 @@ obj-y     = sched.o fork.o exec_domain.o
 	    rcupdate.o extable.o params.o posix-timers.o \
 	    kthread.o wait.o kfifo.o sys_ni.o posix-cpu-timers.o mutex.o \
 	    hrtimer.o rwsem.o nsproxy.o srcu.o semaphore.o \
-	    notifier.o ksysfs.o pm_qos_params.o
+	    notifier.o ksysfs.o pm_qos_params.o nextid.o
 
 obj-$(CONFIG_SYSCTL_SYSCALL_CHECK) += sysctl_check.o
 obj-$(CONFIG_STACKTRACE) += stacktrace.o
Index: linux-2.6.25-rc3-mm1/kernel/nextid.c
===================================================================
--- /dev/null	1970-01-01 00:00:00.000000000 +0000
+++ linux-2.6.25-rc3-mm1/kernel/nextid.c	2008-03-27 18:02:08.000000000 +0100
@@ -0,0 +1,69 @@
+/*
+ * linux/kernel/nextid.c
+ *
+ *
+ * Provide the get_nextid() / set_nextid() routines
+ * (called from fs/proc/base.c).
+ * They allow to specify the id for the next resource to be allocated,
+ * instead of letting the allocator set it for us.
+ */
+
+#include <linux/sched.h>
+#include <linux/ctype.h>
+
+
+
+ssize_t get_nextid(struct task_struct *task, char *buffer)
+{
+	struct sys_id *sid;
+
+	sid = task->next_id;
+	if (!sid)
+		return snprintf(buffer, sizeof(buffer), "-1\n");
+
+	return snprintf(buffer, sizeof(buffer), "%ld\n", sid->id);
+}
+
+static int set_single_id(struct task_struct *task, char *buffer)
+{
+	struct sys_id *sid;
+	long next_id;
+	char *end;
+
+	next_id = simple_strtol(buffer, &end, 0);
+	if (end == buffer || (end && !isspace(*end)))
+		return -EINVAL;
+
+	sid = task->next_id;
+	if (!sid) {
+		sid = kzalloc(sizeof(*sid), GFP_KERNEL);
+		if (!sid)
+			return -ENOMEM;
+		task->next_id = sid;
+	}
+
+	sid->id = next_id;
+
+	return 0;
+}
+
+#define SINGLE_LONG "LONG"
+
+/*
+ * Parses a line written to /proc/self/next_id.
+ * this line has the following format:
+ * LONG id              --> a single id is specified
+ */
+int set_nextid(struct task_struct *task, char *buffer)
+{
+	char *token, *out = buffer;
+
+	token = strsep(&out, " ");
+	if (!token || !out)
+		return -EINVAL;
+
+	if (!strcmp(token, SINGLE_LONG))
+		return set_single_id(task, out);
+	else
+		return -EINVAL;
+}
Index: linux-2.6.25-rc3-mm1/kernel/fork.c
===================================================================
--- linux-2.6.25-rc3-mm1.orig/kernel/fork.c	2008-03-27 18:01:56.000000000 +0100
+++ linux-2.6.25-rc3-mm1/kernel/fork.c	2008-03-27 18:02:42.000000000 +0100
@@ -1166,6 +1166,8 @@ static struct task_struct *copy_process(
 	p->blocked_on = NULL; /* not blocked yet */
 #endif
 
+	p->next_id = NULL;
+
 	/* Perform scheduler related setup. Assign this task to a CPU. */
 	sched_fork(p, clone_flags);
 

--