Serge E. Hallyn wrote:
> Quoting Nadia.Derbey@bull.net (Nadia.Derbey@bull.net):
> 
>>[PATCH 01/05]
>>
>>This patch adds the procfs facility needed to feed some data for the
>>next syscall to be called.
>>
>>The effect of issuing
>>echo "LONG<Y> <XX>" > /proc/self/task/<tid>/next_syscall_data
>>is that <XX> will be stored in a new field of the task structure
>>(next_syscall_data). This field, in turn will be taken as the data to feed
>>next syscall that supports the feature.
>>
>><Y> is the number of values provided on the line.
>>For the sake of simplicity it is now fixed to 1, but this can be extended as
>>needed, in the future.
>>
>>This is particularly useful when restarting an application, as we need
>>sometimes the syscalls to have a non-default behavior.
>>
>>Signed-off-by: Nadia Derbey <Nadia.Derbey@bull.net>
>>
>>---
>> fs/exec.c                         |    6 +
>> fs/proc/base.c                    |   75 ++++++++++++++++++
>> include/linux/next_syscall_data.h |   35 ++++++++
>> include/linux/sched.h             |    6 +
>> kernel/Makefile                   |    3 
>> kernel/exit.c                     |    4 +
>> kernel/fork.c                     |    2 
>> kernel/next_syscall_data.c        |  151 ++++++++++++++++++++++++++++++++++++++
>> 8 files changed, 281 insertions(+), 1 deletion(-)
>>
>>Index: linux-2.6.26-rc5-mm3/include/linux/sched.h
>>===================================================================
>>--- linux-2.6.26-rc5-mm3.orig/include/linux/sched.h	2008-06-25 17:10:38.000000000 +0200
>>+++ linux-2.6.26-rc5-mm3/include/linux/sched.h	2008-06-27 14:18:56.000000000 +0200
>>@@ -87,6 +87,7 @@ struct sched_param {
>> #include <linux/task_io_accounting.h>
>> #include <linux/kobject.h>
>> #include <linux/latencytop.h>
>>+#include <linux/next_syscall_data.h>
>>
>> #include <asm/processor.h>
>>
>>@@ -1312,6 +1313,11 @@ struct task_struct {
>> 	int latency_record_count;
>> 	struct latency_record latency_record[LT_SAVECOUNT];
>> #endif
>>+	/*
>>+	 * If non-NULL indicates that next operation will be forced, e.g.
>>+	 * that next object to be created will have a predefined id.
>>+	 */
>>+	struct next_syscall_data *nsd;
>> };
>>
>> /*
>>Index: linux-2.6.26-rc5-mm3/include/linux/next_syscall_data.h
>>===================================================================
>>--- /dev/null	1970-01-01 00:00:00.000000000 +0000
>>+++ linux-2.6.26-rc5-mm3/include/linux/next_syscall_data.h	2008-07-01 10:25:48.000000000 +0200
>>@@ -0,0 +1,35 @@
>>+/*
>>+ * include/linux/next_syscall_data.h
>>+ *
>>+ * Definitions to support fixed data for next syscall to be called. The
>>+ * following is supported today:
>>+ *    . object creation with a predefined id.
>>+ *
>>+ */
>>+
>>+#ifndef _LINUX_NEXT_SYSCALL_DATA_H
>>+#define _LINUX_NEXT_SYSCALL_DATA_H
>>+
>>+#define NDATA 1
>>+
>>+/*
>>+ * If this structure is pointed to by a task_struct, next syscall to be called
>>+ * by the task will have a non-default behavior.
>>+ * For example, it can be used to pre-set the id of the object to be created
>>+ * by next syscall.
>>+ */
>>+struct next_syscall_data {
>>+	int ndata;
>>+	long data[NDATA];
>>+};
>>+
>>+extern ssize_t get_next_syscall_data(struct task_struct *, char *, size_t);
>>+extern int set_next_syscall_data(struct task_struct *, char *);
>>+extern int reset_next_syscall_data(struct task_struct *);
>>+
>>+static inline void exit_next_syscall_data(struct task_struct *tsk)
>>+{
>>+	reset_next_syscall_data(tsk);
>>+}
>>+
>>+#endif /* _LINUX_NEXT_SYSCALL_DATA_H */
>>Index: linux-2.6.26-rc5-mm3/fs/proc/base.c
>>===================================================================
>>--- linux-2.6.26-rc5-mm3.orig/fs/proc/base.c	2008-06-25 17:11:04.000000000 +0200
>>+++ linux-2.6.26-rc5-mm3/fs/proc/base.c	2008-07-01 09:09:30.000000000 +0200
>>@@ -1158,6 +1158,76 @@ static const struct file_operations proc
>> };
>> #endif
>>
>>+static ssize_t next_syscall_data_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 >= PAGE_SIZE)
>>+		count = PAGE_SIZE - 1;
>>+
>>+	length = -ENOMEM;
>>+	page = (char *) __get_free_page(GFP_TEMPORARY);
>>+	if (!page)
>>+		goto out;
>>+
>>+	length = get_next_syscall_data(task, (char *) page, count);
>>+	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_syscall_data_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_next_syscall_data(current, page);
>>+	if (!length)
>>+		length = count;
>>+
>>+out_free_page:
>>+	free_page((unsigned long) page);
>>+	return length;
>>+}
>>+
>>+static const struct file_operations proc_next_syscall_data_operations = {
>>+	.read		= next_syscall_data_read,
>>+	.write		= next_syscall_data_write,
>>+};
>>
>> #ifdef CONFIG_SCHED_DEBUG
>> /*
>>@@ -2853,6 +2923,11 @@ static const struct pid_entry tid_base_s
>> #ifdef CONFIG_TASK_IO_ACCOUNTING
>> 	INF("io",	S_IRUGO, tid_io_accounting),
>> #endif
>>+	/*
>>+	 * NOTE that this file is not added into tgid_base_stuff[] since it
>>+	 * has to be specified on a per-thread basis.
>>+	 */
>>+	REG("next_syscall_data", S_IRUGO|S_IWUSR, next_syscall_data),
>> };
>>
>> static int proc_tid_base_readdir(struct file * filp,
>>Index: linux-2.6.26-rc5-mm3/kernel/Makefile
>>===================================================================
>>--- linux-2.6.26-rc5-mm3.orig/kernel/Makefile	2008-06-25 17:10:41.000000000 +0200
>>+++ linux-2.6.26-rc5-mm3/kernel/Makefile	2008-06-27 09:03:01.000000000 +0200
>>@@ -9,7 +9,8 @@ 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 sched_clock.o
>>+	    notifier.o ksysfs.o pm_qos_params.o sched_clock.o \
>>+	    next_syscall_data.o
>>
>> CFLAGS_REMOVE_sched.o = -pg -mno-spe
>>
>>Index: linux-2.6.26-rc5-mm3/kernel/next_syscall_data.c
>>===================================================================
>>--- /dev/null	1970-01-01 00:00:00.000000000 +0000
>>+++ linux-2.6.26-rc5-mm3/kernel/next_syscall_data.c	2008-07-01 10:39:43.000000000 +0200
>>@@ -0,0 +1,151 @@
>>+/*
>>+ * linux/kernel/next_syscall_data.c
>>+ *
>>+ *
>>+ * Provide the get_next_syscall_data() / set_next_syscall_data() routines
>>+ * (called from fs/proc/base.c).
>>+ * They allow to specify some particular data for the next syscall to be
>>+ * called.
>>+ * E.g. they can be used 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_next_syscall_data(struct task_struct *task, char *buffer,
>>+				size_t size)
>>+{
>>+	struct next_syscall_data *nsd;
>>+	char *bufptr = buffer;
>>+	ssize_t rc, count = 0;
>>+	int i;
>>+
>>+	nsd = task->nsd;
>>+	if (!nsd || !nsd->ndata)
>>+		return snprintf(buffer, size, "UNSET\n");
>>+
>>+	count = snprintf(bufptr, size, "LONG%d ", nsd->ndata);
>>+
>>+	for (i = 0; i < nsd->ndata - 1; i++) {
>>+		rc = snprintf(&bufptr[count], size - count, "%ld ",
>>+				nsd->data[i]);
>>+		if (rc >= size - count)
>>+			return -ENOMEM;
>>+		count += rc;
>>+	}
>>+
>>+	rc = snprintf(&bufptr[count], size - count, "%ld\n", nsd->data[i]);
>>+	if (rc >= size - count)
>>+		return -ENOMEM;
>>+	count += rc;
>>+
>>+	return count;
>>+}
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