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>

Acked-by: Serge Hallyn <serue@us.ibm.com>

thanks,
-serge

> 
> ---
>  fs/exec.c                         |    6 +
>  fs/proc/base.c                    |   75 ++++++++++++++++++
>  include/linux/next_syscall_data.h |   32 ++++++++
>  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, 278 insertions(+), 1 deletion(-)
> 
> Index: linux-2.6.26-rc8-mm1/include/linux/sched.h
> ===================================================================
> --- linux-2.6.26-rc8-mm1.orig/include/linux/sched.h	2008-07-08 09:04:21.000000000 +0200
> +++ linux-2.6.26-rc8-mm1/include/linux/sched.h	2008-07-08 09:13:43.000000000 +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>
> 
> @@ -1296,6 +1297,11 @@ 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-rc8-mm1/include/linux/next_syscall_data.h
> ===================================================================
> --- /dev/null	1970-01-01 00:00:00.000000000 +0000
> +++ linux-2.6.26-rc8-mm1/include/linux/next_syscall_data.h	2008-07-08 09:24:38.000000000 +0200
> @@ -0,0 +1,32 @@
> +/*
> + * include/linux/next_syscall_data.h
> + *
> + * Definitions to support fixed data for next syscall to be called.
> + */
> +
> +#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 void 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-rc8-mm1/fs/proc/base.c
> ===================================================================
> --- linux-2.6.26-rc8-mm1.orig/fs/proc/base.c	2008-07-08 09:05:13.000000000 +0200
> +++ linux-2.6.26-rc8-mm1/fs/proc/base.c	2008-07-08 09:18:12.000000000 +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-rc8-mm1/kernel/Makefile
> ===================================================================
> --- linux-2.6.26-rc8-mm1.orig/kernel/Makefile	2008-07-08 09:04:35.000000000 +0200
> +++ linux-2.6.26-rc8-mm1/kernel/Makefile	2008-07-08 09:19:14.000000000 +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-rc8-mm1/kernel/next_syscall_data.c
> ===================================================================
> --- /dev/null	1970-01-01 00:00:00.000000000 +0000
> +++ linux-2.6.26-rc8-mm1/kernel/next_syscall_data.c	2008-07-08 09:35:27.000000000 +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;
> +}
> +
> +static int fill_next_syscall_data(struct task_struct *task, int ndata,
> +				char *buffer)
> +{
> +	char *token, *buff = buffer;
> +	char *end;
> +	struct next_syscall_data *nsd = task->nsd;
> +	int i;
> +
> +	if (!nsd) {
> +		nsd = kmalloc(sizeof(*nsd), GFP_KERNEL);
> +		if (!nsd)
> +			return -ENOMEM;
> +		task->nsd = nsd;
> +	}
> +
> +	nsd->ndata = ndata;
> +
> +	i = 0;
> +	while ((token = strsep(&buff, " ")) != NULL && i < ndata) {
> +		long data;
> +
> +		if (!*token)
> +			goto out_free;
> +		data = simple_strtol(token, &end, 0);
> +		if (end == token || (*end && !isspace(*end)))
> +			goto out_free;
> +		nsd->data[i] = data;
> +		i++;
> +	}
> +
> +	if (i != ndata