linux/arch/powerpc/kernel/vdso.c

/*
 *    Copyright (C) 2004 Benjamin Herrenschmidt, IBM Corp.
 *			 <benh@kernel.crashing.org>
 *
 *  This program is free software; you can redistribute it and/or
 *  modify it under the terms of the GNU General Public License
 *  as published by the Free Software Foundation; either version
 *  2 of the License, or (at your option) any later version.
 */

#include <linux/config.h>
#include <linux/module.h>
#include <linux/errno.h>
#include <linux/sched.h>
#include <linux/kernel.h>
#include <linux/mm.h>
#include <linux/smp.h>
#include <linux/smp_lock.h>
#include <linux/stddef.h>
#include <linux/unistd.h>
#include <linux/slab.h>
#include <linux/user.h>
#include <linux/elf.h>
#include <linux/security.h>
#include <linux/bootmem.h>

#include <asm/pgtable.h>
#include <asm/system.h>
#include <asm/processor.h>
#include <asm/mmu.h>
#include <asm/mmu_context.h>
#include <asm/lmb.h>
#include <asm/machdep.h>
#include <asm/cputable.h>
#include <asm/sections.h>
#include <asm/firmware.h>
#include <asm/vdso.h>
#include <asm/vdso_datapage.h>

#undef DEBUG

#ifdef DEBUG
#define DBG(fmt...) printk(fmt)
#else
#define DBG(fmt...)
#endif

/* Max supported size for symbol names */
#define MAX_SYMNAME	64

extern char vdso32_start, vdso32_end;
static void *vdso32_kbase = &vdso32_start;
unsigned int vdso32_pages;
unsigned long vdso32_sigtramp;
unsigned long vdso32_rt_sigtramp;

#ifdef CONFIG_PPC64
extern char vdso64_start, vdso64_end;
static void *vdso64_kbase = &vdso64_start;
unsigned int vdso64_pages;
unsigned long vdso64_rt_sigtramp;
#endif /* CONFIG_PPC64 */

/*
 * The vdso data page (aka. systemcfg for old ppc64 fans) is here.
 * Once the early boot kernel code no longer needs to muck around
 * with it, it will become dynamically allocated
 */
static union {
	struct vdso_data	data;
	u8			page[PAGE_SIZE];
} vdso_data_store __attribute__((__section__(".data.page_aligned")));
struct vdso_data *vdso_data = &vdso_data_store.data;

/* Format of the patch table */
struct vdso_patch_def
{
	unsigned long	ftr_mask, ftr_value;
	const char	*gen_name;
	const char	*fix_name;
};

/* Table of functions to patch based on the CPU type/revision
 *
 * Currently, we only change sync_dicache to do nothing on processors
 * with a coherent icache
 */
static struct vdso_patch_def vdso_patches[] = {
	{
		CPU_FTR_COHERENT_ICACHE, CPU_FTR_COHERENT_ICACHE,
		"__kernel_sync_dicache", "__kernel_sync_dicache_p5"
	},
	{
		CPU_FTR_USE_TB, 0,
		"__kernel_gettimeofday", NULL
	},
};

/*
 * Some infos carried around for each of them during parsing at
 * boot time.
 */
struct lib32_elfinfo
{
	Elf32_Ehdr	*hdr;		/* ptr to ELF */
	Elf32_Sym	*dynsym;	/* ptr to .dynsym section */
	unsigned long	dynsymsize;	/* size of .dynsym section */
	char		*dynstr;	/* ptr to .dynstr section */
	unsigned long	text;		/* offset of .text section in .so */
};

struct lib64_elfinfo
{
	Elf64_Ehdr	*hdr;
	Elf64_Sym	*dynsym;
	unsigned long	dynsymsize;
	char		*dynstr;
	unsigned long	text;
};


#ifdef __DEBUG
static void dump_one_vdso_page(struct page *pg, struct page *upg)
{
	printk("kpg: %p (c:%d,f:%08lx)", __va(page_to_pfn(pg) << PAGE_SHIFT),
	       page_count(pg),
	       pg->flags);
	if (upg/* && pg != upg*/) {
		printk(" upg: %p (c:%d,f:%08lx)", __va(page_to_pfn(upg)
						       << PAGE_SHIFT),
		       page_count(upg),
		       upg->flags);
	}
	printk("\n");
}

static void dump_vdso_pages(struct vm_area_struct * vma)
{
	int i;

	if (!vma || test_thread_flag(TIF_32BIT)) {
		printk("vDSO32 @ %016lx:\n", (unsigned long)vdso32_kbase);
		for (i=0; i<vdso32_pages; i++) {
			struct page *pg = virt_to_page(vdso32_kbase +
						       i*PAGE_SIZE);
			struct page *upg = (vma && vma->vm_mm) ?
				follow_page(vma, vma->vm_start + i*PAGE_SIZE, 0)
				: NULL;
			dump_one_vdso_page(pg, upg);
		}
	}
	if (!vma || !test_thread_flag(TIF_32BIT)) {
		printk("vDSO64 @ %016lx:\n", (unsigned long)vdso64_kbase);
		for (i=0; i<vdso64_pages; i++) {
			struct page *pg = virt_to_page(vdso64_kbase +
						       i*PAGE_SIZE);
			struct page *upg = (vma && vma->vm_mm) ?
				follow_page(vma, vma->vm_start + i*PAGE_SIZE, 0)
				: NULL;
			dump_one_vdso_page(pg, upg);
		}
	}
}
#endif /* DEBUG */

/*
 * Keep a dummy vma_close for now, it will prevent VMA merging.
 */
static void vdso_vma_close(struct vm_area_struct * vma)
{
}

/*
 * Our nopage() function, maps in the actual vDSO kernel pages, they will
 * be mapped read-only by do_no_page(), and eventually COW'ed, either
 * right away for an initial write access, or by do_wp_page().
 */
static struct page * vdso_vma_nopage(struct vm_area_struct * vma,
				     unsigned long address, int *type)
{
	unsigned long offset = address - vma->vm_start;
	struct page *pg;
#ifdef CONFIG_PPC64
	void *vbase = (vma->vm_mm->task_size > TASK_SIZE_USER32) ?
		vdso64_kbase : vdso32_kbase;
#else
	void *vbase = vdso32_kbase;
#endif

	DBG("vdso_vma_nopage(current: %s, address: %016lx, off: %lx)\n",
	    current->comm, address, offset);

	if (address < vma->vm_start || address > vma->vm_end)
		return NOPAGE_SIGBUS;

	/*
	 * Last page is systemcfg.
	 */
	if ((vma->vm_end - address) <= PAGE_SIZE)
		pg = virt_to_page(vdso_data);
	else
		pg = virt_to_page(vbase + offset);

	get_page(pg);
	DBG(" ->page count: %d\n", page_count(pg));

	return pg;
}

static struct vm_operations_struct vdso_vmops = {
	.close	= vdso_vma_close,
	.nopage	= vdso_vma_nopage,
};

/*
 * This is called from binfmt_elf, we create the special vma for the
 * vDSO and insert it into the mm struct tree
 */
int arch_setup_additional_pages(struct linux_binprm *bprm,
				int executable_stack)
{
	struct mm_struct *mm = current->mm;
	struct vm_area_struct *vma;
	unsigned long vdso_pages;
	unsigned long vdso_base;
	int rc;

#ifdef CONFIG_PPC64
	if (test_thread_flag(TIF_32BIT)) {
		vdso_pages = vdso32_pages;
		vdso_base = VDSO32_MBASE;
	} else {
		vdso_pages = vdso64_pages;
		vdso_base = VDSO64_MBASE;
	}
#else
	vdso_pages = vdso32_pages;
	vdso_base = VDSO32_MBASE;
#endif

	current->mm->context.vdso_base = 0;

	/* vDSO has a problem and was disabled, just don't "enable" it for the
	 * process
	 */
	if (vdso_pages == 0)
		return 0;
	/* Add a page to the vdso size for the data page */
	vdso_pages ++;

	/*
	 * pick a base address for the vDSO in process space. We try to put it
	 * at vdso_base which is the "natural" base for it, but we might fail
	 * and end up putting it elsewhere.
	 */
	down_write(&mm->mmap_sem);
	vdso_base = get_unmapped_area(NULL, vdso_base,
				      vdso_pages << PAGE_SHIFT, 0, 0);
	if (IS_ERR_VALUE(vdso_base)) {
		rc = vdso_base;
		goto fail_mmapsem;
	}


	/* Allocate a VMA structure and fill it up */
	vma = kmem_cache_zalloc(vm_area_cachep, SLAB_KERNEL);
	if (vma == NULL) {
		rc = -ENOMEM;
		goto fail_mmapsem;
	}
	vma->vm_mm = mm;
	vma->vm_start = vdso_base;
	vma->vm_end = vma->vm_start + (vdso_pages << PAGE_SHIFT);

	/*
	 * our vma flags don't have VM_WRITE so by default, the process isn't
	 * allowed to write those pages.
	 * gdb can break that with ptrace interface, and thus trigger COW on
	 * those pages but it's then your responsibility to never do that on
	 * the "data" page of the vDSO or you'll stop getting kernel updates
	 * and your nice userland gettimeofday will be totally dead.
	 * It's fine to use that for setting breakpoints in the vDSO code
	 * pages though
	 */
	vma->vm_flags = VM_READ|VM_EXEC|VM_MAYREAD|VM_MAYWRITE|VM_MAYEXEC;
	vma->vm_flags |= mm->def_flags;
	vma->vm_page_prot = protection_map[vma->vm_flags & 0x7];
	vma->vm_ops = &vdso_vmops;

	/* Insert new VMA */
	rc = insert_vm_struct(mm, vma);
	if (rc)
		goto fail_vma;

	/* Put vDSO base into mm struct and account for memory usage */
	current->mm->context.vdso_base = vdso_base;
	mm->total_vm += (vma->vm_end - vma->vm_start) >> PAGE_SHIFT;
	up_write(&mm->mmap_sem);
	return 0;

 fail_vma:
	kmem_cache_free(vm_area_cachep, vma);
 fail_mmapsem:
	up_write(&mm->mmap_sem);
	return rc;
}

const char *arch_vma_name(struct vm_area_struct *vma)
{
	if (vma->vm_mm && vma->vm_start == vma->vm_mm->context.vdso_base)
		return "[vdso]";
	return NULL;
}



static void * __init find_section32(Elf32_Ehdr *ehdr, const char *secname,
				  unsigned long *size)
{
	Elf32_Shdr *sechdrs;
	unsigned int i;
	char *secnames;

	/* Grab section headers and strings so we can tell who is who */
	sechdrs = (void *)ehdr + ehdr->e_shoff;
	secnames = (void *)ehdr + sechdrs[ehdr->e_shstrndx].sh_offset;

	/* Find the section they want */
	for (i = 1; i < ehdr->e_shnum; i++) {
		if (strcmp(secnames+sechdrs[i].sh_name, secname) == 0) {
			if (size)
				*size = sechdrs[i].sh_size;
			return (void *)ehdr + sechdrs[i].sh_offset;
		}
	}
	*size = 0;
	return NULL;
}

static Elf32_Sym * __init find_symbol32(struct lib32_elfinfo *lib,
					const char *symname)
{
	unsigned int i;
	char name[MAX_SYMNAME], *c;

	for (i = 0; i < (lib->dynsymsize / sizeof(Elf32_Sym)); i++) {
		if (lib->dynsym[i].st_name == 0)
			continue;
		strlcpy(name, lib->dynstr + lib->dynsym[i].st_name,
			MAX_SYMNAME);
		c = strchr(name, '@');
		if (c)
			*c = 0;
		if (strcmp(symname, name) == 0)
			return &lib->dynsym[i];
	}
	return NULL;
}

/* Note that we assume the section is .text and the symbol is relative to
 * the library base
 */
static unsigned long __init find_function32(struct lib32_elfinfo *lib,
					    const char *symname)
{
	Elf32_Sym *sym = find_symbol32(lib, symname);

	if (sym == NULL) {
		printk(KERN_WARNING "vDSO32: function %s not found !\n",
		       symname);
		return 0;
	}
	return sym->st_value - VDSO32_LBASE;
}

static int vdso_do_func_patch32(struct lib32_elfinfo *v32,
				struct lib64_elfinfo *v64,
				const char *orig, const char *fix)
{
	Elf32_Sym *sym32_gen, *sym32_fix;

	sym32_gen = find_symbol32(v32, orig);
	if (sym32_gen == NULL) {
		printk(KERN_ERR "vDSO32: Can't find symbol %s !\n", orig);
		return -1;
	}
	if (fix == NULL) {
		sym32_gen->st_name = 0;
		return 0;
	}
	sym32_fix = find_symbol32(v32, fix);
	if (sym32_fix == NULL) {
		printk(KERN_ERR "vDSO32: Can't find symbol %s !\n", fix);
		return -1;
	}
	sym32_gen->st_value = sym32_fix->st_value;
	sym32_gen->st_size = sym32_fix->st_size;
	sym32_gen->st_info = sym32_fix->st_info;
	sym32_gen->st_other = sym32_fix->st_other;
	sym32_gen->st_shndx = sym32_fix->st_shndx;

	return 0;
}


#ifdef CONFIG_PPC64

static void * __init find_section64(Elf64_Ehdr *ehdr, const char *secname,
				  unsigned long *size)
{
	Elf64_Shdr *sechdrs;
	unsigned int i;
	char *secnames;

	/* Grab section headers and strings so we can tell who is who */
	sechdrs = (void *)ehdr + ehdr->e_shoff;
	secnames = (void *)ehdr + sechdrs[ehdr->e_shstrndx].sh_offset;

	/* Find the section they want */
	for (i = 1; i < ehdr->e_shnum; i++) {
		if (strcmp(secnames+sechdrs[i].sh_name, secname) == 0) {
			if (size)
				*size = sechdrs[i].sh_size;
			return (void *)ehdr + sechdrs[i].sh_offset;
		}
	}
	if (size)
		*size = 0;
	return NULL;
}

static Elf64_Sym * __init find_symbol64(struct lib64_elfinfo *lib,
					const char *symname)
{
	unsigned int i;
	char name[MAX_SYMNAME], *c;

	for (i = 0; i < (lib->dynsymsize / sizeof(Elf64_Sym)); i++) {
		if (lib->dynsym[i].st_name == 0)
			continue;
		strlcpy(name, lib->dynstr + lib->dynsym[i].st_name,
			MAX_SYMNAME);
		c = strchr(name, '@');
		if (c)
			*c = 0;
		if (strcmp(symname, name) == 0)
			return &lib->dynsym[i];
	}
	return NULL;
}

/* Note that we assume the section is .text and the symbol is relative to
 * the library base
 */
static unsigned long __init find_function64(struct lib64_elfinfo *lib,
					    const char *symname)
{
	Elf64_Sym *sym = find_symbol64(lib, symname);

	if (sym == NULL) {
		printk(KERN_WARNING "vDSO64: function %s not found !\n",
		       symname);
		return 0;
	}
#ifdef VDS64_HAS_DESCRIPTORS
	return *((u64 *)(vdso64_kbase + sym->st_value - VDSO64_LBASE)) -
		VDSO64_LBASE;
#else
	return sym->st_value - VDSO64_LBASE;
#endif
}

static int vdso_do_func_patch64(struct lib32_elfinfo *v32,
				struct lib64_elfinfo *v64,
				const char *orig, const char *fix)
{
	Elf64_Sym *sym64_gen, *sym64_fix;

	sym64_gen = find_symbol64(v64, orig);
	if (sym64_gen == NULL) {
		printk(KERN_ERR "vDSO64: Can't find symbol %s !\n", orig);
		return -1;
	}
	if (fix == NULL) {
		sym64_gen->st_name = 0;
		return 0;
	}
	sym64_fix = find_symbol64(v64, fix);
	if (sym64_fix == NULL) {
		printk(KERN_ERR "vDSO64: Can't find symbol %s !\n", fix);
		return -1;
	}
	sym64_gen->st_value = sym64_fix->st_value;
	sym64_gen->st_size = sym64_fix->st_size;
	sym64_gen->st_info = sym64_fix->st_info;
	sym64_gen->st_other = sym64_fix->st_other;
	sym64_gen->st_shndx = sym64_fix->st_shndx;

	return 0;
}

#endif /* CONFIG_PPC64 */


static __init int vdso_do_find_sections(struct lib32_elfinfo *v32,
					struct lib64_elfinfo *v64)
{
	void *sect;

	/*
	 * Locate symbol tables & text section
	 */

	v32->dynsym = find_section32(v32->hdr, ".dynsym", &v32->dynsymsize);
	v32->dynstr = find_section32(v32->hdr, ".dynstr", NULL);
	if (v32->dynsym == NULL || v32->dynstr == NULL) {
		printk(KERN_ERR "vDSO32: required symbol section not found\n");
		return -1;
	}
	sect = find_section32(v32->hdr, ".text", NULL);
	if (sect == NULL) {
		printk(KERN_ERR "vDSO32: the .text section was not found\n");
		return -1;
	}
	v32->text = sect - vdso32_kbase;

#ifdef CONFIG_PPC64
	v64->dynsym = find_section64(v64->hdr, ".dynsym", &v64->dynsymsize);
	v64->dynstr = find_section64(v64->hdr, ".dynstr", NULL);
	if (v64->dynsym == NULL || v64->dynstr == NULL) {
		printk(KERN_ERR "vDSO64: required symbol section not found\n");
		return -1;
	}
	sect = find_section64(v64->hdr, ".text", NULL);
	if (sect == NULL) {
		printk(KERN_ERR "vDSO64: the .text section was not found\n");
		return -1;
	}
	v64->text = sect - vdso64_kbase;
#endif /* CONFIG_PPC64 */

	return 0;
}

static __init void vdso_setup_trampolines(struct lib32_elfinfo *v32,
					  struct lib64_elfinfo *v64)
{
	/*
	 * Find signal trampolines
	 */

#ifdef CONFIG_PPC64
	vdso64_rt_sigtramp = find_function64(v64, "__kernel_sigtramp_rt64");
#endif
	vdso32_sigtramp	   = find_function32(v32, "__kernel_sigtramp32");
	vdso32_rt_sigtramp = find_function32(v32, "__kernel_sigtramp_rt32");
}

static __init int vdso_fixup_datapage(struct lib32_elfinfo *v32,
				       struct lib64_elfinfo *v64)
{
	Elf32_Sym *sym32;
#ifdef CONFIG_PPC64
	Elf64_Sym *sym64;

       	sym64 = find_symbol64(v64, "__kernel_datapage_offset");
	if (sym64 == NULL) {
		printk(KERN_ERR "vDSO64: Can't find symbol "
		       "__kernel_datapage_offset !\n");
		return -1;
	}
	*((int *)(vdso64_kbase + sym64->st_value - VDSO64_LBASE)) =
		(vdso64_pages << PAGE_SHIFT) -
		(sym64->st_value - VDSO64_LBASE);
#endif /* CONFIG_PPC64 */

	sym32 = find_symbol32(v32, "__kernel_datapage_offset");
	if (sym32 == NULL) {
		printk(KERN_ERR "vDSO32: Can't find symbol "
		       "__kernel_datapage_offset !\n");
		return -1;
	}
	*((int *)(vdso32_kbase + (sym32->st_value - VDSO32_LBASE))) =
		(vdso32_pages << PAGE_SHIFT) -
		(sym32->st_value - VDSO32_LBASE);

	return 0;
}

static __init int vdso_fixup_alt_funcs(struct lib32_elfinfo *v32,
				       struct lib64_elfinfo *v64)
{
	int i;

	for (i = 0; i < ARRAY_SIZE(vdso_patches); i++) {
		struct vdso_patch_def *patch = &vdso_patches[i];
		int match = (cur_cpu_spec->cpu_features & patch->ftr_mask)
			== patch->ftr_value;
		if (!match)
			continue;

		DBG("replacing %s with %s...\n", patch->gen_name,
		    patch->fix_name ? "NONE" : patch->fix_name);

		/*
		 * Patch the 32 bits and 64 bits symbols. Note that we do not
		 * patch the "." symbol on 64 bits.
		 * It would be easy to do, but doesn't seem to be necessary,
		 * patching the OPD symbol is enough.
		 */
		vdso_do_func_patch32(v32, v64, patch->gen_name,
				     patch->fix_name);
#ifdef CONFIG_PPC64
		vdso_do_func_patch64(v32, v64, patch->gen_name,
				     patch->fix_name);
#endif /* CONFIG_PPC64 */
	}

	return 0;
}


static __init int vdso_setup(void)
{
	struct lib32_elfinfo	v32;
	struct lib64_elfinfo	v64;

	v32.hdr = vdso32_kbase;
#ifdef CONFIG_PPC64
	v64.hdr = vdso64_kbase;
#endif
	if (vdso_do_find_sections(&v32, &v64))
		return -1;

	if (vdso_fixup_datapage(&v32, &v64))
		return -1;

	if (vdso_fixup_alt_funcs(&v32, &v64))
		return -1;

	vdso_setup_trampolines(&v32, &v64);

	return 0;
}

/*
 * Called from setup_arch to initialize the bitmap of available
 * syscalls in the systemcfg page
 */
static void __init vdso_setup_syscall_map(void)
{
	unsigned int i;
	extern unsigned long *sys_call_table;
	extern unsigned long sys_ni_syscall;


	for (i = 0; i < __NR_syscalls; i++) {
#ifdef CONFIG_PPC64
		if (sys_call_table[i*2] != sys_ni_syscall)
			vdso_data->syscall_map_64[i >> 5] |=
				0x80000000UL >> (i & 0x1f);
		if (sys_call_table[i*2+1] != sys_ni_syscall)
			vdso_data->syscall_map_32[i >> 5] |=
				0x80000000UL >> (i & 0x1f);
#else /* CONFIG_PPC64 */
		if (sys_call_table[i] != sys_ni_syscall)
			vdso_data->syscall_map_32[i >> 5] |=
				0x80000000UL >> (i & 0x1f);
#endif /* CONFIG_PPC64 */
	}
}


void __init vdso_init(void)
{
	int i;

#ifdef CONFIG_PPC64
	/*
	 * Fill up the "systemcfg" stuff for backward compatiblity
	 */
	strcpy(vdso_data->eye_catcher, "SYSTEMCFG:PPC64");
	vdso_data->version.major = SYSTEMCFG_MAJOR;
	vdso_data->version.minor = SYSTEMCFG_MINOR;
	vdso_data->processor = mfspr(SPRN_PVR);
	/*
	 * Fake the old platform number for pSeries and iSeries and add
	 * in LPAR bit if necessary
	 */
	vdso_data->platform = machine_is(iseries) ? 0x200 : 0x100;
	if (firmware_has_feature(FW_FEATURE_LPAR))
		vdso_data->platform |= 1;
	vdso_data->physicalMemorySize = lmb_phys_mem_size();
	vdso_data->dcache_size = ppc64_caches.dsize;
	vdso_data->dcache_line_size = ppc64_caches.dline_size;
	vdso_data->icache_size = ppc64_caches.isize;
	vdso_data->icache_line_size = ppc64_caches.iline_size;

	/*
	 * Calculate the size of the 64 bits vDSO
	 */
	vdso64_pages = (&vdso64_end - &vdso64_start) >> PAGE_SHIFT;
	DBG("vdso64_kbase: %p, 0x%x pages\n", vdso64_kbase, vdso64_pages);
#endif /* CONFIG_PPC64 */


	/*
	 * Calculate the size of the 32 bits vDSO
	 */
	vdso32_pages = (&vdso32_end - &vdso32_start) >> PAGE_SHIFT;
	DBG("vdso32_kbase: %p, 0x%x pages\n", vdso32_kbase, vdso32_pages);


	/*
	 * Setup the syscall map in the vDOS
	 */
	vdso_setup_syscall_map();
	/*
	 * Initialize the vDSO images in memory, that is do necessary
	 * fixups of vDSO symbols, locate trampolines, etc...
	 */
	if (vdso_setup()) {
		printk(KERN_ERR "vDSO setup failure, not enabled !\n");
		vdso32_pages = 0;
#ifdef CONFIG_PPC64
		vdso64_pages = 0;
#endif
		return;
	}

	/* Make sure pages are in the correct state */
	for (i = 0; i < vdso32_pages; i++) {
		struct page *pg = virt_to_page(vdso32_kbase + i*PAGE_SIZE);
		ClearPageReserved(pg);
		get_page(pg);

	}
#ifdef CONFIG_PPC64
	for (i = 0; i < vdso64_pages; i++) {
		struct page *pg = virt_to_page(vdso64_kbase + i*PAGE_SIZE);
		ClearPageReserved(pg);
		get_page(pg);
	}
#endif /* CONFIG_PPC64 */

	get_page(virt_to_page(vdso_data));
}

int in_gate_area_no_task(unsigned long addr)
{
	return 0;
}

int in_gate_area(struct task_struct *task, unsigned long addr)
{
	return 0;
}

struct vm_area_struct *get_gate_vma(struct task_struct *tsk)
{
	return NULL;
}