Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757379AbZA0RMv (ORCPT ); Tue, 27 Jan 2009 12:12:51 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1756550AbZA0RJi (ORCPT ); Tue, 27 Jan 2009 12:09:38 -0500 Received: from serrano.cc.columbia.edu ([128.59.29.6]:57697 "EHLO serrano.cc.columbia.edu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756162AbZA0RJ0 (ORCPT ); Tue, 27 Jan 2009 12:09:26 -0500 From: Oren Laadan To: Andrew Morton Cc: Linus Torvalds , containers@lists.linux-foundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-api@vger.kernel.org, Thomas Gleixner , Serge Hallyn , Dave Hansen , Ingo Molnar , "H. Peter Anvin" , Alexander Viro , Oren Laadan Subject: [RFC v13][PATCH 05/14] x86 support for checkpoint/restart Date: Tue, 27 Jan 2009 12:08:03 -0500 Message-Id: <1233076092-8660-6-git-send-email-orenl@cs.columbia.edu> X-Mailer: git-send-email 1.6.0.1 In-Reply-To: <1233076092-8660-1-git-send-email-orenl@cs.columbia.edu> References: <1233076092-8660-1-git-send-email-orenl@cs.columbia.edu> X-No-Spam-Score: Local Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 19767 Lines: 780 Add logic to save and restore architecture specific state, including thread-specific state, CPU registers and FPU state. In addition, architecture capabilities are saved in an architecure specific extension of the header (cr_hdr_head_arch); Currently this includes only FPU capabilities. Currently only x86-32 is supported. Compiling on x86-64 will trigger an explicit error. Changelog[v12]: - A couple of missed calls to cr_hbuf_put() - Replace obsolete cr_debug() with pr_debug() Changelog[v9]: - Add arch-specific header that details architecture capabilities; split FPU restore to send capabilities only once. - Test for zero TLS entries in cr_write_thread() - Fix asm/checkpoint_hdr.h so it can be included from user-space Changelog[v7]: - Fix save/restore state of FPU Changelog[v5]: - Remove preempt_disable() when restoring debug registers Changelog[v4]: - Fix header structure alignment Changelog[v2]: - Pad header structures to 64 bits to ensure compatibility - Follow Dave Hansen's refactoring of the original post Signed-off-by: Oren Laadan Acked-by: Serge Hallyn Signed-off-by: Dave Hansen --- arch/x86/include/asm/checkpoint_hdr.h | 100 ++++++++++++++ arch/x86/mm/Makefile | 2 + arch/x86/mm/checkpoint.c | 236 +++++++++++++++++++++++++++++++++ arch/x86/mm/restart.c | 234 ++++++++++++++++++++++++++++++++ checkpoint/checkpoint.c | 19 +++- checkpoint/checkpoint_arch.h | 9 ++ checkpoint/restart.c | 17 ++- include/linux/checkpoint_hdr.h | 2 + 8 files changed, 613 insertions(+), 6 deletions(-) create mode 100644 arch/x86/include/asm/checkpoint_hdr.h create mode 100644 arch/x86/mm/checkpoint.c create mode 100644 arch/x86/mm/restart.c create mode 100644 checkpoint/checkpoint_arch.h diff --git a/arch/x86/include/asm/checkpoint_hdr.h b/arch/x86/include/asm/checkpoint_hdr.h new file mode 100644 index 0000000..f966e70 --- /dev/null +++ b/arch/x86/include/asm/checkpoint_hdr.h @@ -0,0 +1,100 @@ +#ifndef __ASM_X86_CKPT_HDR_H +#define __ASM_X86_CKPT_HDR_H +/* + * Checkpoint/restart - architecture specific headers x86 + * + * Copyright (C) 2008 Oren Laadan + * + * This file is subject to the terms and conditions of the GNU General Public + * License. See the file COPYING in the main directory of the Linux + * distribution for more details. + */ + +#include + +/* + * To maintain compatibility between 32-bit and 64-bit architecture flavors, + * keep data 64-bit aligned: use padding for structure members, and use + * __attribute__ ((aligned (8))) for the entire structure. + * + * Quoting Arnd Bergmann: + * "This structure has an odd multiple of 32-bit members, which means + * that if you put it into a larger structure that also contains 64-bit + * members, the larger structure may get different alignment on x86-32 + * and x86-64, which you might want to avoid. I can't tell if this is + * an actual problem here. ... In this case, I'm pretty sure that + * sizeof(cr_hdr_task) on x86-32 is different from x86-64, since it + * will be 32-bit aligned on x86-32." + */ + +/* i387 structure seen from kernel/userspace */ +#ifdef __KERNEL__ +#include +#else +#include +#endif + +struct cr_hdr_head_arch { + /* FIXME: add HAVE_HWFP */ + + __u16 has_fxsr; + __u16 has_xsave; + __u16 xstate_size; + __u16 _pading; +} __attribute__((aligned(8))); + +struct cr_hdr_thread { + /* FIXME: restart blocks */ + + __s16 gdt_entry_tls_entries; + __s16 sizeof_tls_array; + __s16 ntls; /* number of TLS entries to follow */ +} __attribute__((aligned(8))); + +struct cr_hdr_cpu { + /* see struct pt_regs (x86-64) */ + __u64 r15; + __u64 r14; + __u64 r13; + __u64 r12; + __u64 bp; + __u64 bx; + __u64 r11; + __u64 r10; + __u64 r9; + __u64 r8; + __u64 ax; + __u64 cx; + __u64 dx; + __u64 si; + __u64 di; + __u64 orig_ax; + __u64 ip; + __u64 cs; + __u64 flags; + __u64 sp; + __u64 ss; + + /* segment registers */ + __u64 ds; + __u64 es; + __u64 fs; + __u64 gs; + + /* debug registers */ + __u64 debugreg0; + __u64 debugreg1; + __u64 debugreg2; + __u64 debugreg3; + __u64 debugreg4; + __u64 debugreg5; + __u64 debugreg6; + __u64 debugreg7; + + __u32 uses_debug; + __u32 used_math; + + /* thread_xstate contents follow (if used_math) */ +} __attribute__((aligned(8))); + +#endif /* __ASM_X86_CKPT_HDR__H */ diff --git a/arch/x86/mm/Makefile b/arch/x86/mm/Makefile index fea4565..6527ea2 100644 --- a/arch/x86/mm/Makefile +++ b/arch/x86/mm/Makefile @@ -18,3 +18,5 @@ obj-$(CONFIG_K8_NUMA) += k8topology_64.o obj-$(CONFIG_ACPI_NUMA) += srat_$(BITS).o obj-$(CONFIG_MEMTEST) += memtest.o + +obj-$(CONFIG_CHECKPOINT_RESTART) += checkpoint.o restart.o diff --git a/arch/x86/mm/checkpoint.c b/arch/x86/mm/checkpoint.c new file mode 100644 index 0000000..243a15c --- /dev/null +++ b/arch/x86/mm/checkpoint.c @@ -0,0 +1,236 @@ +/* + * Checkpoint/restart - architecture specific support for x86 + * + * Copyright (C) 2008 Oren Laadan + * + * This file is subject to the terms and conditions of the GNU General Public + * License. See the file COPYING in the main directory of the Linux + * distribution for more details. + */ + +#include +#include + +#include +#include + +/* dump the thread_struct of a given task */ +int cr_write_thread(struct cr_ctx *ctx, struct task_struct *t) +{ + struct cr_hdr h; + struct cr_hdr_thread *hh = cr_hbuf_get(ctx, sizeof(*hh)); + struct thread_struct *thread; + struct desc_struct *desc; + int ntls = 0; + int n, ret; + + h.type = CR_HDR_THREAD; + h.len = sizeof(*hh); + h.parent = task_pid_vnr(t); + + thread = &t->thread; + + /* calculate no. of TLS entries that follow */ + desc = thread->tls_array; + for (n = GDT_ENTRY_TLS_ENTRIES; n > 0; n--, desc++) { + if (desc->a || desc->b) + ntls++; + } + + hh->gdt_entry_tls_entries = GDT_ENTRY_TLS_ENTRIES; + hh->sizeof_tls_array = sizeof(thread->tls_array); + hh->ntls = ntls; + + ret = cr_write_obj(ctx, &h, hh); + cr_hbuf_put(ctx, sizeof(*hh)); + if (ret < 0) + return ret; + + pr_debug("ntls %d\n", ntls); + if (ntls == 0) + return 0; + + /* + * For simplicity dump the entire array, cherry-pick upon restart + * FIXME: the TLS descriptors in the GDT should be called out and + * not tied to the in-kernel representation. + */ + ret = cr_kwrite(ctx, thread->tls_array, sizeof(thread->tls_array)); + + /* IGNORE RESTART BLOCKS FOR NOW ... */ + + return ret; +} + +#ifdef CONFIG_X86_64 + +#error "CONFIG_X86_64 unsupported yet." + +#else /* !CONFIG_X86_64 */ + +static void cr_save_cpu_regs(struct cr_hdr_cpu *hh, struct task_struct *t) +{ + struct thread_struct *thread = &t->thread; + struct pt_regs *regs = task_pt_regs(t); + + hh->bp = regs->bp; + hh->bx = regs->bx; + hh->ax = regs->ax; + hh->cx = regs->cx; + hh->dx = regs->dx; + hh->si = regs->si; + hh->di = regs->di; + hh->orig_ax = regs->orig_ax; + hh->ip = regs->ip; + hh->cs = regs->cs; + hh->flags = regs->flags; + hh->sp = regs->sp; + hh->ss = regs->ss; + + hh->ds = regs->ds; + hh->es = regs->es; + + /* + * for checkpoint in process context (from within a container) + * the GS and FS registers should be saved from the hardware; + * otherwise they are already sabed on the thread structure + */ + if (t == current) { + savesegment(gs, hh->gs); + savesegment(fs, hh->fs); + } else { + hh->gs = thread->gs; + hh->fs = thread->fs; + } + + /* + * for checkpoint in process context (from within a container), + * the actual syscall is taking place at this very moment; so + * we (optimistically) subtitute the future return value (0) of + * this syscall into the orig_eax, so that upon restart it will + * succeed (or it will endlessly retry checkpoint...) + */ + if (t == current) { + BUG_ON(hh->orig_ax < 0); + hh->ax = 0; + } +} + +static void cr_save_cpu_debug(struct cr_hdr_cpu *hh, struct task_struct *t) +{ + struct thread_struct *thread = &t->thread; + + /* debug regs */ + + /* + * for checkpoint in process context (from within a container), + * get the actual registers; otherwise get the saved values. + */ + + if (t == current) { + get_debugreg(hh->debugreg0, 0); + get_debugreg(hh->debugreg1, 1); + get_debugreg(hh->debugreg2, 2); + get_debugreg(hh->debugreg3, 3); + get_debugreg(hh->debugreg6, 6); + get_debugreg(hh->debugreg7, 7); + } else { + hh->debugreg0 = thread->debugreg0; + hh->debugreg1 = thread->debugreg1; + hh->debugreg2 = thread->debugreg2; + hh->debugreg3 = thread->debugreg3; + hh->debugreg6 = thread->debugreg6; + hh->debugreg7 = thread->debugreg7; + } + + hh->debugreg4 = 0; + hh->debugreg5 = 0; + + hh->uses_debug = !!(task_thread_info(t)->flags & TIF_DEBUG); +} + +static void cr_save_cpu_fpu(struct cr_hdr_cpu *hh, struct task_struct *t) +{ + hh->used_math = tsk_used_math(t) ? 1 : 0; +} + +static int cr_write_cpu_fpu(struct cr_ctx *ctx, struct task_struct *t) +{ + void *xstate_buf = cr_hbuf_get(ctx, xstate_size); + int ret; + + /* i387 + MMU + SSE logic */ + preempt_disable(); /* needed it (t == current) */ + + /* + * normally, no need to unlazy_fpu(), since TS_USEDFPU flag + * have been cleared when task was context-switched out... + * except if we are in process context, in which case we do + */ + if (t == current && (task_thread_info(t)->status & TS_USEDFPU)) + unlazy_fpu(current); + + /* + * For simplicity dump the entire structure. + * FIXME: need to be deliberate about what registers we are + * dumping for traceability and compatibility. + */ + memcpy(xstate_buf, t->thread.xstate, xstate_size); + preempt_enable(); /* needed it (t == current) */ + + ret = cr_kwrite(ctx, xstate_buf, xstate_size); + cr_hbuf_put(ctx, xstate_size); + + return ret; +} + +#endif /* CONFIG_X86_64 */ + +/* dump the cpu state and registers of a given task */ +int cr_write_cpu(struct cr_ctx *ctx, struct task_struct *t) +{ + struct cr_hdr h; + struct cr_hdr_cpu *hh = cr_hbuf_get(ctx, sizeof(*hh)); + int ret; + + h.type = CR_HDR_CPU; + h.len = sizeof(*hh); + h.parent = task_pid_vnr(t); + + cr_save_cpu_regs(hh, t); + cr_save_cpu_debug(hh, t); + cr_save_cpu_fpu(hh, t); + + pr_debug("math %d debug %d\n", hh->used_math, hh->uses_debug); + + ret = cr_write_obj(ctx, &h, hh); + if (ret < 0) + goto out; + + if (hh->used_math) + ret = cr_write_cpu_fpu(ctx, t); + out: + cr_hbuf_put(ctx, sizeof(*hh)); + return ret; +} + +int cr_write_head_arch(struct cr_ctx *ctx) +{ + struct cr_hdr h; + struct cr_hdr_head_arch *hh = cr_hbuf_get(ctx, sizeof(*hh)); + int ret; + + h.type = CR_HDR_HEAD_ARCH; + h.len = sizeof(*hh); + h.parent = 0; + + /* FPU capabilities */ + hh->has_fxsr = cpu_has_fxsr; + hh->has_xsave = cpu_has_xsave; + hh->xstate_size = xstate_size; + + ret = cr_write_obj(ctx, &h, hh); + cr_hbuf_put(ctx, sizeof(*hh)); + + return ret; +} diff --git a/arch/x86/mm/restart.c b/arch/x86/mm/restart.c new file mode 100644 index 0000000..f5c3f16 --- /dev/null +++ b/arch/x86/mm/restart.c @@ -0,0 +1,234 @@ +/* + * Checkpoint/restart - architecture specific support for x86 + * + * Copyright (C) 2008 Oren Laadan + * + * This file is subject to the terms and conditions of the GNU General Public + * License. See the file COPYING in the main directory of the Linux + * distribution for more details. + */ + +#include +#include + +#include +#include + +/* read the thread_struct into the current task */ +int cr_read_thread(struct cr_ctx *ctx) +{ + struct cr_hdr_thread *hh = cr_hbuf_get(ctx, sizeof(*hh)); + struct task_struct *t = current; + struct thread_struct *thread = &t->thread; + int parent, ret; + + parent = cr_read_obj_type(ctx, hh, sizeof(*hh), CR_HDR_THREAD); + if (parent < 0) { + ret = parent; + goto out; + } + + ret = -EINVAL; + +#if 0 /* activate when containers are used */ + if (parent != task_pid_vnr(t)) + goto out; +#endif + pr_debug("ntls %d\n", hh->ntls); + + if (hh->gdt_entry_tls_entries != GDT_ENTRY_TLS_ENTRIES || + hh->sizeof_tls_array != sizeof(thread->tls_array) || + hh->ntls < 0 || hh->ntls > GDT_ENTRY_TLS_ENTRIES) + goto out; + + if (hh->ntls > 0) { + struct desc_struct *desc; + int size, cpu; + + /* + * restore TLS by hand: why convert to struct user_desc if + * sys_set_thread_entry() will convert it back ? + */ + + size = sizeof(*desc) * GDT_ENTRY_TLS_ENTRIES; + desc = kmalloc(size, GFP_KERNEL); + if (!desc) { + ret = -ENOMEM; + goto out; + } + + ret = cr_kread(ctx, desc, size); + if (ret == 0) { + /* + * FIX: add sanity checks (eg. that values makes + * sense, that we don't overwrite old values, etc + */ + cpu = get_cpu(); + memcpy(thread->tls_array, desc, size); + load_TLS(thread, cpu); + put_cpu(); + } + kfree(desc); + } + + ret = 0; + out: + cr_hbuf_put(ctx, sizeof(*hh)); + return ret; +} + +#ifdef CONFIG_X86_64 + +#error "CONFIG_X86_64 unsupported yet." + +#else /* !CONFIG_X86_64 */ + +static int cr_load_cpu_regs(struct cr_hdr_cpu *hh, struct task_struct *t) +{ + struct thread_struct *thread = &t->thread; + struct pt_regs *regs = task_pt_regs(t); + + regs->bx = hh->bx; + regs->cx = hh->cx; + regs->dx = hh->dx; + regs->si = hh->si; + regs->di = hh->di; + regs->bp = hh->bp; + regs->ax = hh->ax; + regs->ds = hh->ds; + regs->es = hh->es; + regs->orig_ax = hh->orig_ax; + regs->ip = hh->ip; + regs->cs = hh->cs; + regs->flags = hh->flags; + regs->sp = hh->sp; + regs->ss = hh->ss; + + thread->gs = hh->gs; + thread->fs = hh->fs; + loadsegment(gs, hh->gs); + loadsegment(fs, hh->fs); + + return 0; +} + +static int cr_load_cpu_debug(struct cr_hdr_cpu *hh, struct task_struct *t) +{ + /* debug regs */ + + if (hh->uses_debug) { + set_debugreg(hh->debugreg0, 0); + set_debugreg(hh->debugreg1, 1); + /* ignore 4, 5 */ + set_debugreg(hh->debugreg2, 2); + set_debugreg(hh->debugreg3, 3); + set_debugreg(hh->debugreg6, 6); + set_debugreg(hh->debugreg7, 7); + } + + return 0; +} + +static int cr_load_cpu_fpu(struct cr_hdr_cpu *hh, struct task_struct *t) +{ + preempt_disable(); + + __clear_fpu(t); /* in case we used FPU in user mode */ + + if (!hh->used_math) + clear_used_math(); + + preempt_enable(); + return 0; +} + +static int cr_read_cpu_fpu(struct cr_ctx *ctx, struct task_struct *t) +{ + void *xstate_buf = cr_hbuf_get(ctx, xstate_size); + int ret; + + ret = cr_kread(ctx, xstate_buf, xstate_size); + if (ret < 0) + goto out; + + /* i387 + MMU + SSE */ + preempt_disable(); + + /* init_fpu() also calls set_used_math() */ + ret = init_fpu(current); + if (ret < 0) + return ret; + + memcpy(t->thread.xstate, xstate_buf, xstate_size); + preempt_enable(); + out: + cr_hbuf_put(ctx, xstate_size); + return 0; +} + +#endif /* CONFIG_X86_64 */ + +/* read the cpu state and registers for the current task */ +int cr_read_cpu(struct cr_ctx *ctx) +{ + struct cr_hdr_cpu *hh = cr_hbuf_get(ctx, sizeof(*hh)); + struct task_struct *t = current; + int parent, ret; + + parent = cr_read_obj_type(ctx, hh, sizeof(*hh), CR_HDR_CPU); + if (parent < 0) { + ret = parent; + goto out; + } + + ret = -EINVAL; + +#if 0 /* activate when containers are used */ + if (parent != task_pid_vnr(t)) + goto out; +#endif + /* FIX: sanity check for sensitive registers (eg. eflags) */ + + pr_debug("math %d debug %d\n", hh->used_math, hh->uses_debug); + + ret = cr_load_cpu_regs(hh, t); + if (ret < 0) + goto out; + ret = cr_load_cpu_debug(hh, t); + if (ret < 0) + goto out; + ret = cr_load_cpu_fpu(hh, t); + if (ret < 0) + goto out; + + if (hh->used_math) + ret = cr_read_cpu_fpu(ctx, t); + out: + cr_hbuf_put(ctx, sizeof(*hh)); + return ret; +} + +int cr_read_head_arch(struct cr_ctx *ctx) +{ + struct cr_hdr_head_arch *hh = cr_hbuf_get(ctx, sizeof(*hh)); + int parent, ret = 0; + + parent = cr_read_obj_type(ctx, hh, sizeof(*hh), CR_HDR_HEAD_ARCH); + if (parent < 0) { + ret = parent; + goto out; + } else if (parent != 0) + goto out; + + /* FIX: verify compatibility of architecture features */ + + /* verify FPU capabilities */ + if (hh->has_fxsr != cpu_has_fxsr || + hh->has_xsave != cpu_has_xsave || + hh->xstate_size != xstate_size) + ret = -EINVAL; + out: + cr_hbuf_put(ctx, sizeof(*hh)); + + return ret; +} diff --git a/checkpoint/checkpoint.c b/checkpoint/checkpoint.c index 35bf99b..9c5430d 100644 --- a/checkpoint/checkpoint.c +++ b/checkpoint/checkpoint.c @@ -20,6 +20,8 @@ #include #include +#include "checkpoint_arch.h" + /* unique checkpoint identifier (FIXME: should be per-container ?) */ static atomic_t cr_ctx_count = ATOMIC_INIT(0); @@ -105,7 +107,10 @@ static int cr_write_head(struct cr_ctx *ctx) ret = cr_write_obj(ctx, &h, hh); cr_hbuf_put(ctx, sizeof(*hh)); - return ret; + if (ret < 0) + return ret; + + return cr_write_head_arch(ctx); } /* write the checkpoint trailer */ @@ -160,8 +165,16 @@ static int cr_write_task(struct cr_ctx *ctx, struct task_struct *t) int ret; ret = cr_write_task_struct(ctx, t); - pr_debug("ret %d\n", ret); - + pr_debug("task_struct: ret %d\n", ret); + if (ret < 0) + goto out; + ret = cr_write_thread(ctx, t); + pr_debug("thread: ret %d\n", ret); + if (ret < 0) + goto out; + ret = cr_write_cpu(ctx, t); + pr_debug("cpu: ret %d\n", ret); + out: return ret; } diff --git a/checkpoint/checkpoint_arch.h b/checkpoint/checkpoint_arch.h new file mode 100644 index 0000000..ada1369 --- /dev/null +++ b/checkpoint/checkpoint_arch.h @@ -0,0 +1,9 @@ +#include + +extern int cr_write_head_arch(struct cr_ctx *ctx); +extern int cr_write_thread(struct cr_ctx *ctx, struct task_struct *t); +extern int cr_write_cpu(struct cr_ctx *ctx, struct task_struct *t); + +extern int cr_read_head_arch(struct cr_ctx *ctx); +extern int cr_read_thread(struct cr_ctx *ctx); +extern int cr_read_cpu(struct cr_ctx *ctx); diff --git a/checkpoint/restart.c b/checkpoint/restart.c index 4741f4a..f40b619 100644 --- a/checkpoint/restart.c +++ b/checkpoint/restart.c @@ -15,6 +15,8 @@ #include #include +#include "checkpoint_arch.h" + /** * cr_read_obj - read a whole record (cr_hdr followed by payload) * @ctx: checkpoint context @@ -142,9 +144,9 @@ static int cr_read_head(struct cr_ctx *ctx) ctx->oflags = hh->flags; - /* FIX: verify compatibility of release, version and machine */ + /* FIX: verify compatibility of release, version */ - ret = 0; + ret = cr_read_head_arch(ctx); out: cr_hbuf_put(ctx, sizeof(*hh)); return ret; @@ -214,8 +216,17 @@ static int cr_read_task(struct cr_ctx *ctx) int ret; ret = cr_read_task_struct(ctx); - pr_debug("ret %d\n", ret); + pr_debug("task_struct: ret %d\n", ret); + if (ret < 0) + goto out; + ret = cr_read_thread(ctx); + pr_debug("thread: ret %d\n", ret); + if (ret < 0) + goto out; + ret = cr_read_cpu(ctx); + pr_debug("cpu: ret %d\n", ret); + out: return ret; } diff --git a/include/linux/checkpoint_hdr.h b/include/linux/checkpoint_hdr.h index fcc0125..3efd009 100644 --- a/include/linux/checkpoint_hdr.h +++ b/include/linux/checkpoint_hdr.h @@ -12,6 +12,7 @@ #include #include +#include /* * To maintain compatibility between 32-bit and 64-bit architecture flavors, @@ -39,6 +40,7 @@ struct cr_hdr { /* header types */ enum { CR_HDR_HEAD = 1, + CR_HDR_HEAD_ARCH, CR_HDR_BUFFER, CR_HDR_STRING, -- 1.5.4.3 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/